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Stoecker C, Shao Y, Schmidt N, Martin DH, Kissinger PJ. Impact of Check It: A Novel Community-Based Chlamydia Screening and Expedited Treatment Program for Young Black Men. Sex Transm Dis 2022; 49:1-4. [PMID: 34407010 PMCID: PMC8665060 DOI: 10.1097/olq.0000000000001526] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
OBJECTIVES This study aimed to estimate the impact of the Check It program, a novel community-based chlamydia seek, test, and treat program for young Black men who have sex with women, on test positivity rates for chlamydia in young Black women. METHODS We used a synthetic control model to compare chlamydia test positivity rates in Orleans Parish (intervention site) with other similar parishes (control sites) in Louisiana. We estimated a model that used all other parishes as potential contributors to a synthetic control for Louisiana as well as a sample limited to the 40 parishes in Louisiana with the largest Black populations. RESULTS The Check It program was associated with a 1.69-percentage-point decline in chlamydia positivity in the first full year of operation and a 2.44-percentage-point decline in chlamydia positivity in the second full year of operation compared with control sites with the largest Black populations (P = 0.05). Results were similar when the treatment site was compared with all other sites in Louisiana. CONCLUSIONS The Check It program was associated with a significant decline in chlamydia testing positivity rates among women in Orleans Parish compared with control sites. Screening of young Black men who have sex with women can decrease rates in women living in the same community. Future recommendations for chlamydia screening of young men should be considered.
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Affiliation(s)
- Charles Stoecker
- Department of Health Policy and Management, Tulane University School of Public Health and Tropical Medicine
| | - Yixue Shao
- Department of Health Policy and Management, Tulane University School of Public Health and Tropical Medicine
| | - Norine Schmidt
- Department of Epidemiology, Tulane University School of Public Health and Tropical Medicine
| | - David H. Martin
- Department of Epidemiology, Tulane University School of Public Health and Tropical Medicine
- Louisiana State University School of Medicine – Department of Internal Medicine, Section of Infectious Diseases
| | - Patricia J. Kissinger
- Department of Epidemiology, Tulane University School of Public Health and Tropical Medicine
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2
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The impact of infection-derived immunity on disease dynamics. J Math Biol 2021; 83:61. [PMID: 34773173 PMCID: PMC8589100 DOI: 10.1007/s00285-021-01681-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2021] [Revised: 07/20/2021] [Accepted: 10/13/2021] [Indexed: 12/04/2022]
Abstract
When modeling infectious diseases, it is common to assume that infection-derived immunity is either (1) non-existent or (2) perfect and lifelong. However there are many diseases in which infection-derived immunity is known to be present but imperfect. There are various ways in which infection-derived immunity can fail, which can ultimately impact the probability that an individual be reinfected by the same pathogen, as well as the long-run population-level prevalence of the pathogen. Here we discuss seven different models of imperfect infection-derived immunity, including waning, leaky and all-or-nothing immunity. For each model we derive the probability that an infected individual becomes reinfected during their lifetime, given that the system is at endemic equilibrium. This can be thought of as the impact that each of these infection-derived immunity failures have on reinfection. This measure is useful because it provides us with a way to compare different modes of failure of infection-derived immunity.
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3
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Lewis J, White PJ, Price MJ. Per-partnership transmission probabilities for Chlamydia trachomatis infection: evidence synthesis of population-based survey data. Int J Epidemiol 2021; 50:510-517. [PMID: 33349846 PMCID: PMC8128448 DOI: 10.1093/ije/dyaa202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/25/2020] [Indexed: 11/14/2022] Open
Abstract
Background Chlamydia is the most commonly diagnosed sexually transmitted infection worldwide. Mathematical models used to plan and assess control measures rely on accurate estimates of chlamydia’s natural history, including the probability of transmission within a partnership. Several methods for estimating transmission probability have been proposed, but all have limitations. Methods We have developed a new model for estimating per-partnership chlamydia transmission probabilities from infected to uninfected individuals, using data from population-based surveys. We used data on sexual behaviour and prevalent chlamydia infection from the second UK National Study of Sexual Attitudes and Lifestyles (Natsal-2) and the US National Health and Nutrition Examination Surveys 2009–2014 (NHANES) for Bayesian inference of average transmission probabilities, across all new heterosexual partnerships reported. Posterior distributions were estimated by Markov chain Monte Carlo sampling using the Stan software. Results Posterior median male-to-female transmission probabilities per partnership were 32.1% [95% credible interval (CrI) 18.4–55.9%] (Natsal-2) and 34.9% (95%CrI 22.6–54.9%) (NHANES). Female-to-male transmission probabilities were 21.4% (95%CrI 5.1–67.0%) (Natsal-2) and 4.6% (95%CrI 1.0–13.1%) (NHANES). Posterior predictive checks indicated a well-specified model, although there was some discrepancy between reported and predicted numbers of partners, especially in women. Conclusions The model provides statistically rigorous estimates of per-partnership transmission probability, with associated uncertainty, which is crucial for modelling and understanding chlamydia epidemiology and control. Our estimates incorporate data from several sources, including population-based surveys, and use information contained in the correlation between number of partners and the probability of chlamydia infection. The evidence synthesis approach means that it is easy to include further data as it becomes available.
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Affiliation(s)
- Joanna Lewis
- MRC Centre for Global Infectious Disease Analysis and National Institute for Health Research (NIHR) Health Protection Research Unit in Modelling and Health Economics, Imperial College London School of Public Health, London, UK.,Centre for Applied Statistics Courses, UCL Great Ormond Street Institute of Child Health, University College London, London, UK
| | - Peter J White
- MRC Centre for Global Infectious Disease Analysis and National Institute for Health Research (NIHR) Health Protection Research Unit in Modelling and Health Economics, Imperial College London School of Public Health, London, UK.,Modelling and Economics Unit, National Infection Service, Public Health England, London, UK
| | - Malcolm J Price
- Institute of Applied Health Research, University of Birmingham, Birmingham, UK.,NIHR Birmingham Biomedical Research Centre, University Hospitals Birmingham NHS Foundation Trust and University of Birmingham, Birmingham, UK
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4
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Pillay J, Wingert A, MacGregor T, Gates M, Vandermeer B, Hartling L. Screening for chlamydia and/or gonorrhea in primary health care: systematic reviews on effectiveness and patient preferences. Syst Rev 2021; 10:118. [PMID: 33879251 PMCID: PMC8056106 DOI: 10.1186/s13643-021-01658-w] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 03/31/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND We conducted systematic reviews on the benefits and harms of screening compared with no screening or alternative screening approaches for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) in non-pregnant sexually active individuals, and on the relative importance patients' place on the relevant outcomes. Findings will inform recommendations by the Canadian Task Force on Preventive Health Care. METHODS We searched five databases (to January 24, 2020), trial registries, conference proceedings, and reference lists for English and French literature published since 1996. Screening, study selection, and risk of bias assessments were independently undertaken by two reviewers, with consensus for final decisions. Data extraction was conducted by one reviewer and checked by another for accuracy and completeness. Meta-analysis was conducted where appropriate. We used the GRADE approach to rate the certainty of the evidence. The Task Force and content experts provided input on determining thresholds for important effect sizes and on interpretation of findings. RESULTS Of 41 included studies, 17 and 11 reported on benefits and harms of screening, respectively, and 14 reported on patient preferences. Universal screening for CT in general populations 16 to 29 years of age, using population-based or opportunistic approaches achieving low screening rates, may make little-to-no difference for a female's risk of pelvic inflammatory disease (PID) (2 RCTs, n=141,362; 0.3 more in 1000 [7.6 fewer to 11 more]) or ectopic pregnancy (1 RCT, n=15,459; 0.20 more per 1000 [2.2 fewer to 3.9 more]). It may also not make a difference for CT transmission (3 RCTs, n=41,709; 3 fewer per 1000 [11.5 fewer to 6.9 more]). However, benefits may be achieved for reducing PID if screening rates are increased (2 trials, n=30,652; 5.7 fewer per 1000 [10.8 fewer to 1.1 more]), and for reducing CT and NG transmission when intensely screening high-prevalence female populations (2 trials, n=6127; 34.3 fewer per 1000 [4 to 58 fewer]; NNS 29 [17 to 250]). Evidence on infertility in females from CT screening and on transmission of NG in males and both sexes from screening for CT and NG is very uncertain. No evidence was found for cervicitis, chronic pelvic pain, or infertility in males from CT screening, or on any clinical outcomes from NG screening. Undergoing screening, or having a diagnosis of CT, may cause a small-to-moderate number of people to experience some degree of harm, mainly due to feelings of stigmatization and anxiety about future infertility risk. The number of individuals affected in the entire screening-eligible population is likely smaller. Screening may make little-to-no difference for general anxiety, self-esteem, or relationship break-up. Evidence on transmission from studies comparing home versus clinic screening is very uncertain. Four studies on patient preferences found that although utility values for the different consequences of CT and NG infections are probably quite similar, when considering the duration of the health state experiences, infertility and chronic pelvic pain are probably valued much more than PID, ectopic pregnancy, and cervicitis. How patients weigh the potential benefits versus harms of screening is very uncertain (1 survey, 10 qualitative studies); risks to reproductive health and transmission appear to be more important than the (often transient) psychosocial harms. DISCUSSION Most of the evidence on screening for CT and/or NG offers low or very low certainty about the benefits and harms. Indirectness from use of comparison groups receiving some screening, incomplete outcome ascertainment, and use of outreach settings was a major contributor to uncertainty. Patient preferences indicate that the potential benefits from screening appear to outweigh the possible harms. Direct evidence about which screening strategies and intervals to use, which age to start and stop screening, and whether screening males in addition to females is necessary to prevent clinical outcomes is scarce, and further research in these areas would be informative. Apart from the evidence in this review, information on factors related to equity, acceptability, implementation, cost/resources, and feasibility will support recommendations made by the Task Force. SYSTEMATIC REVIEW REGISTRATION International Prospective Register of Systematic Reviews (PROSPERO), registration number CRD42018100733 .
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Affiliation(s)
- Jennifer Pillay
- Alberta Research Centre for Health Evidence, Faculty of Medicine and Dentistry, University of Alberta, 11405 87 Avenue, Edmonton, Alberta, T6G 1C9, Canada.
| | - Aireen Wingert
- Alberta Research Centre for Health Evidence, Faculty of Medicine and Dentistry, University of Alberta, 11405 87 Avenue, Edmonton, Alberta, T6G 1C9, Canada
| | - Tara MacGregor
- Alberta Research Centre for Health Evidence, Faculty of Medicine and Dentistry, University of Alberta, 11405 87 Avenue, Edmonton, Alberta, T6G 1C9, Canada
| | - Michelle Gates
- Alberta Research Centre for Health Evidence, Faculty of Medicine and Dentistry, University of Alberta, 11405 87 Avenue, Edmonton, Alberta, T6G 1C9, Canada
| | - Ben Vandermeer
- Alberta Research Centre for Health Evidence, Faculty of Medicine and Dentistry, University of Alberta, 11405 87 Avenue, Edmonton, Alberta, T6G 1C9, Canada
| | - Lisa Hartling
- Alberta Research Centre for Health Evidence, Faculty of Medicine and Dentistry, University of Alberta, 11405 87 Avenue, Edmonton, Alberta, T6G 1C9, Canada
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5
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Qu Z, Azizi A, Schmidt N, Craig-Kuhn MC, Stoecker C, Hyman JM, Kissinger PJ. Effect of screening young men for Chlamydia trachomatis on the rates among women: a network modelling study for high-prevalence communities. BMJ Open 2021; 11:e040789. [PMID: 33483442 PMCID: PMC7831743 DOI: 10.1136/bmjopen-2020-040789] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
OBJECTIVE Chlamydia trachomatis (Ct) is the most commonly reported sexually transmitted infection in the USA and causes important reproductive morbidity in women. The Centers for Disease Control and Prevention recommend routine screening of sexually active women under age 25 but not among men. Despite three decades of screening women, chlamydia prevalence in women remains high. Untested and untreated men can serve as a reservoir of infection in women, and male-screening based intervention can be an effective strategy to reduce infection in women. We assessed the impact of screening men on the Ct prevalence in women. DESIGN We created an individual-based network model to simulate a realistic chlamydia epidemic on sexual contact networks for a synthetic population (n=5000). The model is calibrated to the ongoing routine screening among African American (AA) women in the USA and detailed a male-screening programme, Check It, that bundles best practices for Ct control. We used sensitivity analysis to quantify the relative importance of each intervention component. SETTING Community-based venues in New Orleans, Louisiana, USA. PARTICIPANTS Heterosexual AA men, aged 15 to 24, who had sex with women in the past 2 months. INTERVENTION Venue-based screening, expedited index treatment, expedited partner treatment and rescreening. RESULTS We estimate that by annually screening 7.5% of the AA male population in the age-range, the chlamydia prevalence would be reduced relatively by 8.1% (95% CI 5.9% to 10.4%) in AA women and 8.8% (95% CI 6.9% to 10.8%) in AA men. Each man screened could prevent 0.062 (95% CI 0.030 to 0.094) cases in men and 0.204 (95% CI 0.143 to 0.267) cases in women. The model suggested the importance of intervention components ranked from high to low as venue-based screening, expedited index treatment, expedited partner treatment and rescreening. CONCLUSION The findings indicated that male-screening has the potential to substantially reduce the prevalence among women in high-prevalence communities.
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Affiliation(s)
- Zhuolin Qu
- Department of Mathematics, Tulane University, New Orleans, Louisiana, USA
- Department of Mathematics, The University of Texas at San Antonio, San Antonio, Texas, USA
| | - Asma Azizi
- Simon A Levin Mathematical Computational Modeling Science Center, Arizona State University, Tempe, Arizona, USA
| | - Norine Schmidt
- Department of Epidemiology, Tulane University, New Orleans, Louisiana, USA
| | | | - Charles Stoecker
- Department of Health Policy and Management, Tulane University, New Orleans, Louisiana, USA
| | - James Mac Hyman
- Department of Mathematics, Tulane University, New Orleans, Louisiana, USA
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6
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Müller J, Kretzschmar M. Contact tracing - Old models and new challenges. Infect Dis Model 2020; 6:222-231. [PMID: 33506153 PMCID: PMC7806945 DOI: 10.1016/j.idm.2020.12.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Revised: 12/10/2020] [Accepted: 12/19/2020] [Indexed: 11/24/2022] Open
Abstract
Contact tracing is an effective method to control emerging infectious diseases. Since the 1980's, modellers are developing a consistent theory for contact tracing, with the aim to find effective and efficient implementations, and to assess the effects of contact tracing on the spread of an infectious disease. Despite the progress made in the area, there remain important open questions. In addition, technological developments, especially in the field of molecular biology (genetic sequencing of pathogens) and modern communication (digital contact tracing), have posed new challenges for the modelling community. In the present paper, we discuss modelling approaches for contact tracing and identify some of the current challenges for the field.
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Affiliation(s)
- Johannes Müller
- Mathematical Institute, Technical University of Munich, Boltzmannstr. 3, 85748, Garching, Germany
- Institute for Computational Biology, Helmholtz Center Munich, 85764, Neuherberg, Germany
| | - Mirjam Kretzschmar
- Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Heidelberglaan 100, 3584CX, Utrecht, the Netherlands
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7
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Geary RS, Copas AJ, Sonnenberg P, Tanton C, King E, Jones KG, Trifonova V, Johnson AM, Mercer CH. Sexual mixing in opposite-sex partnerships in Britain and its implications for STI risk: findings from the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3). Int J Epidemiol 2020; 48:228-242. [PMID: 30541028 PMCID: PMC6380304 DOI: 10.1093/ije/dyy237] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/09/2018] [Indexed: 01/29/2023] Open
Abstract
Background The extent to which individuals are similar to their sexual partners influences STI-transmission probabilities, yet there is a dearth of empirical data, especially those representative of the population. Methods Analyses of data reported by 10 759 sexually active people aged 16–74 y interviewed for a British national probability survey undertaken in 2010–12. Computer-assisted self-interviews asked about partner numbers and characteristics of participants’ three most recent partnerships (MRPs). Opposite-sex MRPs were weighted to represent all such partnerships in the past year (N = 16 451). Estimates of disassortative age mixing (≥±5-y difference), ethnic mixing (partner of a different ethnic group) and geographical mixing (partner from a different region/country when they first met) were calculated, stratified by gender, age group and partnership status (casual/steady). Multivariable regression examined how these disassortative mixing measures were associated with STI-risk measures: condom use at first sex together at the partnership-level and, at the participant-level, STI-risk perception and reporting STI diagnoses. Results Disassortative age mixing occurred in around one-third of opposite-sex partnerships, with men ≥5 y older in most cases, although this proportion varied by participant’s gender and age group. Ethnic mixing occurred less frequently (11.3% of men’s and 8.6% of women’s partnerships) as did geographical mixing (14.1 and 16.3%, respectively). Disassortative mixing was more common among casual vs steady partnerships. Condom use at first sex was less likely in women’s partnerships that were age-disassortative [adjusted odds ratio (AOR): 0.79, 95% confidence interval (CI): 0.69–0.95], whereas men reporting disassortative ethnic mixing were more likely to perceive themselves at STI risk (AOR: 1.76, 95% CI: 1.23–2.52) and report STI diagnoses (AOR: 2.37, 95% CI: 1.22–4.59). Conclusions Disassortative mixing, although uncommon among opposite-sex partnerships in Britain, is independently associated with STI risk, warranting consideration in STI-prevention efforts.
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Affiliation(s)
- Rebecca S Geary
- Institute for Global Health, University College London, London, UK
| | - Andrew J Copas
- Institute for Global Health, University College London, London, UK
| | - Pam Sonnenberg
- Institute for Global Health, University College London, London, UK
| | - Clare Tanton
- Institute for Global Health, University College London, London, UK
| | - Eleanor King
- Institute for Global Health, University College London, London, UK
| | - Kyle G Jones
- Institute for Global Health, University College London, London, UK
| | | | - Anne M Johnson
- Institute for Global Health, University College London, London, UK
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8
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Smid J, Althaus CL, Low N. Discrepancies between observed data and predictions from mathematical modelling of the impact of screening interventions on Chlamydia trachomatis prevalence. Sci Rep 2019; 9:7547. [PMID: 31101863 PMCID: PMC6525258 DOI: 10.1038/s41598-019-44003-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Accepted: 04/26/2019] [Indexed: 11/09/2022] Open
Abstract
Mathematical modelling studies of C. trachomatis transmission predict that interventions to screen and treat chlamydia infection will reduce prevalence to a greater degree than that observed in empirical population-based studies. We investigated two factors that might explain this discrepancy: partial immunity after natural infection clearance and differential screening coverage according to infection risk. We used four variants of a compartmental model for heterosexual C. trachomatis transmission, parameterized using data from England about sexual behaviour, C. trachomatis testing, diagnosis and prevalence, and Markov Chain Monte Carlo methods for statistical inference. In our baseline scenario, a model in which partial immunity follows natural infection clearance and the proportion of tests done in chlamydia-infected people decreases over time fitted the data best. The model predicts that partial immunity reduced susceptibility to reinfection by 68% (95% Bayesian credible interval 46-87%). The estimated screening rate was 4.3 (2.2-6.6) times higher for infected than for uninfected women in 2000, decreasing to 2.1 (1.4-2.9) in 2011. Despite incorporation of these factors, the model still predicted a marked decline in C. trachomatis prevalence. To reduce the gap between modelling and data, advances are needed in knowledge about factors influencing the coverage of chlamydia screening, the immunology of C. trachomatis and changes in C. trachomatis prevalence at the population level.
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Affiliation(s)
- Joost Smid
- Institute of Social and Preventive Medicine (ISPM), University of Bern, Bern, Switzerland
| | - Christian L Althaus
- Institute of Social and Preventive Medicine (ISPM), University of Bern, Bern, Switzerland.
| | - Nicola Low
- Institute of Social and Preventive Medicine (ISPM), University of Bern, Bern, Switzerland
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9
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Kasaie P, Schumacher CM, Jennings JM, Berry SA, Tuddenham SA, Shah MS, Rosenberg ES, Hoover KW, Gift TL, Chesson H, German D, Dowdy DW. Gonorrhoea and chlamydia diagnosis as an entry point for HIV pre-exposure prophylaxis: a modelling study. BMJ Open 2019; 9:e023453. [PMID: 30837248 PMCID: PMC6429744 DOI: 10.1136/bmjopen-2018-023453] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
OBJECTIVES Neisseria gonorrhoeae (NG) and Chlamydia trachomatis (CT) increase the risk of HIV transmission among men who have sex with men (MSM). Diagnosis of NG/CT may provide an efficient entry point for prevention of HIV through the delivery of pre-exposure prophylaxis (PrEP); however, the additional population-level impact of targeting PrEP to MSM diagnosed with NG/CT is unknown. DESIGN An agent-based simulation model of NG/CT and HIV cocirculation among MSM calibrated against census data, disease surveillance reports and the US National HIV Behavioral Surveillance study. SETTING Baltimore City, Maryland, USA. INTERVENTIONS PrEP implementation was modelled under three alternative scenarios: (1) PrEP delivery at NG/CT diagnosis (targeted delivery), (2) PrEP evaluation at NG/CT screening/testing and (3) PrEP evaluation in the general community (untargeted). MAIN OUTCOME The projected incidence of HIV after 20 years of PrEP delivery under two alternatives: when equal numbers of MSM are (1) screened for PrEP or (2) receive PrEP in each year. RESULTS Assuming 60% uptake and 60% adherence, targeting PrEP to MSM diagnosed with NG/CT could reduce HIV incidence among MSM in Baltimore City by 12.4% (95% uncertainty range (UR) 10.3% to 14.4%) in 20 years, relative to no PrEP. Expanding the coverage of NG/CT screening (such that individuals experience a 50% annual probability of NG/CT screening and evaluation for PrEP on NG/CT diagnosis) can further increase the impact of targeted PrEP to generate a 22.0% (95% UR 20.1% to 23.9%) reduction in HIV incidence within 20 years. When compared with alternative implementation scenarios, PrEP evaluation at NG/CT diagnosis increased impact of PrEP on HIV incidence by 1.5(95% UR 1.1 to 1.9) times relative to a scenario in which PrEP evaluation happened at the time of NG/CT screening/testing and by 1.6 (95% UR 1.2 to 2.2) times relative to evaluating random MSM from the community. CONCLUSIONS Targeting MSM infected with NG/CT increases the efficiency and effectiveness of PrEP delivery. If high levels of sexually transmitted infection screening can be achieved at the community level, NG/CT diagnosis may be a highly effective entry point for PrEP initialisation.
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Affiliation(s)
- Parastu Kasaie
- Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA
| | | | - Jacky M Jennings
- School of Medicine, Johns Hopkins University, Baltimore, Maryland, USA
| | - Stephen A Berry
- School of Medicine, Johns Hopkins University, Baltimore, Maryland, USA
| | - Susan A Tuddenham
- School of Medicine, Johns Hopkins University, Baltimore, Maryland, USA
| | - Maunank S Shah
- School of Medicine, Johns Hopkins University, Baltimore, Maryland, USA
| | - Eli S Rosenberg
- Rollins School of Public Health, Emory University, Atlanta, Georgia, USA
| | - Karen W Hoover
- Division of HIV/AIDS Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Thomas L Gift
- Division of STD Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, Atlanta, Georgia, USA
| | - Harrell Chesson
- Division of STD Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, Atlanta, Georgia, USA
| | - Danielle German
- Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA
| | - David W Dowdy
- Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA
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10
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Omori R, Chemaitelly H, Althaus CL, Abu-Raddad LJ. Does infection with Chlamydia trachomatis induce long-lasting partial immunity? Insights from mathematical modelling. Sex Transm Infect 2018; 95:115-121. [PMID: 30181327 PMCID: PMC6580764 DOI: 10.1136/sextrans-2018-053543] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Revised: 06/20/2018] [Accepted: 08/07/2018] [Indexed: 11/03/2022] Open
Abstract
OBJECTIVES To explore whether existence of long-lasting partial immunity against reinfection with Chlamydia trachomatis is necessary to explain C. trachomatis prevalence patterns by age and sexual risk, and to provide a plausible estimate for the effect size, defined here as a reduction in susceptibility to reinfection. METHODS A population-based mathematical model was constructed to describe C. trachomatis natural history and transmission dynamics by age and sexual risk. The model was parameterised using natural history, and epidemiological and sexual behaviour data, and applied for UK and US data. Sensitivity analyses were conducted to assess the robustness of predictions to variations in model structure and to examine the impact of alternative assumptions for the mechanism underlying partial immunity. RESULTS Partial immunity against reinfection was found necessary to explain observed C. trachomatis prevalence patterns by age and sexual risk. The reduction in susceptibility to reinfection was estimated at 93% using UK data (95% uncertainty interval (UI)=88%-97%) and at 67% using US data (95% UI=24%-88%). The model-structure sensitivity analyses affirmed model predictions. The immunity-mechanism sensitivity analyses suggested a mechanism of susceptibility reduction against reinfection or a mechanism of infectious-period duration reduction upon reinfection. CONCLUSIONS A strong long-lasting partial immunity against C. trachomatis reinfection should be present to explain observed prevalence patterns. The mechanism of immunity could be either a reduction in susceptibility to reinfection or a reduction in duration of infection on reinfection. C. trachomatis infection appears to naturally elicit a strong long-lasting immune response, supporting the concept of vaccine development.
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Affiliation(s)
- Ryosuke Omori
- Division of Bioinformatics, Research Center for Zoonosis Control, Hokkaido University, Sapporo, Japan .,JST, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama, Japan.,Infectious Disease Epidemiology Group, Weill Cornell Medicine-Qatar, Cornell University, Qatar Foundation - Education City, Doha, Qatar
| | - Hiam Chemaitelly
- Infectious Disease Epidemiology Group, Weill Cornell Medicine-Qatar, Cornell University, Qatar Foundation - Education City, Doha, Qatar
| | - Christian L Althaus
- Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland
| | - Laith J Abu-Raddad
- Infectious Disease Epidemiology Group, Weill Cornell Medicine-Qatar, Cornell University, Qatar Foundation - Education City, Doha, Qatar.,Department of Healthcare Policy and Research, Weill Cornell Medicine, Cornell University, New York City, New York, USA.,College of Health and Life Sciences, Hamad bin Khalifa University, Doha, Qatar
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11
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Yamamoto N, Ejima K, Nishiura H. Modelling the impact of correlations between condom use and sexual contact pattern on the dynamics of sexually transmitted infections. Theor Biol Med Model 2018; 15:6. [PMID: 29848374 PMCID: PMC5977462 DOI: 10.1186/s12976-018-0078-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Accepted: 05/09/2018] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND It is believed that sexually active people, i.e. people having multiple or concurrent sexual partners, are at a high risk of sexually transmitted infections (STI), but they are likely to be more aware of the risk and may exhibit greater fraction of the use of condom. The purpose of the present study is to examine the correlation between condom use and sexual contact pattern and clarify its impact on the transmission dynamics of STIs using a mathematical model. METHODS The definition of sexual contact pattern can be broad, but we focus on two specific aspects: (i) type of partnership (i.e. steady or casual partnership) and (ii) existence of concurrency (i.e. with single or multiple partners). Systematic review and meta-analysis of published studies are performed, analysing literature that epidemiologically examined the relationship between condom use and sexual contact pattern. Subsequently, we employ an epidemiological model and compute the reproduction number that accounts for with and without concurrency so that the corresponding coverage of condom use and its correlation with existence of concurrency can be explicitly investigated using the mathematical model. Combining the model with parameters estimated from the meta-analysis along with other assumed parameters, the impact of varying the proportion of population with multiple partners on the reproduction number is examined. RESULTS Based on systematic review, we show that a greater number of people used condoms during sexual contact with casual partners than with steady partners. Furthermore, people with multiple partners use condoms more frequently than people with a single partner alone. Our mathematical model revealed a positive relationship between the effective reproduction number and the proportion of people with multiple partners. Nevertheless, the association was reversed to be negative by employing a slightly greater value of the relative risk of condom use for people with multiple partners than that empirically estimated. CONCLUSIONS Depending on the correlation between condom use and the existence of concurrency, association between the proportion of people with multiple partners and the reproduction number can be reversed, suggesting the sexually active population is not necessary a primary target population to encourage condom use (i.e., sexually less active individuals could equivalently be a target in some cases).
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Affiliation(s)
- Nao Yamamoto
- Graduate School of Medicine, Hokkaido University, Hokkaido, Japan
- CREST, Japan Science and Technology Agency, Saitama, Japan
| | - Keisuke Ejima
- Institute of Industrial Science, The University of Tokyo, Tokyo, Japan
- Epidemiology and Biostatistics, School of Public Health, Indiana University Bloomington, Bloomington, IN USA
| | - Hiroshi Nishiura
- Graduate School of Medicine, Hokkaido University, Hokkaido, Japan
- CREST, Japan Science and Technology Agency, Saitama, Japan
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12
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Using Multiple Outcomes of Sexual Behavior to Provide Insights Into Chlamydia Transmission and the Effectiveness of Prevention Interventions in Adolescents. Sex Transm Dis 2018; 44:619-626. [PMID: 28876313 DOI: 10.1097/olq.0000000000000653] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Mathematical models are important tools for assessing prevention and management strategies for sexually transmitted infections. These models are usually developed for a single infection and require calibration to observed epidemiological trends in the infection of interest. Incorporating other outcomes of sexual behavior into the model, such as pregnancy, may better inform the calibration process. METHODS We developed a mathematical model of chlamydia transmission and pregnancy in Minnesota adolescents aged 15 to 19 years. We calibrated the model to statewide rates of reported chlamydia cases alone (chlamydia calibration) and in combination with pregnancy rates (dual calibration). We evaluated the impact of calibrating to different outcomes of sexual behavior on estimated input parameter values, predicted epidemiological outcomes, and predicted impact of chlamydia prevention interventions. RESULTS The two calibration scenarios produced different estimates of the probability of condom use, the probability of chlamydia transmission per sex act, the proportion of asymptomatic infections, and the screening rate among men. These differences resulted in the dual calibration scenario predicting lower prevalence and incidence of chlamydia compared with calibrating to chlamydia cases alone. When evaluating the impact of a 10% increase in condom use, the dual calibration scenario predicted fewer infections averted over 5 years compared with chlamydia calibration alone [111 (6.8%) vs 158 (8.5%)]. CONCLUSIONS While pregnancy and chlamydia in adolescents are often considered separately, both are outcomes of unprotected sexual activity. Incorporating both as calibration targets in a model of chlamydia transmission resulted in different parameter estimates, potentially impacting the intervention effectiveness predicted by the model.
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13
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Smid JH, Garcia V, Low N, Mercer CH, Althaus CL. Age difference between heterosexual partners in Britain: Implications for the spread of Chlamydia trachomatis. Epidemics 2018; 24:60-66. [PMID: 29655934 DOI: 10.1016/j.epidem.2018.03.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Revised: 03/23/2018] [Accepted: 03/30/2018] [Indexed: 11/28/2022] Open
Abstract
Heterosexual partners often differ in age. Integrating realistic patterns of sexual mixing by age into dynamic transmission models has been challenging. The effects of these patterns on the transmission of sexually transmitted infections (STI) including Chlamydia trachomatis (chlamydia), the most common bacterial STI are not well understood. We describe age mixing between new heterosexual partners using age- and sex-specific data about sexual behavior reported by people aged 16-63 years in the 2000 and 2010 British National Surveys of Sexual Attitudes and Lifestyles. We incorporate mixing patterns into a compartmental transmission model fitted to age- and sex-specific, chlamydia positivity from the same surveys, to investigate C. trachomatis transmission. We show that distributions of ages of new sex partners reported by women and by men in Britain are not consistent with each other. After balancing these distributions, new heterosexual partnerships tend to involve men who are older than women (median age difference 2, IQR -1, 5 years). We identified the most likely age combinations of heterosexual partners where incident C. trachomatis infections are generated. The model results show that in >50% of chlamydia transmitting partnerships, at least one partner is ≥25 years old. This study illustrates how sexual behavior data can be used to reconstruct detailed sexual mixing patterns by age, and how these patterns can be integrated into dynamic transmission models. The proposed framework can be extended to study the effects of age-dependent transmission on incidence in any STI.
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Affiliation(s)
- Joost H Smid
- University of Bern, Institute of Social and Preventive Medicine (ISPM), Switzerland.
| | - Victor Garcia
- University of Bern, Institute of Social and Preventive Medicine (ISPM), Switzerland
| | - Nicola Low
- University of Bern, Institute of Social and Preventive Medicine (ISPM), Switzerland
| | | | - Christian L Althaus
- University of Bern, Institute of Social and Preventive Medicine (ISPM), Switzerland
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14
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Pair formation models for sexually transmitted infections: A primer. Infect Dis Model 2017; 2:368-378. [PMID: 29928748 PMCID: PMC6002071 DOI: 10.1016/j.idm.2017.07.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2017] [Revised: 07/19/2017] [Accepted: 07/24/2017] [Indexed: 01/01/2023] Open
Abstract
For modelling sexually transmitted infections, duration of partnerships can strongly influence the transmission dynamics of the infection. If partnerships are monogamous, pairs of susceptible individuals are protected from becoming infected, while pairs of infected individuals delay onward transmission of the infection as long as they persist. In addition, for curable infections re-infection from an infected partner may occur. Furthermore, interventions based on contact tracing rely on the possibility of identifying and treating partners of infected individuals. To reflect these features in a mathematical model, pair formation models were introduced to mathematical epidemiology in the 1980's. They have since been developed into a widely used tool in modelling sexually transmitted infections and the impact of interventions. Here we give a basic introduction to the concepts of pair formation models for a susceptible-infected-susceptible (SIS) epidemic. We review some results and applications of pair formation models mainly in the context of chlamydia infection.
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15
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Azizi A, Ríos-Soto K, Mubayi A, M Hyman J. A Risk-based Model for Predicting the Impact of using Condoms on the Spread of Sexually Transmitted Infections. Infect Dis Model 2017; 2:100-112. [PMID: 28989988 PMCID: PMC5626461 DOI: 10.1016/j.idm.2017.02.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
We create and analyze a mathematical model to understand the impact of condom-use and sexual behavior on the prevalence and spread of Sexually Transmitted Infections (STIs). STIs remain significant public health challenges globally with a high burden of some Sexually Transmitted Diseases (STDs) in both developed and undeveloped countries. Although condom-use is known to reduce the transmission of STIs, there are a few quantitative population-based studies on the protective role of condom-use in reducing the incidence of STIs. The number of concurrent partners is correlated with their risk of being infectious by an STI such as chlamydia, gonorrhea, or syphilis. We develop a Susceptible-Infectious-Susceptible (SIS) model that stratifies the population based on the number of concurrent partners. The model captures the multi-level heterogeneous mixing through a combination of biased (preferential) and random (proportional) mixing processes between individuals with distinct risk levels, and accounts for differences in condom-use in the low- and high-risk populations. We use sensitivity analysis to assess the relative impact of high-risk people using condom as a prophylactic intervention to reduce their chance of being infectious, or infecting others. The model predicts the STI prevalence as a function of the number of partners of an individual, and quantifies how this distribution of effective partners changes as a function of condom-use. Our results show that when the mixing is random, then increasing the condom-use in the high-risk population is more effective in reducing the prevalence than when many of the partners of high-risk people have high risk. The model quantifies how the risk of being infected increases for people who have more partners, and the need for high-risk people to consistently use condoms to reduce their risk of infection.
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Affiliation(s)
- Asma Azizi
- Department of Mathematics, Tulane University, New Orleans, LA 70118
| | - Karen Ríos-Soto
- Department of Mathematical Sciences, University of Puerto Rico, Mayaguez P.R, 00610
| | - Anuj Mubayi
- School of Human Evolution and Social Change; Simon A. Levin Mathematical Computational Modeling Science Center, Arizona State University, Tempe, AZ
| | - James M Hyman
- Department of Mathematics, Tulane University, New Orleans, LA 70118
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16
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Price MJ, Ades AE, Soldan K, Welton NJ, Macleod J, Simms I, DeAngelis D, Turner KM, Horner PJ. The natural history of Chlamydia trachomatis infection in women: a multi-parameter evidence synthesis. Health Technol Assess 2016; 20:1-250. [PMID: 27007215 DOI: 10.3310/hta20220] [Citation(s) in RCA: 256] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND AND OBJECTIVES The evidence base supporting the National Chlamydia Screening Programme, initiated in 2003, has been questioned repeatedly, with little consensus on modelling assumptions, parameter values or evidence sources to be used in cost-effectiveness analyses. The purpose of this project was to assemble all available evidence on the prevalence and incidence of Chlamydia trachomatis (CT) in the UK and its sequelae, pelvic inflammatory disease (PID), ectopic pregnancy (EP) and tubal factor infertility (TFI) to review the evidence base in its entirety, assess its consistency and, if possible, arrive at a coherent set of estimates consistent with all the evidence. METHODS Evidence was identified using 'high-yield' strategies. Bayesian Multi-Parameter Evidence Synthesis models were constructed for separate subparts of the clinical and population epidemiology of CT. Where possible, different types of data sources were statistically combined to derive coherent estimates. Where evidence was inconsistent, evidence sources were re-interpreted and new estimates derived on a post-hoc basis. RESULTS An internally coherent set of estimates was generated, consistent with a multifaceted evidence base, fertility surveys and routine UK statistics on PID and EP. Among the key findings were that the risk of PID (symptomatic or asymptomatic) following an untreated CT infection is 17.1% [95% credible interval (CrI) 6% to 29%] and the risk of salpingitis is 7.3% (95% CrI 2.2% to 14.0%). In women aged 16-24 years, screened at annual intervals, at best, 61% (95% CrI 55% to 67%) of CT-related PID and 22% (95% CrI 7% to 43%) of all PID could be directly prevented. For women aged 16-44 years, the proportions of PID, EP and TFI that are attributable to CT are estimated to be 20% (95% CrI 6% to 38%), 4.9% (95% CrI 1.2% to 12%) and 29% (95% CrI 9% to 56%), respectively. The prevalence of TFI in the UK in women at the end of their reproductive lives is 1.1%: this is consistent with all PID carrying a relatively high risk of reproductive damage, whether diagnosed or not. Every 1000 CT infections in women aged 16-44 years, on average, gives rise to approximately 171 episodes of PID and 73 of salpingitis, 2.0 EPs and 5.1 women with TFI at age 44 years. CONCLUSIONS AND RESEARCH RECOMMENDATIONS The study establishes a set of interpretations of the major studies and study designs, under which a coherent set of estimates can be generated. CT is a significant cause of PID and TFI. CT screening is of benefit to the individual, but detection and treatment of incident infection may be more beneficial. Women with lower abdominal pain need better advice on when to seek early medical attention to avoid risk of reproductive damage. The study provides new insights into the reproductive risks of PID and the role of CT. Further research is required on the proportions of PID, EP and TFI attributable to CT to confirm predictions made in this report, and to improve the precision of key estimates. The cost-effectiveness of screening should be re-evaluated using the findings of this report. FUNDING The Medical Research Council grant G0801947.
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Affiliation(s)
- Malcolm J Price
- Institute of Applied Health Research, University of Birmingham, Birmingham, UK
| | - A E Ades
- School of Social and Community Medicine, University of Bristol, Bristol, UK
| | - Kate Soldan
- Public Health England (formerly Health Protection Agency), Colindale, London, UK
| | - Nicky J Welton
- School of Social and Community Medicine, University of Bristol, Bristol, UK
| | - John Macleod
- School of Social and Community Medicine, University of Bristol, Bristol, UK
| | - Ian Simms
- Public Health England (formerly Health Protection Agency), Colindale, London, UK
| | - Daniela DeAngelis
- Public Health England (formerly Health Protection Agency), Colindale, London, UK.,Medical Research Council Biostatistics Unit, Cambridge, UK
| | | | - Paddy J Horner
- School of Social and Community Medicine, University of Bristol, Bristol, UK.,Bristol Sexual Health Centre, University Hospital Bristol NHS Foundation Trust, Bristol, UK
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17
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Lanjouw E, Ouburg S, de Vries HJ, Stary A, Radcliffe K, Unemo M. Background review for the '2015 European guideline on the management of Chlamydia trachomatis infections'. Int J STD AIDS 2015:0956462415618838. [PMID: 26608578 DOI: 10.1177/0956462415618838] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
SummaryChlamydia trachomatis infections are major public health concerns globally. Of particular grave concern is that the majority of persons with anogenital Chlamydia trachomatis infections are asymptomatic and accordingly not aware of their infection, and this silent infection can subsequently result in severe reproductive tract complications and sequelae. The current review paper provides all background, evidence base and discussions for the 2015 European guideline on the management of Chlamydia trachomatis infections (Lanjouw E, et al. Int J STD AIDS 2015). Comprehensive information and recommendations are included regarding the diagnosis, treatment and prevention of anogenital, pharyngeal and conjunctival Chlamydia trachomatis infections in European countries. However, Chlamydia trachomatis also causes the eye infection trachoma, which is not a sexually transmitted infection. The 2015 European Chlamydia trachomatis guideline provides up-to-date guidance regarding broader indications for testing and treatment of Chlamydia trachomatis infections; clearer recommendation of using validated nucleic acid amplification tests only for diagnosis; advice on (repeated) Chlamydia trachomatis testing; recommendation of increased testing to reduce the incidence of pelvic inflammatory disease and prevent exposure to infection and recommendations to identify, verify and report Chlamydia trachomatis variants. Improvement of access to testing, test performance, diagnostics, antimicrobial treatment and follow-up of Chlamydia trachomatis patients are crucial to control its spread.
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Affiliation(s)
- E Lanjouw
- Department of Dermatology, Erasmus Medical Center, Rotterdam, The Netherlands
| | - S Ouburg
- Laboratory of Immunogenetics, Department of Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands
| | - H J de Vries
- Department of Dermatology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands STI Outpatient Clinic, Infectious Disease Cluster, Health Service Amsterdam, Amsterdam, The Netherlands Center for Infection and Immunology Amsterdam (CINIMA), Academic Medical Center (AMC), University of Amsterdam, Amsterdam, The Netherlands
| | - A Stary
- Outpatients' Centre for Infectious Venereodermatological Diseases, Vienna, Austria
| | - K Radcliffe
- University Hospital Birmingham Foundation NHS Trust, Birmingham, UK
| | - M Unemo
- WHO Collaborating Center for Gonorrhoea and other Sexually Transmitted Infections, National Reference Laboratory for Pathogenic Neisseria, Department of Laboratory Medicine, Microbiology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden
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18
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Teng Y, Kong N, Tu W. Estimating age-dependent per-encounter chlamydia trachomatis acquisition risk via a Markov-based state-transition model. J Clin Bioinforma 2014; 4:7. [PMID: 24872872 PMCID: PMC4022339 DOI: 10.1186/2043-9113-4-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2012] [Accepted: 04/07/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Chlamydial infection is a common bacterial sexually transmitted infection worldwide, caused by C. trachomatis. The screening for C. trachomatis has been proven to be successful. However, such success is not fully realized through tailoring the recommended screening strategies for different age groups. This is partly due to the knowledge gap in understanding how the infection is correlated with age. In this paper, we estimate age-dependent risks of acquiring C. trachomatis by adolescent women via unprotected heterosexual acts. METHODS We develop a time-varying Markov state-transition model and compute the incidences of chlamydial infection at discrete age points by simulating the state-transition model with candidate per-encounter acquisition risks and sampled numbers of unit-time unprotected coital events at different age points. We solve an optimization problem to identify the age-dependent estimates that offer the closest matches to the observed infection incidences. We also investigate the impact of antimicrobial treatment effectiveness on the parameter estimates and the differences between the acquisition risks for the first-time infections and repeated infections. RESULTS Our case study supports the beliefs that age is an inverse predictor of C. trachomatis transmission and that protective immunity developed after initial infection is only partial. CONCLUSIONS Our modeling method offers a flexible and expandable platform for investigating STI transmission.
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Affiliation(s)
- Yu Teng
- Weldon School of Biomedical Engineering, Purdue University, 206 S. Martin Jischke Dr, West Lafayette, IN 47907, USA
| | - Nan Kong
- Weldon School of Biomedical Engineering, Purdue University, 206 S. Martin Jischke Dr, West Lafayette, IN 47907, USA
| | - Wanzhu Tu
- Division of Biostatistics, School of Medicine, Indiana University, 340 W 10th Street, Indianapolis, IN 46202, USA
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19
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Davies B, Anderson SJ, Turner KME, Ward H. How robust are the natural history parameters used in chlamydia transmission dynamic models? A systematic review. Theor Biol Med Model 2014; 11:8. [PMID: 24476335 PMCID: PMC3922653 DOI: 10.1186/1742-4682-11-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Accepted: 01/18/2014] [Indexed: 11/10/2022] Open
Abstract
Transmission dynamic models linked to economic analyses often form part of the decision making process when introducing new chlamydia screening interventions. Outputs from these transmission dynamic models can vary depending on the values of the parameters used to describe the infection. Therefore these values can have an important influence on policy and resource allocation. The risk of progression from infection to pelvic inflammatory disease has been extensively studied but the parameters which govern the transmission dynamics are frequently neglected. We conducted a systematic review of transmission dynamic models linked to economic analyses of chlamydia screening interventions to critically assess the source and variability of the proportion of infections that are asymptomatic, the duration of infection and the transmission probability. We identified nine relevant studies in Pubmed, Embase and the Cochrane database. We found that there is a wide variation in their natural history parameters, including an absolute difference in the proportion of asymptomatic infections of 25% in women and 75% in men, a six-fold difference in the duration of asymptomatic infection and a four-fold difference in the per act transmission probability. We consider that much of this variation can be explained by a lack of consensus in the literature. We found that a significant proportion of parameter values were referenced back to the early chlamydia literature, before the introduction of nucleic acid modes of diagnosis and the widespread testing of asymptomatic individuals. In conclusion, authors should use high quality contemporary evidence to inform their parameter values, clearly document their assumptions and make appropriate use of sensitivity analysis. This will help to make models more transparent and increase their utility to policy makers.
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Affiliation(s)
- Bethan Davies
- School of Public Health, Imperial College London, St Mary's Campus, Praed Street, London W1 2PG, UK.
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20
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Best MD. Global approaches for the elucidation of phosphoinositide-binding proteins. Chem Phys Lipids 2013; 182:19-28. [PMID: 24220499 DOI: 10.1016/j.chemphyslip.2013.10.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Revised: 09/13/2013] [Accepted: 10/29/2013] [Indexed: 12/22/2022]
Abstract
Phosphoinositide lipids (PIPns) control numerous critical biological pathways, typically through the regulation of protein function driven by non-covalent protein-lipid binding interactions. Despite the importance of these systems, the unraveling of the full scope of protein-PIPn interactions has represented a significant challenge due to the massive complexity associated with these events, including the large number of diverse proteins that bind to these lipids, variations in the mechanisms by which proteins bind to lipids, and the presence of multiple distinct PIPn isomers. As a result of this complexity, global methods in which numerous proteins that bind PIPns can be identified and characterized simultaneously from complex samples, which have been enabled by key technological advancements, have become popular as an efficient means for tackling this challenge. This review article provides an overview of advancements in large-scale methods for profiling protein-PIPn binding, including experimental methods, such as affinity enrichment, microarray analysis and activity-based protein profiling, as well as computational methods, and combined computational/experimental efforts.
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Affiliation(s)
- Michael D Best
- Department of Chemistry, The University of Tennessee, 1420 Circle Drive, Knoxville, TN 37996, United States.
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21
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Abstract
OBJECTIVE To estimate the cost-effectiveness of anorectal chlamydia screening among men who have sex with men (MSM) in care at HIV treatment centers. DESIGN Transmission model combined with economic analysis over a 20-year period. SETTING AND PARTICIPANTS MSM in care at HIV treatment centers. INTERVENTION Once-yearly or twice-yearly screening for anorectal chlamydia among MSM in care at HIV treatment centers. MAIN OUTCOME MEASURES Averted HIV and chlamydia infections; discounted quality-adjusted life-years and costs; incremental cost-effectiveness ratio (ICER). RESULTS Costs will be saved by routine chlamydia screening of MSM in care at HIV treatment centers if these patients seek little or no screening elsewhere. Nonroutine screening is considerably more expensive than routine screening offered within a scheduled visit. Adding once-yearly chlamydia screening for MSM in care at HIV treatment centers is cost saving when 30% or fewer of those men seek once-yearly screening elsewhere (1.5 to 8.1 million euro saved). Twice-yearly routine screening at HIV treatment centers is cost-effective only when routine screening takes place without additional nonroutine screening (1.9 million euro saved). CONCLUSIONS Adding annual chlamydia screening to the HIV consultation will be cost saving as long as only a limited proportion of men are nonroutinely screened. The ICER was most sensitive to the percentage of MSM that continue to be screened elsewhere.
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Sanders LP, Söderberg B, Brockmann D, Ambjörnsson T. Perturbative solution to susceptible-infected-susceptible epidemics on networks. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:032713. [PMID: 24125300 DOI: 10.1103/physreve.88.032713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Revised: 07/20/2013] [Indexed: 06/02/2023]
Abstract
Herein we provide a closed form perturbative solution to a general M-node network susceptible-infected-susceptible (SIS) model using the transport rates between nodes as a perturbation parameter. We separate the dynamics into a short-time regime and a medium-to-long-time regime. We solve the short-time dynamics of the system and provide a limit before which our explicit, analytical result of the first-order perturbation for the medium-to-long-time regime is to be employed. These stitched calculations provide an approximation to the full temporal dynamics for rather general initial conditions. To further corroborate our results, we solve the mean-field equations numerically for an infectious SIS outbreak in New Zealand (NZ, Aotearoa) recomposed into 23 subpopulations where the virus is spread to different subpopulations via (documented) air traffic data, and the country is internationally quarantined. We demonstrate that our analytical predictions compare well to the numerical solution.
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Affiliation(s)
- Lloyd P Sanders
- Department of Astronomy and Theoretical Physics, Lund University, SE-223 62 Lund, Sweden
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23
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Hafner LM, Wilson DP, Timms P. Development status and future prospects for a vaccine against Chlamydia trachomatis infection. Vaccine 2013; 32:1563-71. [PMID: 23973245 DOI: 10.1016/j.vaccine.2013.08.020] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2013] [Revised: 07/04/2013] [Accepted: 08/11/2013] [Indexed: 01/08/2023]
Abstract
Chlamydia trachomatis continues to be the most commonly reported sexually transmitted bacterial infection in many countries with more than 100 million new cases estimated annually. These acute infections translate into significant downstream health care costs, particularly for women, where complications can include pelvic inflammatory disease and other disease sequelae such as tubal factor infertility. Despite years of research, the immunological mechanisms responsible for protective immunity versus immunopathology are still not well understood, although it is widely accepted that T cell driven IFN-g and Th17 responses are critical for clearing infection. While antibodies are able to neutralize infections in vitro, alone they are not protective, indicating that any successful vaccine will need to elicit both arms of the immune response. In recent years, there has been an expansion in the number and types of antigens that have been evaluated as vaccines, and combined with the new array of mucosal adjuvants, this aspect of chlamydial vaccinology is showing promise. Most recently, the opportunities to develop successful vaccines have been given a significant boost with the development of a genetic transformation system for Chlamydia, as well as the identification of the key role of the chlamydial plasmid in virulence. While still remaining a major challenge, the development of a successful C. trachomatis vaccine is starting to look more likely.
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Affiliation(s)
- Louise M Hafner
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia
| | - David P Wilson
- The Kirby Institute, University of New South Wales, Sydney, Australia
| | - Peter Timms
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia.
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Price MJ, Ades AE, Angelis DD, Welton NJ, Macleod J, Soldan K, Turner K, Simms I, Horner PJ. Mixture-of-exponentials models to explain heterogeneity in studies of the duration of Chlamydia trachomatis infection. Stat Med 2013; 32:1547-60. [PMID: 22949217 DOI: 10.1002/sim.5603] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Accepted: 08/12/2012] [Indexed: 11/09/2022]
Abstract
Published studies of the duration of asymptomatic Chlamydia trachomatis infection in women have produced diverse estimates, and most reviewers have not attempted an evidence synthesis. We review the designs of duration studies, distinguishing between the incident cases presenting soon after infection in clinic-based studies and prevalent cases ascertained in population screening studies. We combine evidence from all studies under fixed-effect (single clearance rate), random-effect (study-specific clearance rate), and mixture-of-exponentials models, in which there are either two or three classes of infection that clear at different rates. We can identify classes as 'passive' infection and fast-clearing and slow-clearing infections. We estimate models by Bayesian MCMC and compared them using posterior mean residual deviance and the deviance information criterion. The single fixed-effect clearance rate model fitted very poorly. The random-effect model was adequate but inferior to the two-class and three-class mixture of exponentials. According to the two-class model, the proportion in the first class was 23% (95% CI: 16-31%), and the mean duration of C. trachomatis infection is 1.36 years (95% CI: 1.13-1.63 years). With the three-rate model, duration was similar, but identification of the proportions in each class (19%, 31%, and 49%) was poor. Although the random-effect model was descriptively adequate, the extreme degree of between-study variation in the clearance rate it predicted lacked biological plausibility. Differences in study recruitment and sampling mechanisms, acting through a mixture-of-exponentials model, better explains the apparent heterogeneity in duration.
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Affiliation(s)
- Malcolm J Price
- School of Social and Community Medicine, University of Bristol, Bristol, UK
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Aicken CRH, Armstrong NT, Cassell JA, Macdonald N, Bailey AC, Johnson SA, Mercer CH. Barriers and opportunities for evidence-based health service planning: the example of developing a Decision Analytic Model to plan services for sexually transmitted infections in the UK. BMC Health Serv Res 2012; 12:202. [PMID: 22805183 PMCID: PMC3519719 DOI: 10.1186/1472-6963-12-202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Accepted: 06/28/2012] [Indexed: 11/10/2022] Open
Abstract
Background Decision Analytic Models (DAMs) are established means of evidence-synthesis to differentiate between health interventions. They have mainly been used to inform clinical decisions and health technology assessment at the national level, yet could also inform local health service planning. For this, a DAM must take into account the needs of the local population, but also the needs of those planning its services. Drawing on our experiences from stakeholder consultations, where we presented the potential utility of a DAM for planning local health services for sexually transmitted infections (STIs) in the UK, and the evidence it could use to inform decisions regarding different combinations of service provision, in terms of their costs, cost-effectiveness, and public health outcomes, we discuss the barriers perceived by stakeholders to the use of DAMs to inform service planning for local populations, including (1) a tension between individual and population perspectives; (2) reductionism; and (3) a lack of transparency regarding models, their assumptions, and the motivations of those generating models. Discussion Technological advances, including improvements in computing capability, are facilitating the development and use of models such as DAMs for health service planning. However, given the current scepticism among many stakeholders, encouraging informed critique and promoting trust in models to aid health service planning is vital, for example by making available and explicit the methods and assumptions underlying each model, associated limitations, and the process of validation. This can be achieved by consultation and training with the intended users, and by allowing access to the workings of the models, and their underlying assumptions (e.g. via the internet), to show how they actually work. Summary Constructive discussion and education will help build a consensus on the purposes of STI services, the need for service planning to be evidence-based, and the potential for mathematical tools like DAMs to facilitate this.
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Ong JBS, Fu X, Lee GKK, Chen MIC. Comparability of results from pair and classical model formulations for different sexually transmitted infections. PLoS One 2012; 7:e39575. [PMID: 22761828 PMCID: PMC3384672 DOI: 10.1371/journal.pone.0039575] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Accepted: 05/27/2012] [Indexed: 11/19/2022] Open
Abstract
The "classical model" for sexually transmitted infections treats partnerships as instantaneous events summarized by partner change rates, while individual-based and pair models explicitly account for time within partnerships and gaps between partnerships. We compared predictions from the classical and pair models over a range of partnership and gap combinations. While the former predicted similar or marginally higher prevalence at the shortest partnership lengths, the latter predicted self-sustaining transmission for gonorrhoea (GC) and Chlamydia (CT) over much broader partnership and gap combinations. Predictions on the critical level of condom use (C(c)) required to prevent transmission also differed substantially when using the same parameters. When calibrated to give the same disease prevalence as the pair model by adjusting the infectious duration for GC and CT, and by adjusting transmission probabilities for HIV, the classical model then predicted much higher C(c) values for GC and CT, while C(c) predictions for HIV were fairly close. In conclusion, the two approaches give different predictions over potentially important combinations of partnership and gap lengths. Assuming that it is more correct to explicitly model partnerships and gaps, then pair or individual-based models may be needed for GC and CT since model calibration does not resolve the differences.
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Affiliation(s)
- Jimmy Boon Som Ong
- Department of Clinical Epidemiology, Tan Tock Seng Hospital, Singapore, Singapore.
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Exploring short-term responses to changes in the control strategy for Chlamydia trachomatis. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2012; 2012:803097. [PMID: 22701143 PMCID: PMC3371724 DOI: 10.1155/2012/803097] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/02/2011] [Accepted: 04/06/2012] [Indexed: 11/18/2022]
Abstract
Chlamydia has a significant impact on public health provision in the developed world. Using pair approximation equations we investigate the efficacy of control programmes for chlamydia on short time scales that are relevant to policy makers. We use output from the model to estimate critical measures, namely, prevalence, incidence, and positivity in those screened and their partners. We combine these measures with a costing tool to estimate the economic impact of different public health strategies. Increasing screening coverage significantly increases the annual programme costs whereas an increase in tracing efficiency initially increases annual costs but over time reduces costs below baseline, with tracing accounting for around 10% of intervention costs. We found that partner positivity is insensitive to changes in prevalence due to screening, remaining at around 33%. Whether increases occur in screening or tracing levels, the cost per treated infection increases
from the baseline because of reduced prevalence.
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Schmid BV, Kretzschmar M. Determinants of sexual network structure and their impact on cumulative network measures. PLoS Comput Biol 2012; 8:e1002470. [PMID: 22570594 PMCID: PMC3343090 DOI: 10.1371/journal.pcbi.1002470] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Accepted: 02/24/2012] [Indexed: 11/19/2022] Open
Abstract
There are four major quantities that are measured in sexual behavior surveys that are thought to be especially relevant for the performance of sexual network models in terms of disease transmission. These are (i) the cumulative distribution of lifetime number of partners, (ii) the distribution of partnership durations, (iii) the distribution of gap lengths between partnerships, and (iv) the number of recent partners. Fitting a network model to these quantities as measured in sexual behavior surveys is expected to result in a good description of Chlamydia trachomatis transmission in terms of the heterogeneity of the distribution of infection in the population. Here we present a simulation model of a sexual contact network, in which we explored the role of behavioral heterogeneity of simulated individuals on the ability of the model to reproduce population-level sexual survey data from the Netherlands and UK. We find that a high level of heterogeneity in the ability of individuals to acquire and maintain (additional) partners strongly facilitates the ability of the model to accurately simulate the powerlaw-like distribution of the lifetime number of partners, and the age at which these partnerships were accumulated, as surveyed in actual sexual contact networks. Other sexual network features, such as the gap length between partnerships and the partnership duration, could-at the current level of detail of sexual survey data against which they were compared-be accurately modeled by a constant value (for transitional concurrency) and by exponential distributions (for partnership duration). Furthermore, we observe that epidemiological measures on disease prevalence in survey data can be used as a powerful tool for building accurate sexual contact networks, as these measures provide information on the level of mixing between individuals of different levels of sexual activity in the population, a parameter that is hard to acquire through surveying individuals.
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Affiliation(s)
- Boris V Schmid
- Unit Epidemiology & Surveillance, Centre for Infectious Disease Control, National Institute of Public Health and the Environment-RIVM, Bilthoven, The Netherlands.
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Risau-Gusman S. Influence of network dynamics on the spread of sexually transmitted diseases. J R Soc Interface 2011; 9:1363-72. [PMID: 22112655 DOI: 10.1098/rsif.2011.0445] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Network epidemiology often assumes that the relationships defining the social network of a population are static. The dynamics of relationships is only taken indirectly into account by assuming that the relevant information to study epidemic spread is encoded in the network obtained, by considering numbers of partners accumulated over periods of time roughly proportional to the infectious period of the disease. On the other hand, models explicitly including social dynamics are often too schematic to provide a reasonable representation of a real population, or so detailed that no general conclusions can be drawn from them. Here, we present a model of social dynamics that is general enough so its parameters can be obtained by fitting data from surveys about sexual behaviour, but that can still be studied analytically, using mean-field techniques. This allows us to obtain some general results about epidemic spreading. We show that using accumulated network data to estimate the static epidemic threshold lead to a significant underestimation of that threshold. We also show that, for a dynamic network, the relative epidemic threshold is an increasing function of the infectious period of the disease, implying that the static value is a lower bound to the real threshold. A practical example is given of how to apply the model to the study of a real population.
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Affiliation(s)
- Sebastián Risau-Gusman
- Consejo Nacional de Investigaciones Científicas y Técnicas, Centro Atómico Bariloche, 8400 San Carlos de Bariloche, Argentina.
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Sexual behaviour of Croatian blood donors as a threat to the health of blood recipients. BLOOD TRANSFUSION = TRASFUSIONE DEL SANGUE 2011; 9:407-12. [PMID: 21839015 DOI: 10.2450/2011.0084-10] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 09/21/2010] [Accepted: 03/23/2011] [Indexed: 11/21/2022]
Abstract
BACKGROUND In this cross-sectional study we assessed the prevalence of the various blood safety sexual risk behaviours among blood donors from East Croatia and the possibilities for improving the present blood donor screening procedure. MATERIALS AND METHODS The study included 423 blood donors of both sexes who completed a specially designed anonymous questionnaire immediately after their blood donations. The questionnaire contained questions on demographic data, sexual preferences, and possible sexual risk behaviours in the period before the blood donation. RESULTS The study revealed that the most common forms of sexual risk behaviour among Croatian blood donors had been irregular condom use during sexual contacts with new partners (294/423; 69.5%) and five or more sexual partners during the lifetime (213/423; 50.4%). More male than female subjects had had five or more sexual partners during their lifetime (p<0.0001). Compared to married donors, single subjects more frequently reported sexual contacts without using a condom with their new partners in the period from the last blood donation (p<0.0001) and also in the period of 1 month before current blood donation (p=0.0060). A larger number of younger than older subjects had practiced different types of sexual intercourses during the lifetime (p=0.0002) but more older than younger subjects reported irregular use of condom on sexual contacts with a new partner during their lifetime (p=0.0231). CONCLUSION Blood donors who were involved in various forms of sexual risk behaviour represent a serious threat to the health of blood recipients. In this respect a new approach to blood donor screening procedure with additional questions on sexual behaviour in anonymous donor questionnaires would improve the safety of transfusion treatment in East Croatia.
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Althaus CL, Turner KME, Schmid BV, Heijne JCM, Kretzschmar M, Low N. Transmission of Chlamydia trachomatis through sexual partnerships: a comparison between three individual-based models and empirical data. J R Soc Interface 2011; 9:136-46. [PMID: 21653569 DOI: 10.1098/rsif.2011.0131] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Chlamydia trachomatis is the most common bacterial sexually transmitted infection (STI) in many developed countries. The highest prevalence rates are found among young adults who have frequent partner change rates. Three published individual-based models have incorporated a detailed description of age-specific sexual behaviour in order to quantify the transmission of C. trachomatis in the population and to assess the impact of screening interventions. Owing to varying assumptions about sexual partnership formation and dissolution and the great uncertainty about critical parameters, such models show conflicting results about the impact of preventive interventions. Here, we perform a detailed evaluation of these models by comparing the partnership formation and dissolution dynamics with data from Natsal 2000, a population-based probability sample survey of sexual attitudes and lifestyles in Britain. The data also allow us to describe the dispersion of C. trachomatis infections as a function of sexual behaviour, using the Gini coefficient. We suggest that the Gini coefficient is a useful measure for calibrating infectious disease models that include risk structure and highlight the need to estimate this measure for other STIs.
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Affiliation(s)
- Christian L Althaus
- Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
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32
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Althaus CL, Heijne JC, Roellin A, Low N. Transmission dynamics of Chlamydia trachomatis affect the impact of screening programmes. Epidemics 2010; 2:123-131. [DOI: 10.1016/j.epidem.2010.04.002] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Revised: 04/13/2010] [Accepted: 04/19/2010] [Indexed: 11/29/2022] Open
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Hsieh YH, Wang YS, de Arazoza H, Lounes R. Modeling secondary level of HIV contact tracing: its impact on HIV intervention in Cuba. BMC Infect Dis 2010; 10:194. [PMID: 20594313 PMCID: PMC2909239 DOI: 10.1186/1471-2334-10-194] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Accepted: 07/01/2010] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND Universal HIV testing/treatment program has currently been suggested and debated as a useful strategy for elimination of HIV epidemic in Africa, although not without practical issues regarding the costs and feasibility of a fully implemented program. METHODS A mathematical model is proposed which considers two levels of detection of HIV-infectives through contact tracing of known infectives in addition to detections through other means such as random screening. Simulations based on Cuban contact tracing data were performed to ascertain the potential impact of the different levels of contact tracing. RESULTS Simulation studies illustrate that: (1) contact tracing is an important intervention measure which, while less effective than random screening, is perhaps less costly and hence ideal for large-scale intervention programs in developing countries with less resources; (2) the secondary level of contact tracing could significantly change the basic disease transmission dynamics, depending on the parameter values; (3) the prevalence of the epidemic at the time of implementation of contact tracing program might be a crucial factor in determining whether the measure will be effective in preventing disease infections and its eventual eradication. CONCLUSIONS Our results indicate that contact tracing for detection of HIV infectives could be suitably used to remedy inadequacies in a universal HIV testing program when designing timely and effective intervention measures.
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Affiliation(s)
- Ying-Hen Hsieh
- Department of Public Health and Institute of Biostatistics, China Medical University, Taichung, Taiwan 404
| | - Yun-Shih Wang
- Department of Applied Mathematics, National Chung Hsing University, Taichung, Taiwan 402
| | | | - Rachid Lounes
- Laboratoire MAP5, Université Paris Descartes, UMR-CNRS 8145, Paris, France
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Deogan CL, Hansson Bocangel MK, Wamala SP, Månsdotter AM. A cost-effectiveness analysis of the Chlamydia Monday - A community-based intervention to decrease the prevalence of chlamydia in Sweden. Scand J Public Health 2010; 38:141-50. [DOI: 10.1177/1403494809357260] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Aims: The study was undertaken to assess the cost-effectiveness of the Chlamydia Monday, 2007. This is a community-based intervention aimed at reducing the prevalence of chlamydia by information and increased availability of testing, treatment and contact tracing in Stockholm. The aim was to analyze the cost-effectiveness by estimating costs, savings and effects on health associated with the intervention, and to determine if cost-effectiveness varies between men and women. Methods: A societal perspective was adopted, meaning all significant costs and consequences were taken into consideration, regardless of who experienced them. A cost-effectiveness model was constructed including costs of the intervention, savings due to avoiding potential costs associated with medical sequels of chlamydia infection, and health gains measured as quality adjusted life years (QALY). Sensitivity analyses were done to explore model and result uncertainty. Results: Total costs were calculated to be 66,787.21; total savings to 30,370.14; and total health gains to 9.852324 QALYs (undiscounted figures). The discounted cost per QALY was 8,346.05 (10,810.77/QALY for women and 6,085.35/QALY for men). Sensitivity analyses included changes in effectiveness, variation of prevalence, reduced risk of sequel progression, inclusion of prevented future production loss and shortened duration for chronic conditions. The cost per QALY was consistently less than 50,000, which is often regarded as cost-effective in a Swedish context. Conclusions: The Chlamydia Monday has been demonstrated by this study to be a cost-effective intervention and should be considered a wise use of society’s resources.
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Affiliation(s)
| | | | - Sarah P. Wamala
- Swedish National Institute of Public Health & Karolinska Institute, Sweden
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Abstract
BACKGROUND With the world's largest population, HIV spread in China has been closely watched and widely studied by its government and the international community. One important factor that might contribute to the epidemic is China's numerous surplus of men, due to its imbalanced sex ratio in newborns. However, the sex ratio in the human population is often assumed to be 1:1 in most studies of sexually transmitted diseases (STDs). Here, a mathematical model is proposed to estimate the population size in each gender and within different stages of reproduction and sexual activities. This population profiling by age and gender will assist in more precise prediction of HIV incidences. METHOD The total population is divided into 6 subgroups by gender and age. A deterministic compartmental model is developed to describe birth, death, age and the interactions among different subgroups, with a focus on the preference for newborn boys and its impact for the sex ratios. Data from 2003 to 2007 is used to estimate model parameters, and simulations predict short-term and long-term population profiles. RESULTS The population of China will go to a descending track around 2030. Despite the possible underestimated number of newborns in the last couple of years, model-based simulations show that there will be about 28 million male individuals in 2055 without female partners during their sexually active stages. CONCLUSION The birth rate in China must be increased to keep the population viable. But increasing the birth rate without balancing the sex ratio in newborns is problematic, as this will generate a large number of surplus males. Besides other social, economic and psychological issues, the impact of this surplus of males on STD incidences, including HIV infections, must be dealt with as early as possible.
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Affiliation(s)
- Yuanyi Pan
- Centre for Disease Modeling, Department of Mathematics and Statistics, York University,Toronto, Ontario, Canada
| | - Jianhong Wu
- Centre for Disease Modeling, Department of Mathematics and Statistics, York University,Toronto, Ontario, Canada
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36
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The English National Chlamydia Screening Programme: Variations in Positivity in 2007/2008. Sex Transm Dis 2009; 36:522-7. [DOI: 10.1097/olq.0b013e3181a2aab9] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Risau-Gusman S, Zanette DH. Contact switching as a control strategy for epidemic outbreaks. J Theor Biol 2009; 257:52-60. [DOI: 10.1016/j.jtbi.2008.10.027] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2008] [Revised: 10/16/2008] [Accepted: 10/30/2008] [Indexed: 10/21/2022]
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Mercer CH, Copas AJ, Sonnenberg P, Johnson AM, McManus S, Erens B, Cassell JA. Who has sex with whom? Characteristics of heterosexual partnerships reported in a national probability survey and implications for STI risk. Int J Epidemiol 2008; 38:206-14. [PMID: 19001667 DOI: 10.1093/ije/dyn216] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Sexually transmitted infection (STI) risk is determined both by partner numbers and partnership characteristics. Studies describing only recent partnership(s) overestimate long-term partnerships and underestimate the contribution of casual partnerships to STI transmission in populations. We describe all heterosexual partnerships in the past year in terms of partnership type, age and geographical mixing and how these characteristics relate to condom use. METHODS Probability sample survey of 11 161 men and women aged 16-44 resident in Britain, 1999-2001. Computer-assisted self-interviews asked respondents about partner numbers and detailed questions about their three most recent partnerships. We weight these data to represent partnerships for which detailed questions were not asked to present estimates for the population of partnerships. RESULTS Of 15 488 heterosexuals partnerships, 39.1% (95% CI 36.6-41.7%) of men's partnerships were 'not (yet) regular' vs 20.0% (95% CI 18.2-21.9%) of women's partnerships. While condoms were used at last sex in 37.1% (95% CI 35.0-39.3%) of men's and 28.8% (95% CI 27.1-30.6%) of women's partnerships, and for 55.3% (95% CI 52.6-58.0%) of first sex with new partners, these proportions declined with age. When partnerships involved an age difference of 5+ years [26.2% (95% CI 23.0-29.6%) of men's and 36.5% (95% CI 33.0-40.1%) of women's partnerships], condoms were less commonly used at first sex than when partners were closer in age [44.1% (95% CI 39.1-48.4%) vs 60.8% (95% CI 57.3-64.2%)]. Sex occurred within 24 h in 23.4% (95% CI 19.7-27.5%) of men's and 10.7% (95% CI 8.3-13.6%) of women's partnerships. CONCLUSIONS A substantial minority of partnerships in the population is casual. The proportion of partnerships not protected by condoms is high, especially for partnerships involving larger age differences and people in their 30s and 40s. Condom use with new partners needs to be promoted among all age-groups.
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Affiliation(s)
- Catherine H Mercer
- Centre for Sexual Health & HIV Research, Research Department of Infection & Population Health, University College London, Mortimer Market Centre, London WC1E 6JB, UK.
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Chen MI, Ghani AC, Edmunds WJ. A metapopulation modelling framework for gonorrhoea and other sexually transmitted infections in heterosexual populations. J R Soc Interface 2008; 6:775-91. [PMID: 18986961 DOI: 10.1098/rsif.2008.0394] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Gonorrhoea continues to be a public health problem in the UK, and is the second most common bacterial sexually transmitted infection (STI) after chlamydia. In the UK, gonorrhoea is disproportionately concentrated in epidemiologically distinct subpopulations, with much higher incidence rates in young people, some ethnic minorities and inner city subpopulations. The original model of STI transmission proposed by Hethcote and Yorke explained some of these features through the concept of the 'core group'. Since then, several authors have modified the original model approach to include multiple sexual activity classes, but found this modelling approach to be inadequate when applied to low-prevalence settings such as the UK. We present a metapopulation framework for modelling gonorrhoea and other STIs. The model proposes that the epidemiology of gonorrhoea is largely driven by subpopulations with higher than average concentrations of individuals with high sexual risk activity. We show how this conceptualization of gonococcal epidemiology overcomes key limitations associated with some of the prior efforts to model gonorrhoea. We also use the model to explain several epidemiological features of gonorrhoea, such as its asymmetric distribution across subpopulations, and the contextual risk experienced by members of at-risk subpopulations. Finally, we extend the model to explain the distribution of other STIs, using chlamydia as an example of a more ubiquitous bacterial STI.
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Affiliation(s)
- Mark I Chen
- Health Protection Agency, Centre for Infections, London NW9 5EQ, UK.
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Adams EJ, Turner KME, Edmunds WJ. The cost effectiveness of opportunistic chlamydia screening in England. Sex Transm Infect 2007; 83:267-74; discussion 274-5. [PMID: 17475686 PMCID: PMC2598679 DOI: 10.1136/sti.2006.024364] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
BACKGROUND/AIM The National Chlamydia Screening Programme (NCSP) is being implemented in England. This study aims to estimate the cost effectiveness of (a) the NCSP strategy (annual screening offer to men and women aged under 25 years) and (b) alternative screening strategies. METHODS A stochastic, individual based, dynamic sexual network model was combined with a cost effectiveness model to estimate the complications and associated costs of chlamydial infection. The model was constructed and parameterised from the perspective of the National Health Service (NHS) (England), including the direct costs of infection, complications and screening. Unit costs were derived from standard data sources and published studies. The average and incremental cost effectiveness ratio (cost per major outcome averted or quality adjusted life year (QALY) gained) of chlamydia screening strategies targeting women and/or men of different age groups was estimated. Sensitivity analyses were done to explore model uncertainty. RESULTS All screening strategies modelled are likely to cost the NHS money and improve health. If pelvic inflammatory disease (PID) progression is less than 10% then screening at any level is unlikely to be cost effective. However, if PID progression is 10% or higher the NCSP strategy compared to no screening appears to be cost effective. The incremental cost effectiveness analysis suggests that screening men and women aged under 20 years is the most beneficial strategy that falls below accepted thresholds. There is a high degree of uncertainty in the findings. CONCLUSIONS Offering an annual screening test to men and women aged under 20 years may be the most cost effective strategy (that is, under accepted thresholds) if PID progression is 10% or higher.
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Affiliation(s)
- Elisabeth J Adams
- Modelling & Economics Unit, Health Protection Agency, 61 Colindale Avenue, Colindale, London NW9 5EQ, UK
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41
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Roberts TE, Robinson S, Barton PM, Bryan S, McCarthy A, Macleod J, Egger M, Low N. Cost effectiveness of home based population screening for Chlamydia trachomatis in the UK: economic evaluation of chlamydia screening studies (ClaSS) project. BMJ 2007; 335:291. [PMID: 17656504 PMCID: PMC1941857 DOI: 10.1136/bmj.39262.683345.ae] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 06/18/2007] [Indexed: 11/04/2022]
Abstract
OBJECTIVE To investigate the cost effectiveness of screening for Chlamydia trachomatis compared with a policy of no organised screening in the United Kingdom. DESIGN Economic evaluation using a transmission dynamic mathematical model. SETTING Central and southwest England. PARTICIPANTS Hypothetical population of 50,000 men and women, in which all those aged 16-24 years were invited to be screened each year. MAIN OUTCOME MEASURES Cost effectiveness based on major outcomes averted, defined as pelvic inflammatory disease, ectopic pregnancy, infertility, or neonatal complications. RESULTS The incremental cost per major outcome averted for a programme of screening women only (assuming eight years of screening) was 22,300 pounds (33,000 euros; $45,000) compared with no organised screening. For a programme screening both men and women, the incremental cost effectiveness ratio was approximately 28,900 pounds. Pelvic inflammatory disease leading to hospital admission was the most frequently averted major outcome. The model was highly sensitive to the incidence of major outcomes and to uptake of screening. When both were increased the cost effectiveness ratio fell to 6200 pound per major outcome averted for screening women only. CONCLUSIONS Proactive register based screening for chlamydia is not cost effective if the uptake of screening and incidence of complications are based on contemporary empirical studies, which show lower rates than commonly assumed. These data are relevant to discussions about the cost effectiveness of the opportunistic model of chlamydia screening being introduced in England.
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Affiliation(s)
- Tracy E Roberts
- Health Economics Facility, HSMC, University of Birmingham, Birmingham, Switzerland.
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Turner KME, Adams EJ, Lamontagne DS, Emmett L, Baster K, Edmunds WJ. Modelling the effectiveness of chlamydia screening in England. Sex Transm Infect 2006; 82:496-502. [PMID: 17151036 PMCID: PMC2563876 DOI: 10.1136/sti.2005.019067] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/03/2006] [Indexed: 11/04/2022] Open
Abstract
BACKGROUND Several developed countries have initiated chlamydia screening programmes. Screening for a sexually transmitted infection has both direct individual and indirect population-wide effects. Mathematical models can incorporate these non-linear effects and estimate the likely impact of different screening programmes and identify areas where more data are needed. METHODS A stochastic, individual based dynamic network model, parameterised from UK screening studies and data on sexual behaviour and chlamydia epidemiology, was used to investigate the likely impact of opportunistic screening on chlamydia prevalence. Three main strategies were considered for <25 year olds: (1) annual offer to women; (2) annual offer to women or if changed partner within last 6 months; (3) annual offer to men and women. Sensitivity analyses were performed for key screening parameters including uptake rate, targeted age range, percentage of partners notified, and screening interval. RESULTS Under strategy 1, continuous opportunistic screening of women <25 years of age is expected to reduce the population prevalence by over 50% after 5 years. Prevalence is also expected to decrease in unscreened older women and in men. For all three strategies screening those aged over 25 results in small additional reductions in prevalence. Including men led to a faster and greater reduction in overall prevalence, but involved approximately twice as many tests as strategy 1 and 10% more than strategy 2. The frequency of attendance at healthcare sites limits the number of opportunities to screen and the effect of changing the screening interval. CONCLUSIONS The model suggests that continuous opportunistic screening at high uptake rates could significantly reduced chlamydia prevalence within a few years. Opportunistic programmes depend on regular attendance at healthcare providers, but there is a lack of high quality data on patterns of attendance. Inequalities in coverage may result in a less efficient and less equitable outcome.
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Affiliation(s)
- K M E Turner
- Health Protection Agency, Centre for Infections, 61 Colindale Ave, Colindale, London NW9 5EQ, UK.
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