Comparative model-based analysis of screening programs for Chlamydia trachomatis infections

Sexually transmitted infections and dating app use

Incidence of sexually transmitted infections (STIs) is rising sharply in the United States. Between 2014 and 2019, incidence among men and women has increased by 62.8% and 21.4%, respectively, with an estimated 68 million Americans contracting an STI in 2018.a Some human behaviors impacting the expanding STI epidemic are unprotected sex and multiple sexual partners.b Increasing dating app usage has been postulated as a driver for increases in the numbers of people engaging in these behaviors. Using the proposed model, it is estimated that both STI incidence and prevalence for females and males have increased annually by 9%-15% between 2015 and 2019 due to dating apps usage, and that STI incidence and prevalence will continue to increase in the future. The model is also used to assess the possible benefit of in-app prevention campaigns.ahttps://www.cdc.gov/nchhstp/newsroom/fact-sheets/std/STI-Incidence-Prevalence-Cost-Factsheet.htmbA. N. Sawyer, E. R. Smith, and E. G. Benotsch. Dating application use and sexual risk behavior among young adults. Sexuality Research and Social Policy, 15:183-191, 2018.

Chlamydia trachomatis as a Current Health Problem: Challenges and Opportunities

Chlamydia is one of the most common sexually transmitted bacterial infections (STIs) worldwide. It is caused by Chlamydia trachomatis (CT), which is an obligate intracellular bacterium. In some cases, it can occur in coinfection with other parasites, increasing the pathologic potential of the infection. The treatment is based on antibiotic prescription; notwithstanding, the infection is mostly asymptomatic, which increases the risk of transmission. Therefore, some countries have implemented Chlamydia Screening Programs in order to detect undiagnosed infections. However, in Portugal, there is no CT screening plan within the National Health Service. There is no awareness in the general healthcare about the true magnitude of this issue because most of the methods used are not Nucleic Acid Amplification Technology-based and, therefore, lack sensitivity, resulting in underreporting infection cases. CT infections are also associated with possible long-term severe injuries. In detail, persistent infection triggers an inflammatory milieu and can be related to severe sequels, such as infertility. This infection could also trigger gynecologic tumors in women, evidencing the urgent need for cost-effective screening programs worldwide in order to detect and treat these individuals adequately. In this review, we have focused on the success of an implemented screening program that has been reported in the literature, the efforts made concerning the vaccine discovery, and what is known regarding CT infection. This review supports the need for further fundamental studies in this area in order to eradicate this infection and we also suggest the implementation of a Chlamydia Screening Program in Portugal.

Intensified partner notification and repeat testing can improve the effectiveness of screening in reducing Chlamydia trachomatis prevalence: a mathematical modelling study

BACKGROUND

The Australian Chlamydia Control Effectiveness Pilot (ACCEPt) was a cluster randomised controlled trial designed to assess the effectiveness of annual chlamydia testing through general practice in Australia. The trial showed that testing rates increased among sexually active men and women aged 16-29 years, but after 3 years the estimated chlamydia prevalence did not differ between intervention and control communities. We developed a mathematical model to estimate the potential longer-term impact of chlamydia testing on prevalence in the general population.

METHODS

We developed an individual-based model to simulate the transmission of Chlamydia trachomatis in a heterosexual population, calibrated to ACCEPt data. A proportion of the modelled population were tested for chlamydia and treated annually at coverage achieved in the control and intervention arms of ACCEPt. We estimated the reduction in chlamydia prevalence achieved by increasing retesting and by treating the partners of infected individuals up to 9 years after introduction of the intervention.

RESULTS

Increasing the testing coverage in the general Australian heterosexual population to the level achieved in the ACCEPt intervention arm resulted in reduction in the population-level prevalence of chlamydia from 4.6% to 2.7% in those aged 16-29 years old after 10 years (a relative reduction of 41%). The prevalence reduces to 2.2% if the proportion retested within 4 months of treatment is doubled from the rate achieved in the ACCEPt intervention arm (a relative reduction of 52%), and to 1.9% if the partner treatment rate is increased from 30%, as assumed in the base case, to 50% (a relative reduction of 59%).

CONCLUSION

A reduction in C. trachomatis prevalence could be achieved if the level of testing as observed in the ACCEPt intervention arm can be maintained at a population level. More substantial reductions can be achieved with intensified case management comprising retesting of those treated and treatment of partners of infected individuals.

Measuring Infection Transmission in a Stochastic SIV Model with Infection Reintroduction and Imperfect Vaccine

An additional compartment of vaccinated individuals is considered in a SIS stochastic epidemic model with infection reintroduction. The quantification of the spread of the disease is modeled by a continuous time Markov chain. A well-known measure of the initial transmission potential is the basic reproduction number [Formula: see text], which determines the herd immunity threshold or the critical proportion of immune individuals required to stop the spread of a disease when a vaccine offers a complete protection. Due to repeated contacts between the typical infective and previously infected individuals, [Formula: see text] overestimates the average number of secondary infections and leads to, perhaps unnecessary, high immunization coverage. Assuming that the vaccine is imperfect, alternative measures to [Formula: see text] are defined in order to study the influence of the initial coverage and vaccine efficacy on the transmission of the epidemic.

Using Multiple Outcomes of Sexual Behavior to Provide Insights Into Chlamydia Transmission and the Effectiveness of Prevention Interventions in Adolescents

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.

Genital Chlamydia trachomatis Infections Clear More Slowly in Men Than Women, but Are Less Likely to Become Established

Background

Rigorous estimates for clearance rates of untreated chlamydia infections are important for understanding chlamydia epidemiology and designing control interventions, but were previously only available for women.

Methods

We used data from published studies of chlamydia-infected men who were retested at a later date without having received treatment. Our analysis allowed new infections to take one of 1, 2, or 3 courses, each clearing at a different rate. We determined which of these 3 models had the most empirical support.

Results

The best-fitting model had 2 courses of infection in men, as was previously found for women: “slow-clearing” and “fast-clearing.” Only 68% (57%–78%) (posterior median and 95% credible interval [CrI]) of incident infections in men were slow-clearing, vs 77% (69%–84%) in women. The slow clearance rate in men (based on 6 months’ follow-up) was 0.35 (.05–1.15) year^-1 (posterior median and 95% CrI), corresponding to mean infection duration 2.84 (.87–18.79) years. This compares to 1.35 (1.13–1.63) years in women.

Conclusions

Our estimated clearance rate is slower than previously assumed. Fewer infections become established in men than women but once established, they clear more slowly. This study provides an improved description of chlamydia’s natural history to inform public health decision making. We describe how further data collection could reduce uncertainty in estimates.

Pair formation models for sexually transmitted infections: A primer

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.

A Risk-based Model for Predicting the Impact of using Condoms on the Spread of Sexually Transmitted Infections

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.

The natural history of Chlamydia trachomatis infection in women: a multi-parameter evidence synthesis

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.

Cost-effectiveness analysis of Chlamydia trachomatis screening in Dutch pregnant women

Chlamydia trachomatis infections during pregnancy may have serious consequences for women and their offspring. Chlamydial infections are largely asymptomatic. Hence, prevention is based on screening. The objective of this study was to estimate the cost-effectiveness of C. trachomatis screening during pregnancy. We used a health-economic decision analysis model, which included potential health outcomes of C. trachomatis infection for women, partners and infants, and premature delivery. We estimated the cost-effectiveness from a societal perspective using recent prevalence data from a population-based prospective cohort study among pregnant women in the Netherlands. We calculated the averted costs by linking health outcomes with health care costs and productivity losses. Cost-effectiveness was expressed as net costs per major outcome prevented and was estimated in base-case analysis, sensitivity, and scenario analysis. In the base-case analysis, the costs to detect 1000 pregnant women with C. trachomatis were estimated at €527,900. Prevention of adverse health outcomes averted €626,800 in medical costs, resulting in net cost savings. Sensitivity analysis showed that net cost savings remained with test costs up to €22 (test price €19) for a broad range of variation in underlying assumptions. Scenario analysis showed even more cost savings with targeted screening for women less than 30 years of age or with first pregnancies only. Antenatal screening for C. trachomatis is a cost-saving intervention when testing all pregnant women in the Netherlands. Savings increase even further when testing women younger than 30 years of age or with pregnancies only.

Why are men less tested for sexually transmitted infections in remote Australian Indigenous communities? A mixed-methods study

Gender disparities in testing rates for sexually transmitted infections (STIs) have been identified as one potential factor sustaining high rates of STIs and repeat infections in the Northern Territory of Australia, especially in remote Indigenous communities. The study aimed to investigate the reasons for these disparities utilising a mixed-method study design. We conducted an audit on client information at a remote community health clinic, focus-group discussions with young men in the same community and interviews with experienced remote area clinicians. The clinic audit found a significantly higher proportion of female residents of the community than males visited the clinic (72.8 versus 55.3%, p < 0.005). Women were also more likely to be tested for STIs than men when visiting the clinic (49.7 versus 40.3%, p = 0.015). Major barriers to men's seeking STI testing included a sense of shame from being seen visiting the clinic by women, men's lack of understanding of STIs and the need for testing, and inadequate access to male clinicians. Increasing men's access to healthcare and STI testing requires offering testing at a gender-sensitive and separate locations, and community-based sexual health promotion to increase knowledge of STIs.

Cost-Effectiveness of Opt-Out Chlamydia Testing for High-Risk Young Women in the U.S

INTRODUCTION

In spite of chlamydia screening recommendations, U.S. testing coverage continues to be low. This study explored the cost-effectiveness of a patient-directed, universal, opportunistic Opt-Out Testing strategy (based on insurance coverage, healthcare utilization, and test acceptance probabilities) for all women aged 15-24 years compared with current Risk-Based Screening (30% coverage) from a societal perspective.

METHODS

Based on insurance coverage (80%); healthcare utilization (83%); and test acceptance (75%), the proposed Opt-Out Testing strategy would have an expected annual testing coverage of approximately 50% for sexually active women aged 15-24 years. A basic compartmental heterosexual transmission model was developed to account for population-level transmission dynamics. Two groups were assumed based on self-reported sexual activity. All model parameters were obtained from the literature. Costs and benefits were tracked over a 50-year period. The relative sensitivity of the estimated incremental cost-effectiveness ratios to the variables/parameters was determined. This study was conducted in 2014-2015.

RESULTS

Based on the model, the Opt-Out Testing strategy decreased the overall chlamydia prevalence by >55% (2.7% to 1.2%). The Opt-Out Testing strategy was cost saving compared with the current Risk-Based Screening strategy. The estimated incremental cost-effectiveness ratio was most sensitive to the female pre-opt out prevalence, followed by the probability of female sequelae and discount rate.

CONCLUSIONS

The proposed Opt-Out Testing strategy was cost saving, improving health outcomes at a lower net cost than current testing. However, testing gaps would remain because many women might not have health insurance coverage, or not utilize health care.

Disease dynamics and costly punishment can foster socially imposed monogamy

Socially imposed monogamy in humans is an evolutionary puzzle because it requires costly punishment by those who impose the norm. Moreover, most societies were--and are--polygynous; yet many larger human societies transitioned from polygyny to socially imposed monogamy beginning with the advent of agriculture and larger residential groups. We use a simulation model to explore how interactions between group size, sexually transmitted infection (STI) dynamics and social norms can explain the timing and emergence of socially imposed monogamy. Polygyny dominates when groups are too small to sustain STIs. However, in larger groups, STIs become endemic (especially in concurrent polygynist networks) and have an impact on fertility, thereby mediating multilevel selection. Punishment of polygynists improves monogamist fitness within groups by reducing their STI exposure, and between groups by enabling punishing monogamist groups to outcompete polygynists. This suggests pathways for the emergence of socially imposed monogamy, and enriches our understanding of costly punishment evolution.

School-Based Sexually Transmitted Disease Screening: Review and Programmatic Guidance

School-based sexually transmitted disease (STD) screening (SBSS) was designed to provide chlamydia and gonorrhea testing, treatment, and counseling to adolescents in a school setting to overcome some of the difficulties of screening in this population. To inform STD control programs and other entities on decision making about potentially implementing this intervention, we reviewed existing published and gray literature on SBSS from 1998 to 2014. Although they are work-intensive to establish, school-based STD screening programs are a feasible and cost-effective way of testing large numbers of male and female adolescents for chlamydia and gonorrhea, and to provide counseling and treatment to almost all those who are found infected. School-based STD screening programs do not seem to reduce prevalence in either the school or the general adolescent population, although there are currently relatively few studies on large-scale SBSS. More research in this field is needed.

Optimizing strategies for population-based chlamydia infection screening among young women: an age-structured system dynamics approach

Background

Chlamydia infection (CT) is one of the most commonly reported sexually transmitted diseases. It is often referred to as a “silent” disease with the majority of infected people having no symptoms. Without early detection, it can progress to serious reproductive and other health problems. Economical identification of asymptomatically infected is a key public health challenge. Increasing evidence suggests that CT infection risk varies over the range of adolescence. Hence, age-dependent screening strategies with more frequent testing for certain age groups of higher risk may be cost-saving in controlling the disease.

Methods

We study the optimization of age-dependent screening strategies for population-based chlamydia infection screening among young women. We develop an age-structured compartment model for CT natural progress, screening, and treatment. We apply parameter optimization on the resultant PDE-based system dynamical models with the objective of minimizing the total care spending, including screening and treatment costs during the program period and anticipated costs of treating the sequelae afterwards). For ease of practical implementation, we also search for the best screening initiation age for strategies with a constant screening frequency.

Results

The optimal age-dependent strategies identified outperform the current CDC recommendations both in terms of total care spending and disease prevalence at the termination of the program. For example, the age-dependent strategy that allows monthly screening rate changes can save about 5 % of the total spending. Our results suggest early initiation of CT screening is likely beneficial to the cost saving and prevalence reduction. Finally, our results imply that the strategy design may not be sensitive to accurate quantification of the age-specific CT infection risk if screening initiation age and screening rate are the only decisions to make.

Conclusions

Our research demonstrates the potential economic benefit of age-dependent screening strategy design for population-based screening programs. It also showcases the applicability of age-structured system dynamical modeling to infectious disease control with increasing evidence on the age differences in infection risk. The research can be further improved with consideration of the difference between first-time infection and reinfection, as well as population heterogeneity in sexual partnership.

Chlamydia screening is not cost-effective at low participation rates: evidence from a repeated register-based implementation study in The Netherlands

OBJECTIVE

In three pilot regions of The Netherlands, all 16-29 year olds were invited to participate in three annual rounds of Chlamydia screening. The aim of the present study is to evaluate the cost-effectiveness of repeated Chlamydia screening, based on empirical data.

METHODS

A mathematical model was employed to estimate the influence of repeated screening on prevalence and incidence of Chlamydial infection. A model simulating the natural history of Chlamydia was combined with cost and utility data to estimate the number of major outcomes and quality-adjusted life-years (QALYs) associated with Chlamydia. Six screening scenarios (16-29 years annually; 16-24 years annually; women only; biennial screening; biennial screening women only; screening every five years) were compared with no screening in two sexual networks, representing both lower ('national network') and higher ('urban network') baseline prevalence. Incremental cost-effectiveness ratios (ICERs) for the different screening scenarios were estimated. Uncertainty and sensitivity analyses were performed.

RESULTS

In all scenarios and networks, cost per major outcome averted are above €5000. Cost per QALY are at least €50,000. The default scenario as piloted in the Netherlands was least cost-effective, with ICERs of €232,000 in the national and €145,000 in the urban sexual network. Results were robust in sensitivity analyses.

CONCLUSIONS

It is unlikely that repeated rounds of Chlamydia screening will be cost-effective. Only at high levels of willingness to pay for a QALY (>€50,000) screening may be more cost-effective than no screening.

ANALYSIS OF A CHLAMYDIA EPIDEMIC MODEL

In this paper, we have developed a five-compartmental epidemic model with Chlamydia infection. We have divided the total population into five classes, namely susceptible, exposed, infective in asymptomatic phase, infective in symptomatic phase and recovered class. The basic reproduction number (R0) is calculated using the next-generation matrix method. The stability analysis of the model shows that the system is locally asymptotically stable at the disease-free equilibrium (DFE) E0when R0< 1. When R0> 1, an endemic equilibrium E1exists and the system becomes locally asymptotically stable at E1under some conditions. We have also discussed the Chlamydia epidemic model with two treatment controls. An objective functional is considered which is based on a combination of minimizing the number of exposed and infective individuals and the cost of treatment. Then an optimal control pair is obtained which minimizes the objective functional. Our numerical findings are illustrated through computer simulations using MATLAB, which show the reliability of our model from the practical point of view. Epidemiological implications of our analytical findings are addressed critically.

Estimating age-dependent per-encounter chlamydia trachomatis acquisition risk via a Markov-based state-transition model

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.

How robust are the natural history parameters used in chlamydia transmission dynamic models? A systematic review

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.

Chlamydia screening coverage estimates derived using healthcare effectiveness data and information system procedures and indirect estimation vary substantially

BACKGROUND

Screening coverage is an important determinant of chlamydial control program success.

OBJECTIVES

The aim of this study was to compare chlamydial screening coverage estimates.

METHODS

We compared 9 estimates among women aged 15 to 25 years in Washington State, 2009. Four used Healthcare Effectiveness Data and Information System (HEDIS) procedures among Group Health enrollees. Separate HEDIS estimates assessed all enrollees and the subset of women who used services; for each group, separate estimates defined the sexually active population using HEDIS methods or National Survey of Family Growth (NSFG) data. Three indirect screening estimates used census and NSFG data to define the population's size and derived the number of tests performed by dividing the number of reported cases by test positivity defined using data from different laboratories, adjusted for repeat testing. A fourth indirect estimate was adjusted for reason for testing. A direct-indirect estimate combined data on the number of tests performed in reporting laboratories and an indirect estimate of tests performed elsewhere.

RESULTS

Healthcare Effectiveness Data and Information System procedures and NSFG data yielded similar estimates of the percentage of women who were sexually active (60% vs. 61%). Screening coverage estimated by HEDIS was higher among Group Health users (43.6%) than among all enrollees (34.2%). Indirect screening coverage estimates varied from 46.4% to 68.7%. The direct-indirect estimate, which included a direct measure of the number of tests performed to identify 52% of reported cases, was 57.6%.

CONCLUSIONS

Most sexually active women aged 15 to 25 years in Washington State were screened for chlamydia in 2009. Healthcare Effectiveness Data and Information System methods may underestimate screening coverage. Health departments can derive population-based coverage estimates using data from large laboratories.

Sexually transmitted infections screening at HIV treatment centers for MSM can be cost-effective

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.

Approximating optimal controls for networks when there are combinations of population-level and targeted measures available: chlamydia infection as a case-study

Using a modified one-dimensional model for the spread of an SIS disease on a network, we show that the behaviour of complex network simulations can be replicated with a simpler model. This model is then used to design optimal controls for use on the network, which would otherwise be unfeasible to obtain, resulting in information about how best to combine a population-level random intervention with one that is more targeted. This technique is used to minimise intervention costs over a short time interval with a target prevalence, and also to minimise prevalence with a specified budget. When applied to chlamydia, we find results consistent with previous work; that is maximising targeted control (contact tracing) is important to using resources effectively, while high-intensity bursts of population control (screening) are more effective than maintaining a high level of coverage.

Population movement can sustain STI prevalence in remote Australian indigenous communities

BACKGROUND

For almost two decades, chlamydia and gonorrhoea diagnosis rates in remote Indigenous communities have been up to 30 times higher than for non-Indigenous Australians. The high levels of population movement known to occur between remote communities may contribute to these high rates.

METHODS

We developed an individual-based computer simulation model to study the relationship between population movement and the persistence of gonorrhoea and chlamydia transmission within hypothetical remote communities.

RESULTS

Results from our model suggest that short-term population movement can facilitate gonorrhoea and chlamydia persistence in small populations. By fixing the number of short-term travellers in accordance with census data, we found that these STIs can persist if at least 20% of individuals in the population seek additional partners while away from home and if the time away from home is less than 21 days. Periodic variations in travel patterns can contribute to increased sustainable levels of infection. Expanding existing STI testing and treatment programs to cater for short-term travellers is shown to be ineffective due to their short duration of stay. Testing and treatment strategies tailored to movement patterns, such as encouraging travellers to seek testing and treatment upon return from travel, will likely be more effective.

CONCLUSION

High population mobility is likely to contribute to the high levels of STIs observed in remote Indigenous communities of Australia. More detailed data on mobility patterns and sexual behaviour of travellers will be invaluable for designing and assessing STI control programs in highly mobile communities.

Effects of population based screening for Chlamydia infections in the Netherlands limited by declining participation rates

Background

A large trial to investigate the effectiveness of population based screening for chlamydia infections was conducted in the Netherlands in 2008–2012. The trial was register based and consisted of four rounds of screening of women and men in the age groups 16–29 years in three regions in the Netherlands. Data were collected on participation rates and positivity rates per round. A modeling study was conducted to project screening effects for various screening strategies into the future.

Methods and Findings

We used a stochastic network simulation model incorporating partnership formation and dissolution, aging and a sexual life course perspective. Trends in baseline rates of chlamydia testing and treatment were used to describe the epidemiological situation before the start of the screening program. Data on participation rates was used to describe screening uptake in rural and urban areas. Simulations were used to project the effectiveness of screening on chlamydia prevalence for a time period of 10 years. In addition, we tested alternative screening strategies, such as including only women, targeting different age groups, and biennial screening. Screening reduced prevalence by about 1% in the first two screening rounds and leveled off after that. Extrapolating observed participation rates into the future indicated very low participation in the long run. Alternative strategies only marginally changed the effectiveness of screening. Higher participation rates as originally foreseen in the program would have succeeded in reducing chlamydia prevalence to very low levels in the long run.

Conclusions

Decreasing participation rates over time profoundly impact the effectiveness of population based screening for chlamydia infections. Using data from several consecutive rounds of screening in a simulation model enabled us to assess the future effectiveness of screening on prevalence. If participation rates cannot be kept at a sufficient level, the effectiveness of screening on prevalence will remain limited.

Investigating the potential public health benefit of jail-based screening and treatment programs for chlamydia

Observational studies have found mixed results on the impact of jail-based chlamydia screen-and-treat programs on community prevalence. In the absence of controlled trials or prospectively designed studies, dynamic mathematical models that incorporate movements in and out of jail and sexual contacts (including disease transmission) can provide useful information. We explored the impact of jail-based chlamydia screening on a hypothetical community's prevalence with a deterministic compartmental model focusing on heterosexual transmission. Parameter values were obtained from the published literature. Two analyses were conducted. One used national values (large community); the other used values reported among African Americans--the population with the highest incarceration rates and chlamydia burden (small community). A comprehensive sensitivity analysis was carried out. For the large-community analysis, chlamydia prevalence decreased by 13% (from 2.3% to 2.0%), and based on the ranges of parameter values (including screening coverage of 10%-100% and a postscreening treatment rate of 50%-100%) used in the sensitivity analysis, this decrease ranged from 0.1% to 58%. For the small-community analysis, chlamydia prevalence decreased by 54% (from 4.6% to 2.1%). Jail-based chlamydia screen-and-treat programs have the potential to reduce chlamydia prevalence in communities with high incarceration rates. However, the magnitude of this potential decrease is subject to considerable uncertainty.

Individual and population level effects of partner notification for Chlamydia trachomatis

Partner notification (PN or contact tracing) is an important aspect of treating bacterial sexually transmitted infections (STIs), such as Chlamydia trachomatis. It facilitates the identification of new infected cases that can be treated through individual case management. PN also acts indirectly by limiting onward transmission in the general population. However, the impact of PN, both at the level of individuals and the population, remains unclear. Since it is difficult to study the effects of PN empirically, mathematical and computational models are useful tools for investigating its potential as a public health intervention. To this end, we developed an individual-based modeling framework called Rstisim. It allows the implementation of different models of STI transmission with various levels of complexity and the reconstruction of the complete dynamic sexual partnership network over any time period. A key feature of this framework is that we can trace an individual's partnership history in detail and investigate the outcome of different PN strategies for C. trachomatis. For individual case management, the results suggest that notifying three or more partners from the preceding 18 months yields substantial numbers of new cases. In contrast, the successful treatment of current partners is most important for preventing re-infection of index cases and reducing further transmission of C. trachomatis at the population level. The findings of this study demonstrate the difference between individual and population level outcomes of public health interventions for STIs.

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

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.

Exploring short-term responses to changes in the control strategy for Chlamydia trachomatis

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.

Determinants of sexual network structure and their impact on cumulative network measures

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.

Uptake of regular chlamydia testing by U.S. women: a longitudinal study

BACKGROUND

Routine chlamydia screening is a recommended preventive intervention for sexually active women aged </=25 years in the U.S. but rates of regular uptake are not known.

PURPOSE

This study aimed to examine rates of annual chlamydia testing and factors associated with repeat testing in a population of U.S. women.

METHODS

Women aged 15-25 years at any time from January 1, 2002, to December 31, 2006 who were enrolled in 130 commercial health plans were included. Data relating to chlamydia tests were analyzed in 2009. Chlamydia testing rates (per 100 woman-years) by age and rates of repeated annual testing were estimated. Poisson regression was used to examine the effects of age and previous testing on further chlamydia testing within the observation period.

RESULTS

In total, 2,632,365 women were included. The chlamydia testing rate over the whole study period was 13.6 per 100 woman years after adjusting for age-specific sexual activity; 8.5 (95% CI=6.0, 12.3) per 100 woman-years in those aged 15 years; and 17.7 (95% CI=17.1, 18.9) in those aged 25 years. Among women enrolled for the entire 5-year study period, 25.9% had at least one test but only 0.1% had a chlamydia test every year. Women tested more than once and older women were more likely to be tested again in the observation period.

CONCLUSIONS

The low rates of regular annual chlamydia testing do not comply with national recommendations and would not be expected to have a major impact on the control of chlamydia infection at the population level.

Modeling secondary level of HIV contact tracing: its impact on HIV intervention in Cuba

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.

Evaluation design of a systematic, selective, internet-based, Chlamydia screening implementation in the Netherlands, 2008-2010: implications of first results for the analysis

BACKGROUND

A selective, systematic, Internet-based, Chlamydia Screening Implementation for 16 to 29-year-old residents started in three regions in the Netherlands in April 2008: in the cities of Amsterdam and Rotterdam and a more rural region, South Limburg. This paper describes the evaluation design and discusses the implications of the findings from the first screening round for the analysis. The evaluation aims to determine the effects of screening on the population prevalence of Chlamydia trachomatis after multiple screening rounds.

METHODS

A phased implementation or 'stepped wedge design' was applied by grouping neighbourhoods (hereafter: clusters) into three random, risk-stratified blocks (A, B and C) to allow for impact analyses over time and comparison of prevalences before and after one or two screening rounds. Repeated simulation of pre- and postscreening Chlamydia prevalences was used to predict the minimum detectable decline in prevalence. Real participation and positivity rates per region, block, and risk stratum (high, medium, and low community risk) from the 1st year of screening were used to substantiate predictions.

RESULTS

The results of the 1st year show an overall participation rate of 16% of 261,025 invitees and a positivity rate of 4.2%, with significant differences between regions and blocks. Prediction by simulation methods adjusted with the first-round results indicate that the effect of screening (minimal detectable difference in prevalence) may reach significance levels only if at least a 15% decrease in the Chlamydia positivity rate in the cities and a 25% decrease in the rural region after screening can be reached, and pre- and postscreening differences between blocks need to be larger.

CONCLUSIONS

With the current participation rates, the minimal detectable decline of Chlamydia prevalence may reach our defined significance levels at the regional level after the second screening round, but will probably not be significant between blocks of the stepped wedge design. Evaluation will also include other aspects and prediction models to obtain rational advice about future Chlamydia screening in the Netherlands.

Age- and gender-specific estimates of partnership formation and dissolution rates in the Seattle sex survey

PURPOSE

Partnership formation and dissolution rates are primary determinants of sexually transmitted infection (STI) transmission dynamics.

METHODS

The authors used data on persons' lifetime sexual experiences from a 2003-2004 random digit dialing survey of Seattle residents aged 18-39 years (N=1,194) to estimate age- and gender-specific partnership formation and dissolution rates. Partnership start and end dates were used to estimate participants' ages at the start of each partnership and partnership durations, and partnerships not enumerated in the survey were imputed.

RESULTS

Partnership formation peaked at age 19 at 0.9 (95% confidence interval [CI]: 0.76-1.04) partnerships per year and decreased to 0.1 to 0.2 after age 30 for women and peaked at age 20 at 1.4 (95% CI: 1.08-1.64) and declined to 0.5 after age 30 for men. Nearly one fourth (23.7%) of partnerships ended within 1 week and more than one half (51.2%) ended within 12 weeks. Most (63.5%) individuals 30 to 39 years of age had not formed a new sexual partnership in the past 3 years.

CONCLUSION

A large proportion of the heterosexual population is no longer at substantial STI risk by their early 30s, but similar analyses among high-risk populations may give insight into reasons for the profound disparities in STI rates across populations.

Mathematical Models in Infectious Disease Epidemiology

The idea that transmission and spread of infectious diseases follows laws that can be formulated in mathematical language is old. In 1766 Daniel Bernoulli published an article where he described the effects of smallpox variolation (a precursor of vaccination) on life expectancy using mathematical life table analysis (Dietz and Heesterbeek 2000). However, it was only in the twentieth century that the nonlinear dynamics of infectious disease transmission was really understood. In the beginning of that century there was much discussion about why an epidemic ended before all susceptibles were infected with hypotheses about changing virulence of the pathogen during the epidemic.

Gonorrhea and chlamydia in emergency departments: Screening, diagnosis, and treatment

Failure to screen sexually active adolescents and adults for gonorrhea and chlamydia at the time of acute care visits to urban emergency departments (ED) results in missed treatment opportunities for 38% to 82% of infected persons. The prevalence of gonorrhea and chlamydia infections among ED patients presenting with genitourinary or pregnancy-related complaints or providing urine specimens as part of routine medical care ranges from 4.3% to 16.4%. Notably, prevalence among general ED patients is similar (9.7%-14.3%). Due to the asymptomatic or nonspecific presentation of these infections, expanded screening is recommended to increase detection, treatment, and partner notification. A lower threshold of empiric treatment in the ED setting is recommended due to the difficulty and incompleteness of follow-up subsequent to ED discharge. Specific recommendations to improve the quality of ED care for sexually transmitted infections and to expand detection are provided.

Opportunistic screening of young men for urogenital Chlamydia trachomatis infection in general practice

Chlamydia trachomatis is a widespread, sexually transmitted infection causing pelvic inflammatory disease, infertility, ectopic pregnancy and chronic pelvic pain among women. Asymptomatic infections among men contribute significantly to maintaining the spread of the infection. In a 1-y intervention study in general practices we aimed to evaluate an opportunistic screening programme targeting 16-25-y-old men. When the young men saw their general practitioner (GP) for the first time during the intervention y, they were offered a test for C. trachomatis based on a first catch urine sample. Main outcome measures were percentage of tested men and prevalence of infection in the intervention practices compared with the test activity in the rest of the county during the intervention y and the y before. GPs in the intervention practices saw 617 (75.6%) of the 814 registered young men during the intervention period. Screening was offered to 300 (48.6%) and 219 (26.9% of the target population) accepted the invitation. The prevalence of infection among screened men was 5.0%. We conclude that opportunistic screening for urogenital C. trachomatis infection in general practice is feasible.

An epidemiological survey of chlamydial and gonococcal infections in a Canadian arctic community

BACKGROUND

Sexually transmitted infections are leading causes of morbidity for Canadian Aboriginal women. To date, very few initiatives have been successful in screening, treating, and limiting these infections among these populations.

OBJECTIVES

To evaluate the efficacy of universal screening, treatment and contact tracing as a means of capturing a more accurate count of chlamydia and gonorrhea prevalence and limiting transmission among Inuit communities.

METHODS

181 participants were screened for chlamydia and gonorrhea and interviewed in a cross-sectional survey (Aug-Sept/03). Information was collected on demographics, use of health services, sexual histories and STI knowledge among others. A random sample (n = 100) from the cross-sectional group was selected for the longitudinal cohort. Individuals were followed every two months post baseline for four visits (Oct/03-May/04). At each visit, participants were screened for chlamydia/gonorrhea. All positive cases and their partners were treated and contact tracing completed. Logistic Regression analysis and the McNemar Test of Correlated Proportions were used to analyze the data.

RESULTS

Overall, 35 cases of chlamydia were detected, with 21 detected at baseline and 14 during follow-up. The baseline prevalence was 11.6% in comparison with 2.7% that was previously estimated. No gonorrhea was detected. The strongest factor associated with a positive chlamydia was having recent STI (OR 9.82, CI: 2.70, 35.77).

CONCLUSIONS

Consistent with the literature, the results support the use of universal screening followed by prompt treatment and contact tracing in populations with greater than 10% chlamydia prevalence.

The program cost and cost-effectiveness of screening men for Chlamydia to prevent pelvic inflammatory disease in women

BACKGROUND

Because men transmit Chlamydia trachomatis to women, screening men to prevent pelvic inflammatory disease in women may be a viable strategy. However, the cost-effectiveness of this approach requires careful assessment.

METHODS

Data from a demonstration project and longitudinal study that examined screening men for chlamydia were applied to a compartment-based transmission model to estimate the cost-effectiveness of screening men for chlamydia compared with alternative interventions, including expanded screening of women and combining disease investigation specialist-provided partner notification with screening. Cases of pelvic inflammatory disease and quality-adjusted life years lost were the primary outcome measures. A male screening program that screened 1% of men in the population annually was modeled.

RESULTS

A program targeting high-risk men for screening (those with a larger number of partners in the previous year than the general population and a higher chlamydia prevalence) was cost saving compared with using equivalent program dollars to expand screening of lower-risk women. Combining partner notification with male screening was more effective than screening men alone. In sensitivity analyses, the male program was not always cost saving but averaged $10,520 per quality-adjusted life year saved over expanded screening of women.

CONCLUSIONS

Screening men can be a cost-effective alternative to screening women, but the men screened must have a relatively high prevalence compared with the women to whom screening would be expanded (under baseline assumptions, the prevalence in screened men was 86% higher than that of screened women). These modeling results suggest that programs targeting venues that have access to high-risk men can be effective tools in chlamydia prevention.

Acceptability of urine-based screening for Chlamydia trachomatis in asymptomatic young men: a systematic review

We performed a structured literature review of published studies from 2000-2007 that measured the acceptability and acceptance (uptake) of urine testing for C. trachomatis among asymptomatic men. Studies were categorized as three types: (a) non-STD clinic venues where men were approached in person and offered testing on site (urgent care clinics, freestanding clinics or health screening settings, corrections, community centers); (b) delivery of testing kits to men at their homes; and (c) qualitative measurement related to men's experience of screening. When offered in established nonhome-based settings (clinics, schools, corrections), acceptability and consequent uptake of testing by men is generally good (mid-60% range). However, acceptance rates even in these settings vary widely and are influenced by venue, provider, and a diversity of other factors. Acceptance of home-based testing invitations, including direct mailing of test kits, is considerably lower. Attitudinal characteristics of men who decline testing primarily include low self-perception of risk for asymptomatic infection and perceived inconvenience of providing test specimens. Given these findings, testing strategies targeting asymptomatic men in established community and clinic settings are most likely to yield relatively high acceptance rates. However, barriers to both implementation and uptake remain, even when such testing is free. Interventions to enhance uptake of testing in asymptomatic men should be developed and selected with underlying C. trachomatis population prevalence in mind.

Reproductive tract complications associated with Chlamydia trachomatis infection in US Air Force males within 4 years of testing

BACKGROUND

Chlamydia trachomatis (CT) is a common sexually transmitted infection for which young, sexually active persons are at highest risk. Health consequences such as orchitis/epididymitis, prostatitis, infertility, and urethral stricture have been described among CT-infected males, although not all of these are indisputably linked to CT. Current literature lacks population-based studies needed to examine these associations on a larger scale, to evaluate the true risk of developing complications after a CT infection. The US Air Force contains a large population of young, sexually active males, making it suitable for conducting such a study.

METHODS

We conducted a retrospective cohort study between 2001 and 2005 comparing the incidence of orchitis/epididymitis, prostatitis, infertility, and urethral stricture among male Air Force members with and without prior CT infections. Cumulative incidence rates were calculated and Cox proportional hazard models were generated to evaluate the risk of developing complications and to adjust for potential confounders.

RESULTS

Among 17,764 men enrolled in the study, 913 (5.14%) experienced a reproductive tract outcome. Among CT-positive men, cumulative incidences of orchitis/epididymitis, prostatitis, infertility, and urethral stricture were 4.28%, 1.41%, 1.27%, and 0.13%, respectively. Orchitis/epididymitis [Hazard ratio (HR) = 1.38 (1.13-1.70)] and "any" outcome [HR = 1.37 (1.16-1.61)] were positively associated with CT; infertility was marginally associated [HR = 1.36 (0.93-2.00)].

CONCLUSIONS

Overall, the burden of reproductive health outcomes among Air Force males is small. Significant associations were observed between CT and both orchitis/epididymitis and any outcome; a larger cohort or longer follow-up may have detected a significant association between CT and infertility.

Chlamydia screening--Australia should strive to achieve what others have not

Chlamydia screening programs overseas have failed to reduce chlamydia prevalence despite screening 20%-30% of young sexually active women. The Australian federal government announced in 2005 that it would provide $12.5 million for chlamydia control. Policymakers must look to chlamydia screening programs in other countries to learn from their experience. Australia has an excellent primary health care system and a strong track record in establishing highly successful public health programs. This experience places it in a strong position to design and implement an innovative chlamydia screening program to reduce chlamydia prevalence.

Increasing Chlamydia Positivity in Women Screened in Family Planning Clinics: Do We Know Why?

OBJECTIVE

Following a 9-year 60% decline, chlamydia positivity increased 46% from 1997 through 2004 among young sexually active women screened in Region X family planning clinics. The objective of this analysis was to systematically examine the influences of risk factors, changing laboratory test methods, and interclinic variability on chlamydia positivity during this period.

STUDY DESIGN

We analyzed data from 520,512 chlamydia tests from women aged 15 to 24 years screened in 125 family planning clinics. Multivariate logistic regression modeling was used to adjust the annual risk of chlamydia for the demographic, clinical, and sexual risk behavior characteristics associated with infection and for the increasing use of more sensitive laboratory test methods. A generalized linear mixed model was used to adjust for interclinic variability.

RESULTS

We found a significant 5% annual increase in the risk of chlamydia even after adjusting for risk factors including laboratory test characteristics (odds ratio 1.05, 95% confidence interval: 1.04, 1.06). Variability among the clinics where screening occurred did not account for the increase.

CONCLUSIONS

Based on a review of all available data, we concluded that there was a true increase in chlamydia positivity over the 8-year period.

Cost effectiveness of home based population screening for Chlamydia trachomatis in the UK: economic evaluation of chlamydia screening studies (ClaSS) project

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.