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Hawley DM, Pérez-Umphrey AA, Adelman JS, Fleming-Davies AE, Garrett-Larsen J, Geary SJ, Childs LM, Langwig KE. Prior exposure to pathogens augments host heterogeneity in susceptibility and has key epidemiological consequences. PLoS Pathog 2024; 20:e1012092. [PMID: 39231171 PMCID: PMC11404847 DOI: 10.1371/journal.ppat.1012092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2024] [Revised: 09/16/2024] [Accepted: 08/19/2024] [Indexed: 09/06/2024] Open
Abstract
Pathogen epidemics are key threats to human and wildlife health. Across systems, host protection from pathogens following initial exposure is often incomplete, resulting in recurrent epidemics through partially-immune hosts. Variation in population-level protection has important consequences for epidemic dynamics, but how acquired protection influences inter-individual heterogeneity in susceptibility and its epidemiological consequences remains understudied. We experimentally investigated whether prior exposure (none, low-dose, or high-dose) to a bacterial pathogen alters host heterogeneity in susceptibility among songbirds. Hosts with no prior pathogen exposure had little variation in protection, but heterogeneity in susceptibility was significantly augmented by prior pathogen exposure, with the highest variability detected in hosts given high-dose prior exposure. An epidemiological model parameterized with experimental data found that heterogeneity in susceptibility from prior exposure more than halved epidemic sizes compared with a homogeneous population with identical mean protection. However, because infection-induced mortality was also greatly reduced in hosts with prior pathogen exposure, reductions in epidemic size were smaller than expected in hosts with prior exposure. These results highlight the importance of variable protection from prior exposure and/or vaccination in driving population-level heterogeneity and epidemiological dynamics.
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Affiliation(s)
- Dana M Hawley
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virgina, United States of America
| | - Anna A Pérez-Umphrey
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virgina, United States of America
| | - James S Adelman
- Department of Biological Sciences, University of Memphis, Memphis, Tennessee, United States of America
| | | | - Jesse Garrett-Larsen
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virgina, United States of America
| | - Steven J Geary
- Department of Pathobiology & Veterinary Science, University of Connecticut, Storrs, Connecticut, United States of America
| | - Lauren M Childs
- Department of Mathematics and Virginia Tech Center for the Mathematics of Biosystems, Virginia Tech, Blacksburg, Virginia, United States of America
| | - Kate E Langwig
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virgina, United States of America
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2
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Hawley DM, Pérez-Umphrey AA, Adelman JS, Fleming-Davies AE, Garrett-Larsen J, Geary SJ, Childs LM, Langwig KE. Prior exposure to pathogens augments host heterogeneity in susceptibility and has key epidemiological consequences. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.05.583455. [PMID: 38496428 PMCID: PMC10942282 DOI: 10.1101/2024.03.05.583455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/19/2024]
Abstract
Pathogen epidemics are key threats to human and wildlife health. Across systems, host protection from pathogens following initial exposure is often incomplete, resulting in recurrent epidemics through partially-immune hosts. Variation in population-level protection has important consequences for epidemic dynamics, but how acquired protection influences inter-individual heterogeneity in susceptibility and its epidemiological consequences remains understudied. We experimentally investigated whether prior exposure (none, low-dose, or high-dose) to a bacterial pathogen alters host heterogeneity in susceptibility among songbirds. Hosts with no prior pathogen exposure had little variation in protection, but heterogeneity in susceptibility was significantly augmented by prior pathogen exposure, with the highest variability detected in hosts given high-dose prior exposure. An epidemiological model parameterized with experimental data found that heterogeneity in susceptibility from prior exposure more than halved epidemic sizes compared with a homogeneous population with identical mean protection. However, because infection-induced mortality was also greatly reduced in hosts with prior pathogen exposure, reductions in epidemic size were smaller than expected in hosts with prior exposure. These results highlight the importance of variable protection from prior exposure and/or vaccination in driving population-level heterogeneity and epidemiological dynamics.
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Affiliation(s)
- Dana M Hawley
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA
| | | | - James S Adelman
- Department of Biological Sciences, University of Memphis, Memphis, TN, USA
| | | | | | - Steven J Geary
- Department of Pathobiology & Veterinary Science, University of Connecticut, Storrs, CT, USA
| | - Lauren M Childs
- Department of Mathematics and Virginia Tech Center for Mathematics of Biosystems, Virginia Tech, Blacksburg, VA, USA
| | - Kate E Langwig
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA
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3
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Marks SM, Self JL, Venkatappa T, Wolff MB, Hopkins PB, Augustine RJ, Khan A, Schwartz NG, Schmit KM, Morris SB. Diagnosis, Treatment, and Prevention of Tuberculosis Among People Experiencing Homelessness in the United States: Current Recommendations. Public Health Rep 2023; 138:896-907. [PMID: 36703605 PMCID: PMC10576477 DOI: 10.1177/00333549221148173] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
OBJECTIVE Tuberculosis (TB) is a public health problem, especially among people experiencing homelessness (PEH). The Advisory Council for the Elimination of Tuberculosis issued recommendations in 1992 for TB prevention and control among PEH. Our goal was to provide current guidelines and information in one place to inform medical and public health providers and TB programs on TB incidence, diagnosis, and treatment among PEH. METHODS We reviewed and synthesized diagnostic and treatment recommendations for TB disease and latent TB infection (LTBI) as of 2022 and information after 1992 on the magnitude of homelessness in the United States, the incidence of TB among PEH, the role of public health departments in TB case management among PEH, and recently published evidence. RESULTS In 2018, there were 1.45 million estimated PEH in the United States. During the past 2 decades, the incidence of TB was >10 times higher and the prevalence of LTBI was 7 to 20 times higher among PEH than among people not experiencing homelessness. TB outbreaks were common in overnight shelters. Permanent housing for PEH and the use of rapid TB diagnostic tests, along with isolation and treatment, reduced TB exposure among PEH. The use of direct observation enhanced treatment adherence among PEH, as did involvement of social workers to help secure shelter, food, safety, and treatment for comorbidities, especially HIV and substance use disorders. Testing and treatment for LTBI prevented progression to TB disease, and shorter LTBI regimens helped improve adherence. Federal agencies and the National Health Care for the Homeless Council have helpful resources. CONCLUSION Improvements in TB diagnosis, treatment, and prevention among PEH are possible by following existing recommendations and using client-centered approaches.
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Affiliation(s)
- Suzanne M. Marks
- Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Julie L. Self
- Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Thara Venkatappa
- Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Marilyn B. Wolff
- Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Peri B. Hopkins
- Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Ryan J. Augustine
- Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Awal Khan
- Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Noah G. Schwartz
- Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Kristine M. Schmit
- Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Sapna Bamrah Morris
- Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA
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Chen Q, Yu S, Rui J, Guo Y, Yang S, Abudurusuli G, Yang Z, Liu C, Luo L, Wang M, Lei Z, Zhao Q, Gavotte L, Niu Y, Frutos R, Chen T. Transmissibility of tuberculosis among students and non-students: an occupational-specific mathematical modelling. Infect Dis Poverty 2022; 11:117. [PMID: 36461098 PMCID: PMC9716537 DOI: 10.1186/s40249-022-01046-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Accepted: 11/17/2022] [Indexed: 12/05/2022] Open
Abstract
BACKGROUND Recently, despite the steady decline in the tuberculosis (TB) epidemic globally, school TB outbreaks have been frequently reported in China. This study aimed to quantify the transmissibility of Mycobacterium tuberculosis (MTB) among students and non-students using a mathematical model to determine characteristics of TB transmission. METHODS We constructed a dataset of reported TB cases from four regions (Jilin Province, Xiamen City, Chuxiong Prefecture, and Wuhan City) in China from 2005 to 2019. We classified the population and the reported cases under student and non-student groups, and developed two mathematical models [nonseasonal model (Model A) and seasonal model (Model B)] based on the natural history and transmission features of TB. The effective reproduction number (Reff) of TB between groups were calculated using the collected data. RESULTS During the study period, data on 456,423 TB cases were collected from four regions: students accounted for 6.1% of cases. The goodness-of-fit analysis showed that Model A had a better fitting effect (P < 0.001). The average Reff of TB estimated from Model A was 1.68 [interquartile range (IQR): 1.20-1.96] in Chuxiong Prefecture, 1.67 (IQR: 1.40-1.93) in Xiamen City, 1.75 (IQR: 1.37-2.02) in Jilin Province, and 1.79 (IQR: 1.56-2.02) in Wuhan City. The average Reff of TB in the non-student population was 23.30 times (1.65/0.07) higher than that in the student population. CONCLUSIONS The transmissibility of MTB remains high in the non-student population of the areas studied, which is still dominant in the spread of TB. TB transmissibility from the non-student-to-student-population had a strong influence on students. Specific interventions, such as TB screening, should be applied rigorously to control and to prevent TB transmission among students.
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Affiliation(s)
- Qiuping Chen
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China
- CIRAD, URM 17, Intertryp, Montpellier, France
- Université de Montpellier, Montpellier, France
| | - Shanshan Yu
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Jia Rui
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China
- CIRAD, URM 17, Intertryp, Montpellier, France
- Université de Montpellier, Montpellier, France
| | - Yichao Guo
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Shiting Yang
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Guzainuer Abudurusuli
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Zimei Yang
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Chan Liu
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Li Luo
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Mingzhai Wang
- Xiamen Center for Disease Control and Prevention, Xiamen, Fujian, People's Republic of China
| | - Zhao Lei
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Qinglong Zhao
- Jilin Provincial Center for Disease Control and Prevention, Changchun, Jilin, People's Republic of China
| | | | - Yan Niu
- Chinese Center for Disease Control and Prevention, 155 Changbai Road, Changping District, Beijing, China.
| | | | - Tianmu Chen
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, Xiamen, Fujian, People's Republic of China.
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Coleman M, Martinez L, Theron G, Wood R, Marais B. Mycobacterium tuberculosis Transmission in High-Incidence Settings-New Paradigms and Insights. Pathogens 2022; 11:1228. [PMID: 36364978 PMCID: PMC9695830 DOI: 10.3390/pathogens11111228] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2022] [Revised: 10/20/2022] [Accepted: 10/21/2022] [Indexed: 12/01/2023] Open
Abstract
Tuberculosis has affected humankind for thousands of years, but a deeper understanding of its cause and transmission only arose after Robert Koch discovered Mycobacterium tuberculosis in 1882. Valuable insight has been gained since, but the accumulation of knowledge has been frustratingly slow and incomplete for a pathogen that remains the number one infectious disease killer on the planet. Contrast that to the rapid progress that has been made in our understanding SARS-CoV-2 (the cause of COVID-19) aerobiology and transmission. In this Review, we discuss important historical and contemporary insights into M. tuberculosis transmission. Historical insights describing the principles of aerosol transmission, as well as relevant pathogen, host and environment factors are described. Furthermore, novel insights into asymptomatic and subclinical tuberculosis, and the potential role this may play in population-level transmission is discussed. Progress towards understanding the full spectrum of M. tuberculosis transmission in high-burden settings has been hampered by sub-optimal diagnostic tools, limited basic science exploration and inadequate study designs. We propose that, as a tuberculosis field, we must learn from and capitalize on the novel insights and methods that have been developed to investigate SARS-CoV-2 transmission to limit ongoing tuberculosis transmission, which sustains the global pandemic.
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Affiliation(s)
- Mikaela Coleman
- WHO Collaborating Centre for Tuberculosis and the Sydney Institute for Infectious Diseases, The University of Sydney, Sydney 2006, Australia
- Tuberculosis Research Program, Centenary Institute, The University of Sydney, Sydney 2050, Australia
| | - Leonardo Martinez
- Department of Epidemiology, Boston University School of Public Health, Boston, MA 02118, USA
| | - Grant Theron
- DSI-NRF Centre of Excellence for Biomedical Tuberculosis Research, South African Medical Research Council Centre for Tuberculosis Research, Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town 7602, South Africa
| | - Robin Wood
- Desmond Tutu Health Foundation and Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town 7700, South Africa
| | - Ben Marais
- WHO Collaborating Centre for Tuberculosis and the Sydney Institute for Infectious Diseases, The University of Sydney, Sydney 2006, Australia
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Neighborhood Characteristics and Racial Disparities in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Seropositivity in Pregnancy. Obstet Gynecol 2022; 139:1018-1026. [PMID: 35675599 DOI: 10.1097/aog.0000000000004791] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Accepted: 03/03/2022] [Indexed: 11/26/2022]
Abstract
OBJECTIVE To quantify the extent to which neighborhood characteristics contribute to racial and ethnic disparities in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seropositivity in pregnancy. METHODS This cohort study included pregnant patients who presented for childbirth at two hospitals in Philadelphia, Pennsylvania from April 13 to December 31, 2020. Seropositivity for SARS-CoV-2 was determined by measuring immunoglobulin G and immunoglobulin M antibodies by enzyme-linked immunosorbent assay in discarded maternal serum samples obtained for clinical purposes. Race and ethnicity were self-reported and abstracted from medical records. Patients' residential addresses were geocoded to obtain three Census tract variables: community deprivation, racial segregation (Index of Concentration at the Extremes), and crowding. Multivariable mixed effects logistic regression models and causal mediation analyses were used to quantify the extent to which neighborhood variables may explain racial and ethnic disparities in seropositivity. RESULTS Among 5,991 pregnant patients, 562 (9.4%) were seropositive for SARS-CoV-2. Higher seropositivity rates were observed among Hispanic (19.3%, 104/538) and Black (14.0%, 373/2,658) patients, compared with Asian (3.2%, 13/406) patients, White (2.7%, 57/2,133) patients, and patients of another race or ethnicity (5.9%, 15/256) (P<.001). In adjusted models, per SD increase, deprivation (adjusted odds ratio [aOR] 1.16, 95% CI 1.02-1.32) and crowding (aOR 1.15, 95% CI 1.05-1.26) were associated with seropositivity, but segregation was not (aOR 0.90, 95% CI 0.78-1.04). Mediation analyses revealed that crowded housing may explain 6.7% (95% CI 2.0-14.7%) of the Hispanic-White disparity and that neighborhood deprivation may explain 10.2% (95% CI 0.5-21.1%) of the Black-White disparity. CONCLUSION Neighborhood deprivation and crowding were associated with SARS-CoV-2 seropositivity in pregnancy in the prevaccination era and may partially explain high rates of SARS-CoV-2 seropositivity among Black and Hispanic patients. Investing in structural neighborhood improvements may reduce inequities in viral transmission.
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7
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Abstract
Pulmonary granulomas are widely considered the epicenters of the immune response to Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). Recent animal studies have revealed factors that either promote or restrict TB immunity within granulomas. These models, however, typically ignore the impact of preexisting immunity on cellular organization and function, an important consideration because most TB probably occurs through reinfection of previously exposed individuals. Human postmortem research from the pre-antibiotic era showed that infections in Mtb-naïve individuals (primary TB) versus those with prior Mtb exposure (postprimary TB) have distinct pathologic features. We review recent animal findings in TB granuloma biology, which largely reflect primary TB. We also discuss our current understanding of postprimary TB lesions, about which much less is known. Many knowledge gaps remain, particularly regarding how preexisting immunity shapes granuloma structure and local immune responses at Mtb infection sites. Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Sara B. Cohen
- Seattle Children's Research Institute, Seattle, Washington, USA
| | - Benjamin H. Gern
- Seattle Children's Research Institute, Seattle, Washington, USA
- Department of Pediatrics, University of Washington, Seattle, Washington, USA
| | - Kevin B. Urdahl
- Seattle Children's Research Institute, Seattle, Washington, USA
- Department of Pediatrics, University of Washington, Seattle, Washington, USA
- Department of Immunology, University of Washington, Seattle, Washington, USA
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8
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Baik Y, Modongo C, Moonan PK, Click ES, Tobias JL, Boyd R, Finlay A, Oeltmann JE, Shin SS, Zetola NM. Possible Transmission Mechanisms of Mixed Mycobacterium tuberculosis Infection in High HIV Prevalence Country, Botswana. Emerg Infect Dis 2021; 26:953-960. [PMID: 32310078 PMCID: PMC7181944 DOI: 10.3201/eid2605.191638] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Tuberculosis caused by concurrent infection with multiple Mycobacteriumtuberculosis strains (i.e., mixed infection) challenges clinical and epidemiologic paradigms. We explored possible transmission mechanisms of mixed infection in a population-based, molecular epidemiology study in Botswana during 2012–2016. We defined mixed infection as multiple repeats of alleles at >2 loci within a discrete mycobacterial interspersed repetitive unit–variable-number tandem-repeat (MIRU-VNTR) result. We compared mixed infection MIRU-VNTR results with all study MIRU-VNTR results by considering all permutations at each multiple allele locus; matched MIRU-VNTR results were considered evidence of recently acquired strains and nonmatched to any other results were considered evidence of remotely acquired strains. Among 2,051 patients, 34 (1.7%) had mixed infection, of which 23 (68%) had recently and remotely acquired strains. This finding might support the mixed infection mechanism of recent transmission and simultaneous remote reactivation. Further exploration is needed to determine proportions of transmission mechanisms in settings where mixed infections are prevalent.
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9
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Nardell EA. Time to Revise Our Tuberculosis Infection-Latency-Disease Model in High-burden Settings. Clin Infect Dis 2021; 72:2016-2017. [PMID: 32584981 DOI: 10.1093/cid/ciaa866] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Accepted: 06/22/2020] [Indexed: 11/13/2022] Open
Affiliation(s)
- Edward A Nardell
- Brigham & Women's Hospital, Division of Global Health Equity, Boston, MA, USA.,Harvard Medical School, Department of Global Health and Social Medicine, Boston, MA, USA
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10
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Baral S, Bond A, Boozary A, Bruketa E, Elmi N, Freiheit D, Ghosh SM, Goyer ME, Orkin AM, Patel J, Richter T, Robertson A, Sutherland C, Svoboda T, Turnbull J, Wong A, Zhu A. Seeking shelter: homelessness and COVID-19. Facets (Ott) 2021. [DOI: 10.1139/facets-2021-0004] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Those experiencing homelessness in Canada are impacted inequitably by COVID-19 due to their increased exposure, vulnerability of environment and medical comorbidities, and their lack of access to preventive care and treatment in the context of the pandemic. In shelter environments one is unable to effectively physically distance, maintain hygiene, obtain a test, or isolate. As a result, unique strategies are required for this population to protect them and those who serve them. Recommendations are provided to reduce or prevent further negative consequences from the COVID-19 pandemic for people experiencing homelessness. These recommendations were informed by a systematic review of the literature, as well as a jurisdictional scan. Where evidence did not exist, expert consensus from key providers and those experiencing homelessness throughout Canada was included. These recommendations recognize the need for short-term interventions to mitigate the immediate risk to this community, including coordination of response, appropriate precautions and protective equipment, reducing congestion, cohorting, testing, case and contact management strategies, dealing with outbreaks, isolation centres, and immunization. Longer-term recommendations are also provided with a view to ending homelessness by addressing the root causes of homelessness and by the provision of adequate subsidized and supportive housing through a Housing First strategy. It is imperative that meaningful changes take place now in how we serve those experiencing homelessness and how we mitigate specific vulnerabilities. These recommendations call for intersectoral, collaborative engagement to work for solutions targeted towards protecting the most vulnerable within our community through both immediate actions and long-term planning to eliminate homelessness.
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Affiliation(s)
- Stefan Baral
- Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
- Inner City Health Associates, Toronto, ON M5C 1K6, Canada
| | - Andrew Bond
- Inner City Health Associates, Toronto, ON M5C 1K6, Canada
- Department of Family and Community Medicine, University of Toronto, Toronto, ON M5G 1V7, Canada
| | - Andrew Boozary
- Population Health and Social Medicine, University Health Network, Toronto, ON M5G 2C4, Canada
- University of Toronto, Toronto, ON M5S 1A8, Canada
- Columbia University, New York, NY 10032, USA
| | - Eva Bruketa
- Queen’s University, Kingston, ON K7L 3N6, Canada
| | - Nika Elmi
- Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
| | | | - S. Monty Ghosh
- Department of General Internal Medicine & Neurology, University of Alberta, Edmonton, AB T6G 2G3, Canada
- Department of Medicine & Psychiatry, University of Calgary, Calgary, AB T2N 1N4, Canada
| | - Marie Eve Goyer
- Family Medicine and Emergency Department, University of Montréal, Montréal, QC H3T 1J4, Canada
| | - Aaron M. Orkin
- Inner City Health Associates, Toronto, ON M5C 1K6, Canada
- Department of Family and Community Medicine, University of Toronto, Toronto, ON M5G 1V7, Canada
- Department of Emergency Medicine, St. Joseph’s Health Centre, Toronto, ON M6R 1B5, Canada
- Department of Emergency Medicine, Humber River Hospital, Toronto, ON M3M 0B2, Canada
| | - Jamie Patel
- Faculty of Community Services, Ryerson University, Toronto, ON M5B 2K3, Canada
| | - Tim Richter
- Canadian Alliance to End Homelessness, Calgary, AB T3H 0N8, Canada
| | - Angela Robertson
- Parkdale Queen West Community Health Centre, Toronto, ON M6K 1L2, Canada
| | - Christy Sutherland
- PHS Community Services Society, Vancouver, BC V6A 1M9, Canada
- Department of Family Medicine, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Tomislav Svoboda
- Department of Family and Community Medicine, University of Toronto, Toronto, ON M5G 1V7, Canada
| | - Jeffrey Turnbull
- University of Ottawa, Ottawa, ON K1N 6N5, Canada
- Ottawa Inner City Health, Ottawa, ON K1N 5N7, Canada
| | - Alexander Wong
- Department of Medicine, University of Saskatchewan, Regina, SK S4T 0H8, Canada
| | - Alice Zhu
- University of Toronto, Toronto, ON M5S 1A8, Canada
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11
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Donald PR, Diacon AH, Thee S. Anton Ghon and His Colleagues and Their Studies of the Primary Focus and Complex of Tuberculosis Infection and Their Relevance for the Twenty-First Century. Respiration 2020; 100:557-567. [PMID: 33321506 DOI: 10.1159/000509522] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2020] [Accepted: 06/16/2020] [Indexed: 11/19/2022] Open
Abstract
Anton Ghon is well known in the field of childhood tuberculosis, and the tuberculosis primary focus and complex are frequently called the Ghon focus and complex; this is largely the result of the wide publication of the English translation of his monograph "Der primäre Lungenherd bei der Tuberkulose der Kinder." Ghon's studies are frequently quoted, but precise details of his monograph are neglected, his results often misquoted, and his later publications virtually unknown. This review highlights aspects of Ghon's anatomical pathology studies in children and adults not necessarily dying of tuberculosis but with signs of tuberculosis infection. Ghon found a single primary tuberculosis focus in approximately 80% of tuberculosis-infected children situated close to the pleura in two-thirds of cases. Cavitation of the focus was common, and lymphatic spread involved lymph nodes in the abdomen and neck in many children. Studies amongst adults and children frequently found the healed primary tuberculosis focus to be completely calcified without histological signs of tuberculosis activity; however, particularly in the presence of pulmonary tuberculosis, histological signs of tuberculosis activity were often found in the lymph nodes of the angulus venosus, despite apparent healing with extensive calcification. Both earlier studies and more recent investigations, with molecular biological tools, unavailable to Ghon and earlier researchers, have confirmed the presence of viable mycobacteria in apparently normal or healed thoracic nodes and also found molecular biological indications of viable mycobacteria in these nodes. As suggested by Ghon, lympho-haematogenous spread of tuberculosis may be more common than is usually appreciated.
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Affiliation(s)
- Peter R Donald
- Department of Paediatrics and Child Health, Desmond Tutu TB Centre, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa, .,Task Applied Science, Bellville, South Africa,
| | - Andreas H Diacon
- Department of Medicine, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - Stephanie Thee
- Department of Pediatrics, Division of Pneumonology and Immunology with Intensive Medicine, Charité Universitätsmedizin, Berlin, Germany
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12
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Eddy JJ, Gadani KM, Tibbs A, Bernardo J, Cochran J, White LF, Horsburgh CR, Jacobson KR. Increasing Drug Resistance Among Persons With Tuberculosis in Massachusetts, 2009-2018. Open Forum Infect Dis 2020; 7:ofaa300. [PMID: 32855987 PMCID: PMC7444736 DOI: 10.1093/ofid/ofaa300] [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: 04/25/2020] [Accepted: 07/15/2020] [Indexed: 11/14/2022] Open
Abstract
We examined Massachusetts tuberculosis surveillance data from to 2009 to 2018. Of 1533 culture-confirmed cases, 190 (12.4%) demonstrated resistance to isoniazid including 32 (2.1%) with rifampin resistance. In multivariable analysis, isoniazid resistance increased significantly over time (per-year odds ratio = 1.07, 95% confidence interval = 1.01-1.13, P = .018) and was associated with younger age, foreign birth, and prior tuberculosis treatment.
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Affiliation(s)
- Jared J Eddy
- Section of Infectious Diseases, Boston University School of Medicine, Boston, Massachusetts, USA
| | - Kavita M Gadani
- Massachusetts Department of Public Health, Boston, Massachusetts, USA
| | - Andrew Tibbs
- Division of Global Populations, Massachusetts Department of Public Health, Boston, Massachusetts, USA
| | - John Bernardo
- Division of Global Populations and Infectious Disease Prevention, Massachusetts Department of Public Health, Boston, Massachusetts, USA.,Boston University School of Medicine, Boston, Massachusetts, USA
| | - Jennifer Cochran
- Division of Global Populations and Infectious Disease Prevention, Massachusetts Department of Public Health, Boston, Massachusetts, USA
| | - Laura F White
- Department of Biostatistics, Boston University, Boston, Massachusetts, USA
| | - C Robert Horsburgh
- Epidemiology, Biostatistics, Global Health and Medicine, Boston University Schools of Public Health and Medicine, Boston, Massachusetts, USA
| | - Karen R Jacobson
- Section of Infectious Diseases, Boston University School of Medicine, Boston, Massachusetts, USA
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13
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Nathavitharana RR, Lederer P, Tierney DB, Nardell E. Treatment as prevention and other interventions to reduce transmission of multidrug-resistant tuberculosis. Int J Tuberc Lung Dis 2020; 23:396-404. [PMID: 31064617 DOI: 10.5588/ijtld.18.0276] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Drug-resistant tuberculosis (DR-TB) represents a major programmatic challenge at the national and global levels. Only ∼30% of patients with multidrug-resistant TB (MDR-TB) were diagnosed, and ∼25% were initiated on treatment for MDR-TB in 2016. Increasing evidence now points towards primary transmission of DR-TB, rather than inadequate treatment, as the main driver of the DR-TB epidemic. The cornerstone of DR-TB transmission prevention should be earlier diagnosis and prompt initiation of effective treatment for all patients with DR-TB. Despite the extensive scale-up of Xpert® MTB/RIF testing, major implementation barriers continue to limit its impact. Although there is longstanding evidence in support of the rapid impact of treatment on patient infectiousness, delays in the initiation of effective DR-TB treatment persist, resulting in ongoing transmission. However, it is also imperative to address the burden of latent drug-resistant tuberculous infection because it is estimated that many DR-TB patients will become infectious before seeking care and encounter various diagnostic delays before treatment. Addressing latent DR-TB primarily consists of identifying, treating and following the contacts of patients with MDR-TB, typically through household contact evaluation. Adjunctive measures, such as improved ventilation and use of germicidal ultraviolet technology can further reduce TB transmission in high-risk congregate settings. Although many gaps remain in our biological understanding of TB transmission, implementation barriers to early diagnosis and rapid initiation of effective DR-TB treatment can and must be overcome if we are to impact DR-TB incidence in the short and long term.
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Affiliation(s)
- R R Nathavitharana
- Division of Infectious Diseases, Beth Israel Deaconess Medical Center, Boston, Massachusetts
| | - P Lederer
- Section of Infectious Diseases, Boston Medical Center, Boston, Massachusetts
| | - D B Tierney
- Division of Global Health Equity, Brigham and Women's Hospital, Boston, Massachusetts, USA
| | - E Nardell
- Division of Global Health Equity, Brigham and Women's Hospital, Boston, Massachusetts, USA
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Ssebuliba DM, Ouifki R. Effect of mixed infection on TB dynamics. INT J BIOMATH 2019. [DOI: 10.1142/s179352451950061x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Poor living conditions, overcrowding and strain diversity are some of the factors that influence mixed infection in Tuberculosis (TB) at the population level. We formulate a mathematical model for mixed infection in TB using nonlinear ordinary differential equations where such factors were represented as probabilities of acquiring mixed infection. A qualitative analysis of the model shows that it exhibits multiple endemic equilibria and backward bifurcation for certain parameter values. The reactivation rate and transmission rate of individuals with mixed infection were of importance as well as the probabilities for latent individuals to acquire mixed infection. We calculate the prevalence of mixed infection from the model and the effect of mixed infection on TB incidence, TB prevalence and Mycobacterium tuberculosis (MTB) infection rate. Numerical simulations show that mixed infection may explain high TB incidences in areas which have a high strain diversity, poor living conditions and are overcrowded even without HIV.
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Affiliation(s)
- Doreen Mbabazi Ssebuliba
- Faculty of Science, Kabale University, P. O. Box 317, Kabale, Uganda
- South African Centre for Epidemiological Modelling, and Analysis, 19 Jonkershoek, Mostertdrift, Stellenbosch, 7600, Cape Town, Western Cape, South Africa
| | - Rachid Ouifki
- South African Centre for Epidemiological Modelling, and Analysis, 19 Jonkershoek, Mostertdrift, Stellenbosch, 7600, Cape Town, Western Cape, South Africa
- Department of Mathematics and Applied Mathematics, University of Pretoria, Private bag X20, Hatfield, 0028 Pretoria, South Africa
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Escombe AR, Ticona E, Chávez-Pérez V, Espinoza M, Moore DAJ. Improving natural ventilation in hospital waiting and consulting rooms to reduce nosocomial tuberculosis transmission risk in a low resource setting. BMC Infect Dis 2019; 19:88. [PMID: 30683052 PMCID: PMC6347752 DOI: 10.1186/s12879-019-3717-9] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Accepted: 01/11/2019] [Indexed: 12/03/2022] Open
Abstract
Background TB transmission in healthcare facilities is an important public health problem, especially in the often-overcrowded settings of HIV treatment scale-up. The problem is compounded by the emergence of drug resistant TB. Natural ventilation is a low-cost environmental control measure for TB infection control where climate permits that is suited to many different areas in healthcare facilities. There are no published data on the effect of simple structural modifications to existing hospital infrastructure to improve natural ventilation and reduce the risk of nosocomial TB transmission. The purpose of this study was to measure the effect of simple architectural modifications to existing hospital waiting and consulting rooms in a low resource setting on (a) improving natural ventilation and (b) reducing modelled TB transmission risk. Methods Room ventilation was measured pre- and post-modification using a carbon dioxide tracer-gas technique in four waiting rooms and two consulting rooms in two hospitals in Lima, Peru. Modifications included additional windows for cross-ventilation (n = 2 rooms); removing glass from unopenable windows (n = 2); creation of an open skylight (n = 1); re-building a waiting-room in the open air (n = 1). Changes in TB transmission risk for waiting patients, or healthcare workers in consulting rooms, were estimated using mathematical modelling. Results As a result of the infrastructure modifications, room ventilation in the four waiting rooms increased from mean 5.5 to 15; 11 to 16; 10 to 17; and 9 to 66 air-changes/hour respectively; and in the two consulting rooms from mean 3.6 to 17; and 2.7 to 12 air-changes/hour respectively. There was a median 72% reduction (inter-quartile range 51–82%) in calculated TB transmission risk for healthcare workers or waiting patients. The modifications cost <US$75 in four rooms, and US$1000 and US$7000 in the remaining two rooms. Conclusions Simple modifications to existing hospital infrastructure considerably increased natural ventilation, and greatly reduced modelled TB transmission risk at little cost.
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Affiliation(s)
- A Roderick Escombe
- Department of Infectious Diseases & Immunity and the Wellcome Trust Centre for Clinical Tropical Medicine, Imperial College London, London, UK
| | - Eduardo Ticona
- Hospital Nacional Dos de Mayo, Lima, Peru.,Universidad Nacional Mayor de San Marcos, Lima, Peru
| | - Víctor Chávez-Pérez
- Hospital Nacional Dos de Mayo, Lima, Peru.,Universidad Nacional Mayor de San Marcos, Lima, Peru
| | - Manuel Espinoza
- Hospital Nacional Dos de Mayo, Lima, Peru.,Universidad Nacional Mayor de San Marcos, Lima, Peru
| | - David A J Moore
- TB Centre, London School of Hygiene and Tropical Medicine, London, UK. .,Universidad Peruana Cayetano Heredia, Lima, Peru.
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Wangari IM, Stone L. Backward bifurcation and hysteresis in models of recurrent tuberculosis. PLoS One 2018; 13:e0194256. [PMID: 29566101 PMCID: PMC5863985 DOI: 10.1371/journal.pone.0194256] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Accepted: 02/27/2018] [Indexed: 11/18/2022] Open
Abstract
An epidemiological model is presented that provides a comprehensive description of the transmission pathways involved for recurrent tuberculosis (TB), whereby cured individuals can become reinfected. Our main goal is to determine conditions that lead to the appearance of a backward bifurcation. This occurs when an asymptotically stable infection free equilibrium concurrently exists with a stable non-trivial equilibria even though the basic reproduction number R0 is less than unity. Although, some 10-30% cases of TB are recurrent, the role of recurrent TB as far as the formation of backward bifurcation is concerned, is rarely if ever studied. The model used here incorporates progressive primary infection, exogenous reinfection, endogenous reactivation and recurrent TB as transmission mechanisms that contribute to TB progression. Unlike other studies of TB dynamics that make use of frequency dependent transmission rates, our analysis provides exact backward bifurcation threshold conditions without resorting to commonly applied approximations and simplifying assumptions. Exploration of the model through analytical and numerical analysis reveal that recurrent TB is sometimes capable of triggering hysteresis effects which allow TB to persist when R0 < 1 even though there is no backward bifurcation. Furthermore, recurrent TB can independently induce backward bifurcation phenomena if it exceeds a certain threshold.
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Affiliation(s)
- Isaac Mwangi Wangari
- School of Science, Department of Mathematics and Geospatial Sciences, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia
- * E-mail:
| | - Lewi Stone
- School of Science, Department of Mathematics and Geospatial Sciences, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia
- Biomathematics Unit, Department of Zoology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
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17
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18
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Mathema B, Andrews JR, Cohen T, Borgdorff MW, Behr M, Glynn JR, Rustomjee R, Silk BJ, Wood R. Drivers of Tuberculosis Transmission. J Infect Dis 2017; 216:S644-S653. [PMID: 29112745 PMCID: PMC5853844 DOI: 10.1093/infdis/jix354] [Citation(s) in RCA: 102] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Measuring tuberculosis transmission is exceedingly difficult, given the remarkable variability in the timing of clinical disease after Mycobacterium tuberculosis infection; incident disease can result from either a recent (ie, weeks to months) or a remote (ie, several years to decades) infection event. Although we cannot identify with certainty the timing and location of tuberculosis transmission for individuals, approaches for estimating the individual probability of recent transmission and for estimating the fraction of tuberculosis cases due to recent transmission in populations have been developed. Data used to estimate the probable burden of recent transmission include tuberculosis case notifications in young children and trends in tuberculin skin test and interferon γ-release assays. More recently, M. tuberculosis whole-genome sequencing has been used to estimate population levels of recent transmission, identify the distribution of specific strains within communities, and decipher chains of transmission among culture-positive tuberculosis cases. The factors that drive the transmission of tuberculosis in communities depend on the burden of prevalent tuberculosis; the ways in which individuals live, work, and interact (eg, congregate settings); and the capacity of healthcare and public health systems to identify and effectively treat individuals with infectious forms of tuberculosis. Here we provide an overview of these factors, describe tools for measurement of ongoing transmission, and highlight knowledge gaps that must be addressed.
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Affiliation(s)
- Barun Mathema
- Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York
| | - Jason R Andrews
- Division of Infectious Diseases and Geographic Medicine, Stanford University, California
| | - Ted Cohen
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut
| | - Martien W Borgdorff
- Centers for Disease Control and Prevention, Kisumu, Kenya
- Department of Clinical Epidemiology, Biostatistics, and Bioinformatics, Academic Medical Center, University of Amsterdam, the Netherlands
| | - Marcel Behr
- McGill International TB Centre, Research Institute of the McGill University Health Centre, Montreal,Canada
| | - Judith R Glynn
- Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, United Kingdom
| | - Roxana Rustomjee
- Tuberculosis Clinical Research Branch, Therapeutics Research Program, Division of AIDS, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, Rockville, Maryland
| | - Benjamin J Silk
- Division of Tuberculosis Elimination, Centers for Disease Control and Prevention, Atlanta, Georgia
| | - Robin Wood
- Desmond Tutu HIV Centre, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, South Africa
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Jabbari A, Castillo-Chavez C, Nazari F, Song B, Kheiri H. A two-strain TB model with multiple latent stages. MATHEMATICAL BIOSCIENCES AND ENGINEERING : MBE 2016; 13:741-785. [PMID: 27775384 DOI: 10.3934/mbe.2016017] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A two-strain tuberculosis (TB) transmission model incorporating antibiotic-generated TB resistant strains and long and variable waiting periods within the latently infected class is introduced. The mathematical analysis is carried out when the waiting periods are modeled via parametrically friendly gamma distributions, a reasonable alternative to the use of exponential distributed waiting periods or to integral equations involving ``arbitrary'' distributions. The model supports a globally-asymptotically stable disease-free equilibrium when the reproduction number is less than one and an endemic equilibriums, shown to be locally asymptotically stable, or l.a.s., whenever the basic reproduction number is greater than one. Conditions for the existence and maintenance of TB resistant strains are discussed. The possibility of exogenous re-infection is added and shown to be capable of supporting multiple equilibria; a situation that increases the challenges faced by public health experts. We show that exogenous re-infection may help established resilient communities of actively-TB infected individuals that cannot be eliminated using approaches based exclusively on the ability to bring the control reproductive number just below 1.
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Affiliation(s)
- Azizeh Jabbari
- Department of Applied Mathematics, Faculty of Mathematical Sciences, University of Tabriz, Tabriz, Iran.
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20
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Developing vaccines to prevent sustained infection with Mycobacterium tuberculosis : Conference proceedings. Vaccine 2015; 33:3056-64. [DOI: 10.1016/j.vaccine.2015.03.061] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Revised: 03/10/2015] [Accepted: 03/18/2015] [Indexed: 01/08/2023]
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21
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Orme IM, Basaraba RJ. The formation of the granuloma in tuberculosis infection. Semin Immunol 2014; 26:601-9. [DOI: 10.1016/j.smim.2014.09.009] [Citation(s) in RCA: 101] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Revised: 09/11/2014] [Accepted: 09/15/2014] [Indexed: 12/13/2022]
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25
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Global Dynamics of a Tuberculosis Epidemic Model and the Influence of Backward Bifurcation. ACTA ACUST UNITED AC 2012. [DOI: 10.1007/s10852-012-9210-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Affiliation(s)
- Salmaan Keshavjee
- Program in Infectious Disease and Social Change, Department of Global Health and Social Medicine, Harvard Medical School, Boston, MA 02115, USA.
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Gomes MGM, Aguas R, Lopes JS, Nunes MC, Rebelo C, Rodrigues P, Struchiner CJ. How host heterogeneity governs tuberculosis reinfection? Proc Biol Sci 2012; 279:2473-8. [PMID: 22357260 DOI: 10.1098/rspb.2011.2712] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Recurrent episodes of tuberculosis (TB) can be due to relapse of latent infection or exogenous reinfection, and discrimination is crucial for control planning. Molecular genotyping of Mycobacterium tuberculosis isolates offers concrete opportunities to measure the relative contribution of reinfection in recurrent disease. Here, a mathematical model of TB transmission is fitted to data from 14 molecular epidemiology studies, enabling the estimation of relevant epidemiological parameters. Meta-analysis reveals that rates of reinfection after successful treatment are higher than rates of new TB, raising an important question about the underlying mechanism. We formulate two alternative mechanisms within our model framework: (i) infection increases susceptibility to reinfection or (ii) infection affects individuals differentially, thereby recruiting high-risk individuals to the group at risk for reinfection. The second mechanism is better supported by the fittings to the data, suggesting that reinfection rates are inflated through a population phenomenon that occurs in the presence of heterogeneity in individual risk of infection. As a result, rates of reinfection are higher when measured at the population level even though they might be lower at the individual level. Finally, differential host recruitment is modulated by transmission intensity, being less pronounced when incidence is high.
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Affiliation(s)
- M Gabriela M Gomes
- Instituto Gulbenkian de Ciência, Apartado 14, 2781-901 Oeiras, Portugal.
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Ford C, Yusim K, Ioerger T, Feng S, Chase M, Greene M, Korber B, Fortune S. Mycobacterium tuberculosis--heterogeneity revealed through whole genome sequencing. Tuberculosis (Edinb) 2012; 92:194-201. [PMID: 22218163 DOI: 10.1016/j.tube.2011.11.003] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2011] [Accepted: 11/07/2011] [Indexed: 11/24/2022]
Abstract
The emergence of whole genome sequencing (WGS) technologies as primary research tools has allowed for the detection of genetic diversity in Mycobacterium tuberculosis (Mtb) with unprecedented resolution. WGS has been used to address a broad range of topics, including the dynamics of evolution, transmission and treatment. Here, we have analyzed 55 publically available genomes to reconstruct the phylogeny of Mtb, and we have addressed complications that arise during the analysis of publically available WGS data. Additionally, we have reviewed the application of WGS to the study of Mtb and discuss those areas still to be addressed, moving from global (phylogeography), to local (transmission chains and circulating strain diversity), to the single patient (clonal heterogeneity) and to the bacterium itself (evolutionary studies). Finally, we discuss the current WGS approaches, their strengths and limitations.
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Affiliation(s)
- Chris Ford
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, 665 Huntington Avenue, Building 1, Boston, MA 02115, USA
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MOGHADAS SM, ALEXANDER ME. EXOGENOUS REINFECTION AND RESURGENCE OF TUBERCULOSIS: A THEORETICAL FRAMEWORK. J BIOL SYST 2011. [DOI: 10.1142/s0218339004001063] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The importance of exogenous reinfection versus endogenous reactivation for the resurgence of tuberculosis (TB) has been a matter of ongoing debate. Previous mathematical models of TB give conflicting results on the possibility of multiple stable equilibria in the presence of reinfection, and hence the failure to control the disease even when the basic reproductive number is less than unity. The present study reconsiders the effect of exogenous reinfection, by extending previous studies to incorporate a generalized rate of reinfection as a function of the number of actively infected individuals. A mathematical model is developed to include all possible routes to the development of active TB (progressive primary infection, endogenous reactivation, and exogenous reinfection). The model is qualitatively analyzed to show the existence of multiple equilibria under realistic assumptions and plausible range of parameter values. Two examples, of unbounded and saturated incidence rates of reinfection, are given, and simulation results using estimated parameter values are presented. The results reflect exogenous reinfection as a major cause of TB emergence, especially in high prevalence areas, with important public health implications for controlling its spread.
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Affiliation(s)
- S. M. MOGHADAS
- Institute for Biodiagnostics, National Research Council Canada, Winnipeg, Manitoba, R3B 1Y6, Canada
| | - M. E. ALEXANDER
- Institute for Biodiagnostics, National Research Council Canada, Winnipeg, Manitoba, R3B 1Y6, Canada
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Shabbeer A, Ozcaglar C, Yener B, Bennett KP. Web tools for molecular epidemiology of tuberculosis. INFECTION GENETICS AND EVOLUTION 2011; 12:767-81. [PMID: 21903179 DOI: 10.1016/j.meegid.2011.08.019] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Revised: 08/14/2011] [Accepted: 08/19/2011] [Indexed: 01/03/2023]
Abstract
In this study we explore publicly available web tools designed to use molecular epidemiological data to extract information that can be employed for the effective tracking and control of tuberculosis (TB). The application of molecular methods for the epidemiology of TB complement traditional approaches used in public health. DNA fingerprinting methods are now routinely employed in TB surveillance programs and are primarily used to detect recent transmissions and in outbreak investigations. Here we present web tools that facilitate systematic analysis of Mycobacterium tuberculosis complex (MTBC) genotype information and provide a view of the genetic diversity in the MTBC population. These tools help answer questions about the characteristics of MTBC strains, such as their pathogenicity, virulence, immunogenicity, transmissibility, drug-resistance profiles and host-pathogen associativity. They provide an integrated platform for researchers to use molecular epidemiological data to address current challenges in the understanding of TB dynamics and the characteristics of MTBC.
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Affiliation(s)
- Amina Shabbeer
- Department of Mathematical Science, Rensselaer Polytechnic Institute, Troy, NY 12180, USA.
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Wang JY, Hsu HL, Yu MC, Chiang CY, Yu FL, Yu CJ, Lee LN, Yang PC. Mixed infection with Beijing and non-Beijing strains in pulmonary tuberculosis in Taiwan: prevalence, risk factors, and dominant strain. Clin Microbiol Infect 2010; 17:1239-45. [PMID: 20946415 DOI: 10.1111/j.1469-0691.2010.03401.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Patients with pulmonary tuberculosis (TB) can be simultaneously infected with different strains of Mycobacterium tuberculosis (mixed infection). We investigated the prevalence and risk factors of mixed infection by Beijing and non-Beijing strains in pulmonary TB patients in Taiwan. We developed a quantitative PCR method to simultaneously detect the presence of Beijing and non-Beijing strains. A total of 868 pretreatment samples (from 868 patients), including 563 sputum samples smear-positive for acid-fast bacilli and 305 liquid medium samples culture-positive for mycobacteria, were tested. Medical records of patients with culture-confirmed pulmonary TB were reviewed. The detection limit of our quantitative PCR method was five copies of target sequences. With mycobacterial culture result as the reference standard, the sensitivity and specificity of our quantitative PCR method were 95% and 98%, respectively. M. tuberculosis strains were isolated in 466 samples, of which 231 (49.6%) were infected with a Beijing strain. Another 14 patients (3.0%) had mixed infection, with the Beijing strain being the dominant strain in 13 (93%). Age <25 years with pulmonary cavities was associated with mixed infection. In patients infected with non-Beijing strains, the bacterial load of non-Beijing strains was lower among those with mixed infection than among those without. Our quantitative PCR method was accurate in detecting Beijing and non-Beijing strains in smear-positive sputum and culture-positive liquid medium samples. Mixed infection was present in pulmonary TB patients (3.0%), especially in those aged <25 years with pulmonary cavities. Beijing strains seem to be more dominant than non-Beijing strains in patients with mixed infection.
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Affiliation(s)
- J-Y Wang
- Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
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Yang HM, Raimundo SM. Assessing the effects of multiple infections and long latency in the dynamics of tuberculosis. Theor Biol Med Model 2010; 7:41. [PMID: 21059256 PMCID: PMC2995482 DOI: 10.1186/1742-4682-7-41] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Accepted: 11/08/2010] [Indexed: 11/10/2022] Open
Abstract
In order to achieve a better understanding of multiple infections and long latency in the dynamics of Mycobacterium tuberculosis infection, we analyze a simple model. Since backward bifurcation is well documented in the literature with respect to the model we are considering, our aim is to illustrate this behavior in terms of the range of variations of the model's parameters. We show that backward bifurcation disappears (and forward bifurcation occurs) if: (a) the latent period is shortened below a critical value; and (b) the rates of super-infection and re-infection are decreased. This result shows that among immunosuppressed individuals, super-infection and/or changes in the latent period could act to facilitate the onset of tuberculosis. When we decrease the incubation period below the critical value, we obtain the curve of the incidence of tuberculosis following forward bifurcation; however, this curve envelops that obtained from the backward bifurcation diagram.
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Affiliation(s)
- Hyun M Yang
- UNICAMP-IMECC, Departamento de Matemática Aplicada, Praça Sérgio Buarque de Holanda, 651, CEP: 13083-859, Campinas, SP, Brazil.
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Reply. AJR Am J Roentgenol 2009. [DOI: 10.2214/ajr.08.1896] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Cardona PJ. A dynamic reinfection hypothesis of latent tuberculosis infection. Infection 2009; 37:80-6. [PMID: 19308318 DOI: 10.1007/s15010-008-8087-y] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2008] [Accepted: 09/10/2008] [Indexed: 12/19/2022]
Abstract
BACKGROUND It has been traditionally postulated that individuals, once infected by Mycobacterium tuberculosis, will retain throughout their entire lifetime latent bacilli which will remain dormant in old lesions. This bacillus would then be the source of a later reactivation of active tuberculosis (TB), with the aid of resuscitation factors. Unfortunately, the presence of these bacilli can only be predicted by indirect immunological methods, such as the tuberculin skin test (TST) or T cell interferon-gamma release assays. Other evidence shows that a 9-month isoniazid treatment of TST+ individuals converting to TB reduces the incidence of TB by approximately 90%. QUESTIONS Taking into account this widely accepted framework, I suggest that there are at least three relevant questions to answer: (1) How can dormant bacilli remain in the lungs for an entire lifetime, taking into account constant cellular turnover and the healing of damaged tissues? (2) What provides the resuscitation factor to dormant bacilli, assuming that these latent bacilli are indeed present inside old lesions? (3) Why can a 9-month treatment with isoniazid eliminate dormant bacilli? As isoniazid is active only against growing bacilli, and thus is only able to destroy them after reactivation of latent bacilli, this treatment should have to be provided for life if the traditionally accepted postulate is correct. HYPOTHESIS For a better understanding of latent TB infection. I propose a hypothesis that describes a dynamic scenario of constant endogenous reinfection with M. tuberculosis which explains the efficacy of the current standard of treatment. If this hypothesis is true, new strategies for the management of TB may arise.
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Affiliation(s)
- P-J Cardona
- Dept. of Microbiology, Germans Trias I Pujol Health Science Research Institute Foundation, Autonomous University of Barcelona, Badalona, Catalonia, Spain.
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Zhou Y, Khan K, Feng Z, Wu J. Projection of tuberculosis incidence with increasing immigration trends. J Theor Biol 2008; 254:215-28. [DOI: 10.1016/j.jtbi.2008.05.026] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2007] [Revised: 05/17/2008] [Accepted: 05/19/2008] [Indexed: 11/17/2022]
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Farnia P, Masjedi MR, Varahram M, Mirsaeidi M, Ahmadi M, Khazampour M, Tabarsi P, Baghei P, Marjane M, Bahadori M, Zarifi AZ, Velayati AA. The recent-transmission of Mycobacterium tuberculosis strains among Iranian and Afghan relapse cases: a DNA-fingerprinting using RFLP and spoligotyping. BMC Infect Dis 2008; 8:109. [PMID: 18681980 PMCID: PMC2518555 DOI: 10.1186/1471-2334-8-109] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2007] [Accepted: 08/06/2008] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Relapse of tuberculosis (TB) may develop as the result of reactivation of the endogenous primary infection, or as a result of a exogenous reinfection. This survey evaluated the rate of reactivation versus recent transmission among Iranian and Afghan relapse cases. METHODS The sputum specimens were digested, examined microscopically for acid-fast bacilli, and inoculated into Löwenstein-Jensen slants by standard procedures. Thereafter, the susceptibility and identification tests were performed on culture positive specimens. Subsequently, the strains that were identified as Mycobacterium tuberculosis (258 isolates) were subjected to IS6110 restriction fragment length polymorphism (RFLP) and spoligotyping. Additional patient's information was collected for further epidemiological analysis. Patients whose isolates had identical genotyping patterns were considered a cluster with recent transmission episode. RESULTS Out of 258 available isolates, 72(28%) had multi-drug resistant (MDR-TB) in ratio and 42 (16.2%) had other resistant. Notably, 38 of MDR-TB cases (52%) were isolated from Afghan patients. By IS6110-RFLP typing method, 65 patients (25%) were clustered in 29 clusters. In cluster cases, the intra-community transmissions between Iranian and Afghan patients were 41%. All MDR-TB patients in clusters had either Haarlem I or Beijing characteristic. The risk factors like sex, family history, close contact, living condition, PPD test result and site of TB infection were not associated with clustering. Although, the MDR-TB strains were more frequent in non-cluster cases (31%) than cluster one(18%) (P < 0.05). Majority of M. tuberculosis strains isolated from non-cluster cases were belong to EAI3 (51; 30%) and CASI(32;18.6%) superfamilies. CONCLUSION During the studied period, reactivation of a previous infection remain the more probable cause of recurrence. Although, the evidence of intra- community transmission between Iranian and Afghan TB cases, highlighted the impact of afghan immigrants in national tuberculosis control program (NTP) of Iran.
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Affiliation(s)
- Parissa Farnia
- Mycobacteriology Research Centre, Iranian National Reference TB Laboratory, National Research Institute Of Tuberculosis and Lung Disease, Shaheed Bahesti University of Medical Sciences (Medical Campus), Darabad, Tehran, Iran.
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Smith KC, Orme IM, Starke JR. Tuberculosis vaccines. Vaccines (Basel) 2008. [DOI: 10.1016/b978-1-4160-3611-1.50037-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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Keshavjee S, Gelmanova IY, Pasechnikov AD, Mishustin SP, Andreev YG, Yedilbayev A, Furin JJ, Mukherjee JS, Rich ML, Nardell EA, Farmer PE, Kim JY, Shin SS. Treating multidrug-resistant tuberculosis in Tomsk, Russia: developing programs that address the linkage between poverty and disease. Ann N Y Acad Sci 2007; 1136:1-11. [PMID: 17954675 DOI: 10.1196/annals.1425.009] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Tuberculosis (TB) and multidrug-resistant TB (MDR-TB) are diseases of poverty. Because Mycobacterium tuberculosis exists predominantly in a social space often defined by poverty and its comorbidities--overcrowded or congregate living conditions, substance dependence or abuse, and lack of access to proper health services, to name a few--the biology of this organism and of TB drug resistance is intimately linked to the social world in which patients live. This association is demonstrated in Russia, where political changes in the 1990s resulted in increased socioeconomic inequality and a breakdown in health services. The effect on TB and MDR-TB is reflected both in terms of a rise in TB and MDR-TB incidence and increased morbidity and mortality associated with the disease. We present the case example of Tomsk Oblast to delineate how poverty contributed to a growing MDR-TB epidemic and increasing socioeconomic barriers to successful care, even when available. The MDR-TB pilot project implemented in Tomsk addressed both programmatic and socioeconomic factors associated with unfavorable outcomes. The result has been a strengthening of the overall TB control program in the region and improved case-holding for the most vulnerable patients. The model of MDR-TB care in Tomsk is applicable for other resource-poor settings facing challenges to TB and MDR-TB control.
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Affiliation(s)
- S Keshavjee
- Division of Social Medicine and Health Inequalities, Brigham and Women's Hospital, FXB Bldg.-7th floor, 651 Huntington Ave., Boston, MA 02115, USA.
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Acha J, Sweetland A, Guerra D, Chalco K, Castillo H, Palacios E. Psychosocial support groups for patients with multidrug-resistant tuberculosis: Five years of experience. Glob Public Health 2007; 2:404-17. [DOI: 10.1080/17441690701191610] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Cohen T, Colijn C, Finklea B, Murray M. Exogenous re-infection and the dynamics of tuberculosis epidemics: local effects in a network model of transmission. J R Soc Interface 2007; 4:523-31. [PMID: 17251134 PMCID: PMC2373405 DOI: 10.1098/rsif.2006.0193] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Infection with Mycobacterium tuberculosis leads to tuberculosis (TB) disease by one of the three possible routes: primary progression after a recent infection; re-activation of a latent infection; or exogenous re-infection of a previously infected individual. Recent studies show that optimal TB control strategies may vary depending on the predominant route to disease in a specific population. It is therefore important for public health policy makers to understand the relative frequency of each type of TB within specific epidemiological scenarios. Although molecular epidemiologic tools have been used to estimate the relative contribution of recent transmission and re-activation to the burden of TB disease, it is not possible to use these techniques to distinguish between primary disease and re-infection on a population level. Current estimates of the contribution of re-infection therefore rely on mathematical models which identify the parameters most consistent with epidemiological data; these studies find that exogenous re-infection is important only when TB incidence is high. A basic assumption of these models is that people in a population are all equally likely to come into contact with an infectious case. However, theoretical studies demonstrate that the social and spatial structure can strongly influence the dynamics of infectious disease transmission. Here, we use a network model of TB transmission to evaluate the impact of non-homogeneous mixing on the relative contribution of re-infection over realistic epidemic trajectories. In contrast to the findings of previous models, our results suggest that re-infection may be important in communities where the average disease incidence is moderate or low as the force of infection can be unevenly distributed in the population. These results have important implications for the development of TB control strategies.
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Affiliation(s)
- Ted Cohen
- Division of Social Medicine and Health Inequalities, Brigham and Women's Hospital, One Brigham Circle, Boston, MA 02120, USA
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42
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Gao N, Niu J. Modeling particle dispersion and deposition in indoor environments. ATMOSPHERIC ENVIRONMENT (OXFORD, ENGLAND : 1994) 2007; 41:3862-3876. [PMID: 32362759 PMCID: PMC7185799 DOI: 10.1016/j.atmosenv.2007.01.016] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2006] [Revised: 11/10/2006] [Accepted: 01/03/2007] [Indexed: 05/19/2023]
Abstract
Particle dispersion and deposition in man-made enclosed environments are closely related to the well-being of occupants. The present study developed a three-dimensional drift-flux model for particle movements in turbulent indoor airflows, and combined it into Eulerian approaches. To account for the process of particle deposition at solid boundaries, a semi-empirical deposition model was adopted in which the size-dependent deposition characteristics were well resolved. After validation against the experimental data in a scaled isothermal chamber and in a full-scale non-isothermal environmental chamber, the drift-flux model was used to investigate the deposition rates and human exposures to particles from two different sources with three typical ventilation systems: mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD). For particles originating from the supply air, a V-shaped curve of the deposition velocity variation as a function of particle size was observed. The minimum deposition appeared at 0.1- 0.5 μ m . For supermicron particles, the ventilation type and air exchange rate had an ignorable effect on the deposition rate. The movements of submicron particles were like tracer gases while the gravitational settling effect should be taken into account for particles larger than 2.5 μ m . The temporal increment of human exposure to a step-up particle release in the supply air was determined, among many factors, by the distance between the occupant and air outlet. The larger the particle size, the lower the human exposure. For particles released from an internal heat source, the concentration stratification of small particles (diameter < 10 μ m ) in the vertical direction appeared with DV and UFAD, and it was found the advantageous principle for gaseous pollutants that a relatively less-polluted occupied zone existed in DV and UFAD was also applicable to small particles.
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Shamputa IC, Van Deun A, Salim MAH, Hossain MA, Fissette K, de Rijk P, Rigouts L, Portaels F. Endogenous reactivation and true treatment failure as causes of recurrent tuberculosis in a high incidence setting with a low HIV infection. Trop Med Int Health 2007; 12:700-8. [PMID: 17550467 DOI: 10.1111/j.1365-3156.2007.01840.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
OBJECTIVE To determine the relative frequencies of reinfection vs. reactivation or treatment failure in patients from a high tuberculosis incidence setting with a low prevalence of HIV infection. METHOD We performed DNA fingerprinting on serial isolates from one and multiple TB episodes from 97 retreatment patients; 35 patients had been previously cured, whereas 62 had not. RESULTS DNA fingerprinting patterns of recurrence Mycobacterium tuberculosis isolates of 5 of the 35 previously cured patients did not match with those of the corresponding initial isolates, indicating reinfection. We did not document reinfection during treatment. Isolates from each of the remaining 30 previously cured patients had identical DNA fingerprinting results, indicating reactivation. DNA fingerprinting patterns of isolates from the 62 patients with persistently positive sputum smears were identical, suggesting treatment failure. CONCLUSION These findings suggest that reinfection is not a common cause of relapse and treatment failure in this rural predominantly HIV-free population despite the high incidence of TB.
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Affiliation(s)
- Isdore Chola Shamputa
- Prince Leopold Institute of Tropical Medicine, Mycobacteriology Unit, Antwerp, Belgium.
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Chao CYH, Wan MP. A study of the dispersion of expiratory aerosols in unidirectional downward and ceiling-return type airflows using a multiphase approach. INDOOR AIR 2006; 16:296-312. [PMID: 16842610 DOI: 10.1111/j.1600-0668.2006.00426.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Dispersion characteristics of expiratory aerosols were investigated in an enclosure with two different idealized airflow patterns: the ceiling-return and the unidirectional downward. A multiphase numerical model, which was able to capture the polydispersity and evaporation features of the aerosols, was adopted. Experiments employing optical techniques were conducted in a chamber with downward airflow pattern to measure the dispersion of aerosols. Some of the numerical results were compared with the chamber measurement results. Reasonable agreement was found. Small aerosols (initial size <or=45 microm) had settling times of below 20 s in downward flow but increased to 32-80 s in ceiling-return flow. Lateral dispersion was limited to around 0.3 m in downward flow, in which only turbulent dispersion was significant. It increased to over 2 m in ceiling-return flow, which had a combination of both turbulant dispersion and bulk flow transport mechanisms. The significance of aerosol transport by bulk flow was about an order of magnitude stronger than that by turbulent dispersion. However, results also show that aerosols could be dispersed for considerable distances solely by turbulence if they were suspended longer. Large aerosols settled within very short time due to heavy gravitational effects. The results provided new insights in designing proper bed spacing in hospital ward environments. This study shows that transport by bulk airflow stream was the major dispersion mechanism of expiratory aerosols in ventilated indoor environments. Dispersion by turbulence was about an order of magnitude less than that by bulk flow transport but considerable distance could be achieved by turbulent dispersion with long enough settling time. It was demonstrated that the dispersion of expiratory aerosol could be controlled by manipulating the ventilation airflow patterns in indoor environments.
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Affiliation(s)
- C Y H Chao
- Department of Mechanical Engineering, The Hong Kong University of Science and Technology, Hong Kong, China.
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Helke KL, Mankowski JL, Manabe YC. Animal models of cavitation in pulmonary tuberculosis. Tuberculosis (Edinb) 2005; 86:337-48. [PMID: 16359922 DOI: 10.1016/j.tube.2005.09.001] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2005] [Indexed: 11/24/2022]
Abstract
Transmission of tuberculosis occurs with the highest frequency from patients with extensive, cavitary, pulmonary disease and positive sputum smear microscopy. In animal models of tuberculosis, the development of caseous necrosis is an important prerequisite for the formation of cavities although the immunological triggers for liquefaction are unknown. We review the relative merits and the information gleaned from the available animal models of pulmonary cavitation. Understanding the host-pathogen interaction important to the formation of cavities may lead to new strategies to prevent cavitation and thereby, block transmission.
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Affiliation(s)
- Kris L Helke
- Department of Comparative Medicine, Johns Hopkins University School of Medicine, 733 N. Broadway, Room 811, Baltimore, MD 21205, USA
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García-Pachón E, Rodríguez J. Epidemiología molecular de la tuberculosis: principales hallazgos y su aplicación en España. Arch Bronconeumol 2005. [DOI: 10.1157/13081251] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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García-Pachón E, Rodríguez JC. Molecular Epidemiology of Tuberculosis: Main Findings and Their Application in Spain. ACTA ACUST UNITED AC 2005; 41:618-24. [PMID: 16324601 DOI: 10.1016/s1579-2129(06)60296-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- E García-Pachón
- Sección de Neumología, Hospital General Universitario, Elche, Alicante, Spain.
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Abstract
It was Robert Koch who recognized the spectrum of pathology of tuberculosis (TB) in different animal species. The examination of clinical specimens from infected humans and animals confirmed the variable patterns of pathological reactions in different species. Guinea pigs are innately susceptible while humans, mice and rabbits show different level of resistance depending upon their genotype. The studies of TB in laboratory animals such as mice, rabbits and guinea pigs have significantly increased our understanding of the aetiology, virulence and pathogenesis of the disease. The introduction of less than five virulent organisms into guinea pigs by the respiratory route can produce lung lesions, bacteraemia and fatal diseases, which helped the extrapolation of results of such experiments to humans. The similarities in the course of clinical infection between guinea pigs and humans allow us to model different forms of TB and to evaluate the protective efficacy of candidate vaccines in such systems. The only limitation of this model, however, is a dearth of immunological reagents that are required for the qualitative and quantitative evaluation of the immune responses, with special reference to cytokines and cell phenotypes. Another limitation is the higher cost of guinea pigs compared with mice. The rabbit is relatively resistant to Mycobacterium tuberculosis, however following infection with virulent Mycobacterium bovis, the rabbit produces pulmonary cavities like humans. The rabbit model, however, is also limited by the lack of the immunological reagents. Mice are the animal of choice for studying the immunology of mycobacterial infections and have contributed much to our current understanding of the roles of various immunological mechanisms of resistance. The resistance of mice to the development of classic TB disease, however, represents a significant disadvantage of the mouse model. Although non-human primates are closely related to humans, owing to high cost and handing difficulties they have not been exploited to a large extent. As all existing animal models fail to mimic the human disease perfectly, efforts should be focused on the development of the non-human primate(s) as the alternative animal model for TB.
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Affiliation(s)
- U D Gupta
- Central JALMA Institute for Leprosy & other Mycobacterial Disease (ICMR), Tajganj, Agra 282001, India.
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de Vries G, van Hest RA. From contact investigation to tuberculosis screening of drug addicts and homeless persons in Rotterdam. Eur J Public Health 2005; 16:133-6. [PMID: 16230316 DOI: 10.1093/eurpub/cki203] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND In early 2001 there were indications that tuberculosis (TB) was increasingly becoming a problem among drug addicts and homeless persons in Rotterdam, after a periodical screening was discontinued in 1997. A contact investigation around a homeless drug addicted man in Rotterdam with infectious pulmonary TB is described. Contact investigation: A total of 507 drug addicts, homeless persons, and staff of facilities for these risk groups were examined with tuberculin skin testing (TST) and chest radiography. DNA fingerprinting of mycobacteriological cultures through Restricted Fragment Length Polymorphism methodology and molecular epidemiology investigation through cluster analysis were performed. OUTCOME TST showed an infection prevalence of 29%, especially among staff of services for drug addicts and homeless persons. Six persons with active intrathoracic TB were identified. Cluster analysis demonstrated no relation with the initial case but showed intense transmission of TB among drug addicts and homeless persons in Rotterdam by multiple sources. As a consequence of the findings, a proposal to the Council of the City of Rotterdam resulted in the re-introduction of a comprehensive TB screening programme among these risk groups with mobile digital X-ray units (MXUs). CONCLUSION This contact investigation gradually obtained the characteristics of a screening of drug addicts and homeless persons. Novel technologies, such as MXUs, facilitate appropriate and efficient outreach approaches to TB control among difficult-to-reach groups. This method and knowledge of individual fingerprints and clusters of TB patients are indispensable for underpinning proposals for change of local TB control strategies and convincing local authorities of the rationale.
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Affiliation(s)
- Gerard de Vries
- Department of Tuberculosis Control, Municipal Health Service Rotterdam, PO Box 70032, 3000 LP Rotterdam, The Netherlands.
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Abstract
Whether the development of active tuberculosis in people with previous tuberculous infection represents an episode of endogenous reactivation or exogenous reinfection has been debated for decades. Articles proposing the unitary concept of pathogenesis of tuberculosis in the 1960s initiated a period in which reinfection was considered to be an uncommon cause of tuberculosis. To review evidence demonstrating the occurrence of tuberculosis due to exogenous reinfection, we did a literature search covering publications from 1966 until the present, and found that there was substantial evidence--both experimental and epidemiological--supporting the role of exogenous reinfection in tuberculosis. However, only models based on estimates of the annual risk of infection and the incidence of tuberculosis provided a quantitative estimate of the relative contribution of exogenous reinfection to the burden of tuberculosis. Better estimates of the contribution of exogenous reinfection to new cases of tuberculosis may need to be considered in tuberculosis control strategies.
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Affiliation(s)
- Chen-Yuan Chiang
- Department of Scientific Activities, International Union Against Tuberculosis and Lung Disease, Paris, France.
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