Recurrent tuberculosis risk among HIV-infected adults in Tanzania with prior active tuberculosis

Loss to follow-up among people living with HIV on tuberculosis preventive treatment at four regional referral hospitals, Uganda, 2019-2021

Introduction

Tuberculosis (TB) remains the leading cause of death among people living with HIV (PLHIV). TB preventive treatment (TPT) can prevent active TB infection in PLHIV for several years after it is completed. During 2019-2021, the six-month course of TPT (using isoniazid) was the most readily available in Uganda; however, program data indicated a TPT program loss to follow-up (LTFU) rate of 12 % during this period. We evaluated factors associated with TPT LTFU among PLHIV in four regional referral hospitals (RRHs) in Uganda from 2019 to 2021.

Methods

We abstracted program data from TPT registers on patient LTFU at Masaka, Mbale, Mubende, and Jinja RRHs. Additional data collected included client demographics, duration on HIV antiretroviral therapy (ART), year of TPT initiation, adherence, and point of entry. LTFU was defined as the failure to finish six consecutive months of isoniazid without stopping for more than two months at a time. We conducted bivariate analysis using the chi-square test for independence. Variables with p < 0.05 in bivariate analysis were included in a logistic regression model to establish independent factors associated with LTFU.

Results

Overall, 24,206 clients were started on TPT in the four RRHs. Their median age was 40 years (range, 1-90 years), and 15,962 (66 %) were female. A total of 22,260 (92 %) had TPT adherence >95 %. Independent factors associated with LTFU included being on ART for <3 months (AOR: 3.1, 95 % CI: 2.1-4.5) and 20-24 years (AOR: 4.7, 95 % CI: 1.9-12) or 25-29 years (AOR: 3.3, 95 % CI: 1.3-8.2) compared to 15-19 years.

Conclusions

PLHIV just starting ART and young adults had higher odds of being LTFU from TPT during 2019-2021 in the four RRHs. Close follow-up of PLHIV aged 20-29 years and those newly initiated on ART could improve TPT completion.

Efficacy, safety, and tolerability of isoniazid preventive therapy for tuberculosis in people living with HIV

OBJECTIVE

The aim of this study was to systematically assess the efficacy, safety, and tolerability of isoniazid preventive therapy (IPT) for tuberculosis (TB) in people with HIV (PWH).

DESIGN

A systematic review and meta-analysis.

METHODS

A thorough literature search was performed using PubMed, Cochrane CENTRAL, and Google Scholar from their inception to June 30, 2021. All randomized controlled trials (RCTs) investigating the efficacy, safety, or tolerability of IPT on PWH compared with placebo or active comparators were included in the study. The heterogeneity among the studies was identified by using the I2 statistic and Cochran's Q test.

RESULTS

Out of the 924 nonduplicate RCTs identified through database searching and other sources, 26 studies comprising 38 005 patients were included. The overall effect estimate identified the reduction of active TB incidence [odds ratio (OR) 0.69; 95% confidence interval (95% CI) 0.57-0.84; P  < 0.001], but not all-cause mortality (OR 0.91; 95% CI 0.82, 1.02; P  = 0.10) with IPT compared with the control. In addition, no significant association was identified between the use of IPT and the risk of peripheral neuropathy (OR 1.50; 95% CI 0.96-2.36; P  = 0.08) and hepatotoxicity (OR 1.21; 95% CI 0.97-1.52; P  = 0.09).

CONCLUSION

This systematic review and meta-analysis identified a significant reduction in the incidence of active TB, but not all-cause mortality, among PWH who received IPT compared with the control. Lesser number of outcomes may be the reason for nonsignificant results in terms of safety outcomes of IPT. Therefore, there is a need for extensive and long-term studies to address these issues further, especially in TB/HIV endemic areas.

Evaluation of the uptake of tuberculosis preventative therapy for people living with HIV in Namibia: a multiple methods analysis

Background

In 2016, Namibia had ~ 230,000 people living with HIV (PLHIV) and 9154 new tuberculosis (TB) cases, including 3410 (38%) co-infected cases. TB preventative therapy (TPT), consisting of intensive case finding and isoniazid preventative therapy, is critical to reducing TB disease and mortality.

Methods

Between November 2014 and February 2015, data was abstracted from charts of PLHIV enrolled in HIV treatment. Fifty-five facilities were purposively selected based on patient volume, type and location. Charts were randomly sampled. The primary outcome was to estimate baseline TPT in PLHIV, using nationally weighted proportions. Qualitative surveys were conducted and summarized to evaluate TPT practices and quantify challenges encountered by health care workers (HCW).

Results

Among 861 PLHIV sampled, 96% were eligible for TPT services, of which 87.1% were screened for TB at least once. For PLHIV eligible for preventative therapy (646/810; 82.6%), 45.4% (294/646) initiated therapy and 45.7% (139/294) of those completed therapy. The proportion of eligible PLHIV completing TB screening, initiating preventative therapy and then completing preventative therapy was 20.7%. Qualitative surveys with 271 HCW identified barriers to TPT implementation including: lack of training (61.3% reported receiving training on TPT); misunderstandings about timing of TPT initiation (46.7% correctly reported TPT should be started with antiretroviral therapy); and variable screening practices and responsibilities (66.1% of HCWs screened for TB at every encounter). Though barriers were evident, 72.2% HCWs surveyed described their clinical performance as very good, often placing responsibility of difficulties on patients and downplaying challenges like staff shortages and medication stock outs.

Conclusions

In this study, only 1 in 5 eligible PLHIV completed the TPT cascade in Namibia. Lack of training, irregularities with TB screening and timing of TPT, unclear prescribing and recording responsibilities, and a clinical misperception may have contributed to suboptimal programmatic implementation. Addressing these challenges will be critical with continued TPT scale-up.

Mycobacterium Tuberculosis and Interactions with the Host Immune System: Opportunities for Nanoparticle Based Immunotherapeutics and Vaccines

Tuberculosis (TB) caused by Mycobacterium tuberculosis remains a deadly infectious disease. The thin pipeline of new drugs for TB, the ineffectiveness in adults of the only vaccine available, i.e. the Bacillus Calmette-Guerin vaccine, and increasing global antimicrobial resistance, has reinvigorated interest in immunotherapies. Nanoparticles (NPs) potentiate the effect of immune modulating compounds (IMC), enabling cell targeting, improved transfection of antigens, enhanced compound stability and provide opportunities for synergistic action, via delivery of multiple IMCs. In this review we describe work performed in the application of NPs towards achieving immune modulation for TB treatment and vaccination. Firstly, we present a comprehensive review of M. tuberculosis and how the bacterium modulates the host immune system. We find that current work suggest great promise of NP based immunotherapeutics as novel treatments and vaccination systems. There is need to intensify research efforts in this field, and rationally design novel NP immunotherapeutics based on current knowledge of the mycobacteriology and immune escape mechanisms employed by M. tuberculosis.

Challenges Across the HIV Care Continuum for Patients With HIV/TB Co-infection in Atlanta, GA [corrected]

Background

Antiretroviral therapy (ART) for persons with HIV infection prevents tuberculosis (TB) disease. Additionally, sequential ART after initiation of TB treatment improves outcomes. We examined ART use, retention in care, and viral suppression (VS) before, during, and 3 years following TB treatment for an inner-city cohort in the United States.

Methods

Retrospective cohort study among persons treated for culture-confirmed TB between 2008 and 2015 at an inner-city hospital.

Results

Among 274 persons with culture-confirmed TB, 96 (35%) had HIV co-infection, including 23 (24%) new HIV diagnoses and 73 (76%) previous diagnoses. Among those with known HIV prior to TB, the median time of known HIV was 6 years, and only 10 (14%) were on ART at the time of TB diagnosis. The median CD4 at TB diagnosis was 87 cells/uL. Seventy-four (81%) patients received ART during treatment for TB, and 47 (52%) has VS at the end of TB treatment. Only 32% of patients had continuous VS 3 years after completing TB treatment. There were 3 TB recurrences and 3 deaths post–TB treatment; none of these patients had retention or VS after TB treatment.

Conclusions

Among persons with active TB co-infected with HIV, we found that the majority had known HIV and were not on ART prior to TB diagnosis, and retention in care and VS post–TB treatment were very low. Strengthening the HIV care continuum is needed to improve HIV outcomes and further reduce rates of active TB/HIV co-infection in our and similar settings.

Integrating tuberculosis screening in Kenyan Prevention of Mother-To-Child Transmission programs

BACKGROUND

Tuberculosis (TB) screening in Prevention of Mother-To-Child Transmission (PMTCT) programs is important to improve TB detection, prevention and treatment.

METHODS

As part of a national PMTCT program evaluation, mother-infant pairs attending 6-week and 9-month immunization visits were enrolled at 141 maternal and child health clinics throughout Kenya. Clinics were selected using population-proportion-to-size sampling with oversampling in a high human immunodeficiency virus (HIV) prevalence region. The World Health Organization (WHO) TB symptom screen was administered to HIV-infected mothers, and associations with infant cofactors were determined.

RESULTS

Among 498 HIV-infected mothers, 165 (33%) had a positive TB symptom screen. Positive maternal TB symptom screen was associated with prior TB (P = 0.04). Women with a positive TB symptom screen were more likely to have an infant with HIV infection (P = 0.02) and non-specific TB symptoms, including cough (P = 0.003), fever (P = 0.05), and difficulty breathing (P = 0.01). TB exposure was reported by 11% of the women, and 15% of the TB-exposed women received isoniazid preventive therapy.

CONCLUSIONS

Postpartum HIV-infected mothers frequently had a positive TB symptom screen. Mothers with a positive TB symptom screen were more likely to have infants with HIV or non-specific TB symptoms. Integration of maternal TB screening and prevention into PMTCT programs may improve maternal and infant outcomes.

Vitamin A and D Deficiencies Associated With Incident Tuberculosis in HIV-Infected Patients Initiating Antiretroviral Therapy in Multinational Case-Cohort Study

INTRODUCTION

Numerous micronutrients have immunomodulatory roles that may influence risk of tuberculosis (TB), but the association between baseline micronutrient deficiencies and incident TB after antiretroviral therapy (ART) initiation in HIV-infected individuals is not well characterized.

METHODS

We conducted a case-cohort study (n = 332) within a randomized trial comparing 3 ART regimens in 1571 HIV treatment-naive adults from 9 countries. A subcohort of 30 patients was randomly selected from each country (n = 270). Cases (n = 77; main cohort = 62, random subcohort = 15) included patients diagnosed with TB by 96 weeks post-ART initiation. We determined pretreatment concentrations of vitamin A, carotenoids, vitamin B6, vitamin B12, vitamin D, vitamin E, and selenium. We measured associations between pretreatment micronutrient deficiencies and incident TB using Breslow-weighted Cox regression models.

RESULTS

Median pretreatment CD4 T-cell count was 170 cells/mm; 47.3% were women; and 53.6% Black. In multivariable models after adjusting for age, sex, country, treatment arm, previous TB, baseline CD4 count, HIV viral load, body mass index, and C-reactive protein, pretreatment deficiency in vitamin A (adjusted hazard ratio, aHR 5.33, 95% confidence interval, CI: 1.54 to 18.43) and vitamin D (aHR 3.66, 95% CI: 1.16 to 11.51) were associated with TB post-ART.

CONCLUSIONS

In a diverse cohort of HIV-infected adults from predominantly low- and middle-income countries, deficiencies in vitamin A and vitamin D at ART initiation were independently associated with increased risk of incident TB in the ensuing 96 weeks. Vitamin A and D may be important modifiable risk factors for TB in high-risk HIV-infected patients starting ART in resource-limited highly-TB-endemic settings.

Mycobacterium bovis BCG and New Vaccines for the Prevention of Tuberculosis

Tuberculosis infects millions of people worldwide and remains a leading global killer despite widespread neonatal administration of the tuberculosis vaccine, bacillus Calmette-Guérin (BCG). BCG has clear and sustained efficacy, but after 10 years, its efficacy appears to wane, at least in some populations. Fortunately, there are many new tuberculosis vaccines in development today, some in advanced stages of clinical trial testing. Here we review the epidemiological need for tuberculosis vaccination, including evolving standards for administration to at risk individuals in developing countries. We also examine proven sources of immune protection from tuberculosis, which to date have exclusively involved natural or vaccine exposure to whole cell mycobacteria. After summarizing evidence for the use and efficacy of BCG, we detail the most promising new candidate vaccines against tuberculosis. The global need for a new tuberculosis vaccine is acute and huge, but clinical trials to be completed in the coming few years are likely either to identify a new tuberculosis vaccine or to substantially reframe how we understand immune protection from this historical scourge.

Predictors and short-term outcomes of recurrent pulmonary tuberculosis, Uganda: a cohort study

INTRODUCTION

Recurrent tuberculosis (TB) occurring >2 years after completing treatment for a prior TB episode is most often due to reinfection with a new strain of M. tuberculosis.

OBJECTIVES

We determined the prevalence and outcome of late recurrent TB among hospitalized patients in Kampala, Uganda.

METHODS

We conducted a retrospective analysis of patients admitted to Mulago Hospital who had cough of >2 weeks' duration and completed TB treatment >2 years prior to admission. All patients had mycobacterial culture performed on two sputum specimens and vital status ascertained 2-months post-enrollment. We performed modeling to identify predictors of recurrent TB and of survival.

RESULTS

Among 234 patients, 84 (36%) had recurrent TB. Independent predictors included younger age (aOR=0.64, 95% CI=0.42-0.97, p=0.04), chest pain >2 weeks (aOR=3.32, 95% CI=1.38-8.02, p=0.007), severe weight loss ≥5 kilograms (aOR=4.88, 95% CI=1.66-14.29, p=0.004) and presence of ≥1 WHO danger sign of severe illness (aOR=3.55, 95% CI=1.36-9.29, p=0.01). Two-month mortality was 17.8% (95% CI=10.5-29.2%), and was higher among patients not initiated on TB treatment (aHR=16.67, 95% CI=1.18-200, p=0.04), not on ART if HIV-positive (aHR=16.99, 95% CI=1.17-246.47, p=0.04) and with a history of smoking (aHR=1.20, 95% CI=1.03-1.40, p=0.02).

CONCLUSION

The high prevalence of late recurrent TB likely reflects high levels of TB transmission in Kampala. Increased use of empiric TB treatment and early ART treatment initiation if HIV-positive should be considered in patients with a prior history of TB, particularly if young, with weight loss ≥5kgs, chest pain >2 weeks or ≥1 WHO danger sign of severe illness.

Mapping of Mycobacterium tuberculosis Complex Genetic Diversity Profiles in Tanzania and Other African Countries

The aim of this study was to assess and characterize Mycobacterium tuberculosis complex (MTBC) genotypic diversity in Tanzania, as well as in neighbouring East and other several African countries. We used spoligotyping to identify a total of 293 M. tuberculosis clinical isolates (one isolate per patient) collected in the Bunda, Dar es Salaam, Ngorongoro and Serengeti areas in Tanzania. The results were compared with results in the SITVIT2 international database of the Pasteur Institute of Guadeloupe. Genotyping and phylogeographical analyses highlighted the predominance of the CAS, T, EAI, and LAM MTBC lineages in Tanzania. The three most frequent Spoligotype International Types (SITs) were: SIT21/CAS1-Kili (n = 76; 25.94%), SIT59/LAM11-ZWE (n = 22; 7.51%), and SIT126/EAI5 tentatively reclassified as EAI3-TZA (n = 18; 6.14%). Furthermore, three SITs were newly created in this study (SIT4056/EAI5 n = 2, SIT4057/T1 n = 1, and SIT4058/EAI5 n = 1). We noted that the East-African-Indian (EAI) lineage was more predominant in Bunda, the Manu lineage was more common among strains isolated in Ngorongoro, and the Central-Asian (CAS) lineage was more predominant in Dar es Salaam (p-value<0.0001). No statistically significant differences were noted when comparing HIV status of patients vs. major lineages (p-value = 0.103). However, when grouping lineages as Principal Genetic Groups (PGG), we noticed that PGG2/3 group (Haarlem, LAM, S, T, and X) was more associated with HIV-positive patients as compared to PGG1 group (Beijing, CAS, EAI, and Manu) (p-value = 0.03). This study provided mapping of MTBC genetic diversity in Tanzania (containing information on isolates from different cities) and neighbouring East African and other several African countries highlighting differences as regards to MTBC genotypic distribution between Tanzania and other African countries. This work also allowed underlining of spoligotyping patterns tentatively grouped within the newly designated EAI3-TZA lineage (remarkable by absence of spacers 2 and 3, and represented by SIT126) which seems to be specific to Tanzania. However, further genotyping information would be needed to confirm this specificity.

The timing of tuberculosis after isoniazid preventive therapy among gold miners in South Africa: a prospective cohort study

BACKGROUND

The durability of isoniazid preventive therapy (IPT) in preventing tuberculosis (TB) is limited in high-prevalence settings. The underlying mechanism (reactivation of persistent latent TB or reinfection) is not known. We aimed to investigate the timing of TB incidence during and after IPT and associated risk factors in a very high TB and HIV-prevalence setting, and to compare the observed rate with a modelled estimate of TB incidence rate after IPT due to reinfection.

METHODS

In a post-hoc analysis of a cluster-randomized trial of community-wide IPT among South African gold miners, all intervention arm participants that were dispensed IPT for at least one of the intended 9 months were included. An incident TB case was defined as any participant with a positive sputum smear or culture, or with a clinical TB diagnosis assigned by a senior study clinician. Crude TB incidence rates were calculated during and after IPT, overall and by follow-up time. HIV status was not available. Multivariable Cox regression was used to analyse risk factors by follow-up time after IPT. Estimates from a published mathematical model of trial data were used to calculate the average reinfection TB incidence in the first year after IPT.

RESULTS

Among 18,520 participants (96% male, mean age 41 years, median follow-up 2.1 years), 708 developed TB. The TB incidence rate during the intended IPT period was 1.3/100 person-years (pyrs; 95% confidence interval (CI), 1.0-1.6) and afterwards 2.3/100 pyrs (95% CI, 1.9-2.7). TB incidence increased within 6 months followed by a stable rate over time. There was no evidence for changing risk factors for TB disease over time after miners stopped IPT. The average TB incidence rate attributable to reinfection in the first year was estimated at 1.3/100 pyrs, compared to an observed rate of 2.2/100 pyrs (95% CI, 1.8-2.7).

CONCLUSIONS

The durability of protection by IPT was lost within 6-12 months in this setting with a high HIV prevalence and a high annual risk of M. tuberculosis infection. The observed rate was higher than the modelled rate, suggesting that reactivation of persistent latent infection played a role in the rapid return to baseline TB incidence.

A systematic review of published literature describing factors associated with tuberculosis recurrence in people living with HIV in Africa

BACKGROUND

A summary of factors associated with recurrent tuberculosis (TB) in the African HIV-infected population is lacking. We performed a systematic review to address this.

METHODS

We performed a literature search within PubMed and The WHO Global Library with specific inclusion and exclusion criteria to identify manuscripts emanating from the African continent which potentially described factors associated with recurrent TB in persons living with HIV.

RESULTS

The literature search yielded 52 unique manuscripts, of which only 4 manuscripts were included in the final systematic review following application of the inclusion and exclusion criteria. Baseline CD4 count, baseline HIV viral load, a positive tuberculin skin test, prior active TB disease, cutaneous hypersensitivity reaction to treatment, having < 3 lung zones affected by prior TB disease, and anaemia were associated with recurrent TB in HIV-infected individuals, whilst age and antiretroviral status were not.

CONCLUSION

The lack of studies describing recurrent TB in Africa which stratify results by HIV-status is a hindrance to understanding risk factors for recurrent TB in this population. This might be overcome by implementing guidelines related to the publishing of data from observational studies in peer-reviewed medical journals reporting recurrent TB in populations with a high-burden of HIV infection.

Effect of isoniazid preventive therapy on tuberculosis or death in persons with HIV: a retrospective cohort study

Background

Isoniazid preventive therapy (IPT) is a recommended strategy for prevention of tuberculosis (TB) in persons with Human Immunodeficiency Virus (HIV) although the benefits have not been unequivocally demonstrated in routine clinical practice with widespread ART adoption. Therefore, we assessed the effectiveness of IPT in prevention of TB or death in patients treated with antiretroviral therapy (ART) in a chronic care setting.

Methods

Retrospective cohort study of HIV patients enrolled in chronic care from 2007 to 2013. Eligible participants were HIV infected subjects (age > 15 years) with no (history of) TB. The combined effect of IPT and ART on the composite outcome (TB or death) was estimated using time-dependent Cox regression with adjustment for baseline covariates.

Results

1,922 patients were included, 374 (19.4 %) received IPT and 258 (13.4 %) developed TB or deceased. The median follow-up duration of the cohort was 839 days, with a total of 5491 person years. In unadjusted analysis, the combination of IPT and ART lowered the hazard of TB or death by 65 % [HR = 0.35; 95 % CI (0.16, 0.77)] compared to ART alone. Even after adjustment for confounders, the combined effect of ART and IPT resulted in a 60 % hazard reduction of TB or death in comparison to participants who received ART without IPT [HR = 0.40; 95 % CI (0.18, 0.87)]. The IPT-specific benefit in patients not receiving ART could not be reliably estimated due to high rates of ART adoption.

Conclusion

The combined effect of IPT and ART to prevent TB or death in HIV patients in a non-experimental setting in comparison to ART alone was estimated to be 60 %.

Risk of tuberculosis among HAART receiving HIV patients attending an ART centre of West Bengal, India: a prospective cohort study

This prospective study was conducted to find out the incidence density rate and to identify the attributed risk factors of Tuberculosis development among ART receivers. All patients who were registered in a nodal ART centre of India within 1st January 2008-31st December 2008 and had been initiated ART in the year of 2008 were considered as a cohort and were followed up till 31st December 2012. This study was started with 169 ART receivers and ended with 129 patients. During total 631.1 person-years observation, 39 TB cases (31 pulmonary and 8 extra pulmonary) were diagnosed. TB incidence density rate reduced from 12.08/100 to 1.12/100 person-years during the follow up periods. Cox regression model revealed that patients having past history of Tuberculosis were at 5 times higher risk (Hazard ratio = 5.205; 95 % CI 2.439-11.106; p = 0.000). Patients with WHO clinical stage 3 or 4 at the time of enrolment had 2 times more risk of development of TB (Hazard ratio = 2.081; 95 % CI 1.502-2.884; p = 0.000). This study highlighted that special attention should be paid on earliest identification of TB among the HIV patients who had past history of TB or suffering from WHO clinical stage 3 or 4 to prevent the silent transmission and multidrug resistance development of Tuberculosis in the community.

Use of isoniazid preventive therapy for tuberculosis prophylaxis among people living with HIV/AIDS: a review of the literature

BACKGROUND

Tuberculosis (TB) is the leading preventable cause of death in persons living with HIV (PLHIV), accounting for over a quarter of all HIV-associated deaths in 2012. Isoniazid preventive therapy (IPT) has the potential to decrease TB-related cases and deaths in PLHIV; however, implementation of this has been slow in many high HIV- and TB-burden settings.

METHODOLOGY

We performed an assessment of the evidence for the use of IPT in adults living with HIV based on a review of the literature published from 1995 to 2013. Eligible articles included data on mortality, morbidity, or retention in care related to the provision of IPT to adults with HIV in low- or middle-income countries. Cost-effectiveness information was also abstracted.

RESULTS

We identified 41 articles involving over 45,000 PLHIV. While there was little evidence to demonstrate that IPT reduced mortality in PLHIV, there was substantial evidence that IPT reduced TB incidence. While these findings were consistent irrespective of CD4 or antiretroviral therapy status, studies frequently demonstrated a greater benefit among patients with a positive TB skin test (TST). Duration of effectiveness and benefits of prolonged therapy varied across settings.

CONCLUSIONS

This analysis supports World Health Organization recommendations for the provision of IPT to PLHIV to reduce TB-associated morbidity and serves to highlight the need to strengthen IPT implementation. While there appears to be a greater benefit of IPT among PLHIV who are TST positive, IPT should be provided to all PLHIV without presumptive TB when TST is not available.

Active case finding for tuberculosis among people who inject drugs on methadone treatment in Dar es Salaam, Tanzania

SETTING

Active case finding is a World Health Organization (WHO) endorsed strategy for improving tuberculosis (TB) case detection. Despite WHO recommendations for active case finding among people who inject drugs (PWID), few studies have been published. The historical focus of case finding has been in populations that are human immunodeficiency virus-positive, incarcerated or at higher occupational risk.

OBJECTIVE

We sought to examine the yield of active case finding among PWID newly started on methadone in Tanzania.

DESIGN

Of 222 methadone clients, 156 (70%) met with study administrators; 150 consented to participate, 139 (93%) of whom were male. The median age was 34 years. A symptom-based questionnaire was developed by the investigators and administered to every consenting patient by a native Swahili speaker.

RESULTS

Of the 150 patients surveyed, 16 (11%) had one or more TB symptoms and were referred for laboratory testing. Six new TB cases were identified in this active case finding program, with a prevalence of 4%.

CONCLUSION

This study presents the first data on TB prevalence in a population of PWID in Tanzania. This prevalence is 23 times that of the general Tanzanian TB prevalence of 0.2%. These results have significant implications for TB control.

The re-emergence of tuberculosis: what have we learnt from molecular epidemiology?

Tuberculosis (TB) has re-emerged over the past two decades: in industrialized countries in association with immigration, and in Africa owing to the human immunodeficiency virus epidemic. Drug-resistant TB is a major threat worldwide. The variable and uncertain impact of TB control necessitates not only better tools (diagnostics, drugs, and vaccines), but also better insights into the natural history and epidemiology of TB. Molecular epidemiological studies over the last two decades have contributed to such insights by answering long-standing questions, such as the proportion of cases attributable to recent transmission, risk factors for recent transmission, the occurrence of multiple Mycobacterium tuberculosis infection, and the proportion of recurrent TB cases attributable to re-infection. M. tuberculosis lineages have been identified and shown to be associated with geographical origin. The Beijing genotype is strongly associated with multidrug resistance, and may have escaped from bacille Calmette-Guérin-induced immunity. DNA fingerprinting has quantified the importance of institutional transmission and laboratory cross-contamination, and has helped to focus contact investigations. Questions to be answered in the near future with whole genome sequencing include identification of chains of transmission within clusters of patients, more precise quantification of mixed infection, and transmission probabilities and rates of progression from infection to disease of various M. tuberculosis lineages, as well as possible variations in vaccine efficacy by lineage. Perhaps most importantly, dynamics in the population structure of M. tuberculosis in response to control measures in high-prevalence areas should be better understood.