Tuberculosis epidemics driven by HIV: is prevention better than cure?

A yield and cost comparison of tuberculosis contact investigation and intensified case finding in Uganda

INTRODUCTION

Resource constraints in Low and Middle-Income Countries (LMICs) limit tuberculosis (TB) contact investigation despite evidence its benefits could outweigh costs, with increased efficiency when compared with intensified case finding (ICF). However, there is limited data on yield and cost per TB case identified. We compared yield and cost per TB case identified for ICF and Tuberculosis-Contact Investigation (TB-CI) in Uganda.

METHODS

A retrospective cohort study based on data from 12 Ugandan hospitals was done between April and September 2017. Two methods of TB case finding (i.e. ICF and TB-CI) were compared. Regarding ICF, patients either self-reported their signs and symptoms or were prompted by health care workers, while TB-CI was done by home-visiting and screening contacts of TB patients. Patients who were presumed to have tuberculosis were requested to produce a sample for examination. TB yield was defined as a ratio of diagnoses to tests, and this was computed per method of diagnosis. The cost per TB case identified (medical, personnel, transportation and training) for each diagnosis method were computed using the activity-based approach, from the health care perspective. Cost data were analyzed using Windows Excel.

RESULTS

454 index TB cases and 2,707 of their household contacts were investigated. Thirty-one per cent of contacts (840/2707) were found to be presumptive TB cases. A total of 7,685 tests were done, 6,967 for ICF and 718 for TB-CI. The yields were 18.62% (1297/6967) and 5.29% (38/718) for ICF and TB-CI, respectively. It cost US$ 120.60 to diagnose a case of TB using ICF compared to US$ 877.57 for TB-CI.

CONCLUSION

The yield of TB-CI was found to be four-times lower and seven-times costlier compared to ICF. These findings suggest that ICF can improve TB case detection at a low cost, particularly in high TB prevalent settings.

Tuberculosis decline in populations affected by HIV: a retrospective study of 12 countries in the WHO African Region

Objective

To investigate which of the World Health Organization recommended methods for tuberculosis control have had the greatest effect on case incidence in 12 countries in the World Health Organization (WHO) African Region that carry high burdens of tuberculosis linked to human immunodeficiency virus (HIV) infection.

Methods

We obtained epidemiological surveillance, survey and treatment data on HIV and tuberculosis for the years 2003 to 2016. We used statistical models to examine the effects of antiretroviral therapy (ART) and isoniazid preventive therapy in reducing the incidence of tuberculosis among people living with HIV. We also investigated the role of tuberculosis case detection and treatment in preventing Mycobacterium tuberculosis transmission and consequently reducing tuberculosis incidence.

Findings

Between 2003 and 2016, ART provision was associated with the decline of tuberculosis in each country, and with differences in tuberculosis decline between countries. Inferring that ART was a cause of tuberculosis decline, ART prevented 1.88 million (95% confidence interval, CI: 1.65 to 2.11) tuberculosis cases in people living with HIV, or 15.7% (95% CI: 13.8 to 17.6) of the 11.96 million HIV-positive tuberculosis cases expected. Population coverage of isoniazid preventive therapy was too low (average 1.0% of persons eligible) to have a major effect on tuberculosis decline, and improvements in tuberculosis detection and treatment were either weakly associated or not significantly associated with tuberculosis decline.

Conclusion

ART provision is associated with tuberculosis decline in these 12 countries. ART should remain central to tuberculosis control where rates of tuberculosis–HIV coinfection are high, but renewed efforts to treat tuberculosis are needed.

Diagnosing active and latent tuberculosis among Iranian HIV-infected patients

OBJECTIVE

To screen for Tuberculosis (TB) in human immunodeficiency virus (HIV) people in an effort to improve early TB diagnosis and reduce TB transmission.

METHODS

A prospective study was conducted on adult HIV people from 2008 to 2011. Three samples of sputum, cell blood count, tuberculin skin test (TST) and chest X-ray were obtained from all patients. The characteristics of HIV patients with TB and HIV patients without TB were compared to each other.

RESULTS

Of the 154 HIV patients included, 58 (38%) had tuberculosis with a mean CD4 cell count of 68 cells/mm³ . Active TB was found in 56 (47%) patients with a history of intravenous drug use. Cough (OR = 3.1, 95% CI 1.2-7.79), positive TST (OR = 8.15, 95% CI 3.28-20.25) and an abnormal chest X-ray (OR = 5.1, 95% CI 1.84-14.2) were the predicting factors for detecting active TB among HIV patients. The sensitivity and specificity of a combination of any symptoms with chest X-ray, smear, TST or all of these were 96.5% and 86.5%, respectively. CD4 cell count <100 (OR = 2.67; 95% CI 1.23-5.78) and smoking (OR = 13.4; 95% CI 3.04-59.4) remained independently associated with TB in a multivariate analysis.

CONCLUSION

There was a high prevalence of TB within the HIV population. Screening for TB among these patients can be carried out at every clinic or health facility using a combination of symptoms, TST, chest X-ray and smear sample.

The impact of migration on tuberculosis epidemiology and control in high-income countries: a review

Tuberculosis (TB) causes significant morbidity and mortality in high-income countries with foreign-born individuals bearing a disproportionate burden of the overall TB case burden in these countries. In this review of tuberculosis and migration we discuss the impact of migration on the epidemiology of TB in low burden countries, describe the various screening strategies to address this issue, review the yield and cost-effectiveness of these programs and describe the gaps in knowledge as well as possible future solutions.The reasons for the TB burden in the migrant population are likely to be the reactivation of remotely-acquired latent tuberculosis infection (LTBI) following migration from low/intermediate-income high TB burden settings to high-income, low TB burden countries.TB control in high-income countries has historically focused on the early identification and treatment of active TB with accompanying contact-tracing. In the face of the TB case-load in migrant populations, however, there is ongoing discussion about how best to identify TB in migrant populations. In general, countries have generally focused on two methods: identification of active TB (either at/post-arrival or increasingly pre-arrival in countries of origin) and secondly, conditionally supported by WHO guidance, through identifying LTBI in migrants from high TB burden countries. Although health-economic analyses have shown that TB control in high income settings would benefit from providing targeted LTBI screening and treatment to certain migrants from high TB burden countries, implementation issues and barriers such as sub-optimal treatment completion will need to be addressed to ensure program efficacy.

Bioeconomic analysis of child-targeted subsidies for artemisinin combination therapies: a cost-effectiveness analysis

The Affordable Medicines Facility for malaria (AMFm) was conceived as a global market-based mechanism to increase access to effective malaria treatment and prolong effectiveness of artemisinin. Although results from a pilot implementation suggested that the subsidy was effective in increasing access to high-quality artemisinin combination therapies (ACTs), the Global Fund has converted AMFm into a country-driven mechanism whereby individual countries could choose to fund the subsidy from within their country envelopes. Because the initial costs of the subsidy in the pilot countries was higher than expected, countries are also exploring alternatives to a universal subsidy, such as subsidizing only child doses. We examined the incremental cost-effectiveness of a child-targeted policy using an age-structured bioeconomic model of malaria from the provider perspective. Because the vast majority of malaria deaths occur in children, targeting children could potentially improve the cost-effectiveness of the subsidy, though it would avert significantly fewer deaths. However, the benefits of a child-targeted subsidy (i.e. deaths averted) are eroded as leakage (i.e. older individuals taking young child-targeted doses) increases, with few of the benefits of a universal subsidy gained (i.e. reductions in overall prevalence). Although potentially more cost-effective, a child-targeted subsidy must contain measures to reduce the possibility of leakage.

Evaluating the potential impact of enhancing HIV treatment and tuberculosis control programmes on the burden of tuberculosis

HIV has fuelled increasing tuberculosis (TB) incidence in sub-Saharan Africa. Better control of TB in this region may be achieved directly through TB programme improvements and indirectly through expanded use of antiretroviral therapy (ART) among those with HIV. We used a mathematical model of TB and HIV in South Africa to examine the potential epidemiological impact in scenarios involving improvements in three dimensions of TB programmes: coverage, diagnosis and treatment effectiveness, as well as expanded ART use through broadened eligibility. We projected the effect of alternative scenarios on TB prevalence, incidence and TB-related mortality over 20 years. Of the three dimensions of TB programme improvement, expanding coverage would produce the greatest reduction in TB burden. Compared with current performance, combined TB programme improvements were projected to decrease TB incidence by 30% over 5 years and 46% over 20 years, and decrease TB-related mortality by 45% over 5 years and 69% over 20 years. Expanded ART eligibility was projected to decrease TB incidence by 22% over 5 years and 45% over 20 years, and TB-related mortality by 22% over 5 years and 50% over 20 years. We found that over a 20-year horizon, TB-specific and HIV-specific programme changes contribute equally to incidence reductions, whereas the TB-specific changes produce a majority of the mortality benefits. An aggressive expansion of ART alongside traditional TB-specific control measures has the potential to greatly reduce TB burden, with the different elements of a combined approach having a synergistic effect in reducing long-term TB incidence and mortality.

Effect of antiretroviral treatment on the risk of tuberculosis during South Africa's programme expansion

OBJECTIVE

The objective of this study is to estimate the effectiveness of antiretroviral treatment (ART) in preventing tuberculosis (TB) in HIV-infected people during the first 6 years of ART programme expansion.

DESIGN

A cohort study comparing TB risk without ART and after ART initiation.

SETTING

Public sector HIV programme of the Free State province, South Africa.

PARTICIPANTS

Seventy-four thousand and seventy-four HIV-infected people enrolled from 2004 until 2010, of whom 43 898 received ART and 30 176 did not.

INTERVENTION

Combination ART.

MAIN OUTCOME MEASURES

Time to first TB diagnosis, adjusted for CD4 cell count, weight, age, sex, previous TB, district and year, with ART, CD4 cell count and weight as time-varying covariates and with death as a competing risk.

RESULTS

Three thousand eight hundred and fifty-eight first TB episodes occurred during 78 202 person-years at risk with ART and 5669 episodes occurred during 62 801 person-years without ART [incidence rates 4.9 and 9.0 per 100 person-years, crude incidence rate ratio 0.55 (95% confidence interval 0.52-0.57)]. The adjusted subhazard ratio (SHR) of time to first TB episode after starting ART, compared with follow-up without ART, was 0.67 (0.64-0.70). Within CD4 cell count subgroups (<50, 50-199, 100-199, 200-349 and >350 cells/μl), the respective SHRs were 0.64 (0.57-0.71), 0.63 (0.57-0.70), 0.66 (0.61-0.72), 0.67 (0.62-0.72), 0.72 (0.63-0.83) and 0.97 (0.60-1.59). Adjusted SHRs for ART decreased with each year of enrolment, from 0.90 (0.77-1.04) in 2004 to 0.54 (0.43-0.67) in 2010.

CONCLUSION

ART was effective in preventing TB in HIV-infected patients with CD4 cell counts below 350 cells/μl, but less so than previously estimated. Effectiveness increased each year.

Integrating Community-Based Interventions to Reverse the Convergent TB/HIV Epidemics in Rural South Africa

The WHO recommends integrating interventions to address the devastating TB/HIV co-epidemics in South Africa, yet integration has been poorly implemented and TB/HIV control efforts need strengthening. Identifying infected individuals is particularly difficult in rural settings. We used mathematical modeling to predict the impact of community-based, integrated TB/HIV case finding and additional control strategies on South Africa’s TB/HIV epidemics. We developed a model incorporating TB and HIV transmission to evaluate the effectiveness of integrating TB and HIV interventions in rural South Africa over 10 years. We modeled the impact of a novel screening program that integrates case finding for TB and HIV in the community, comparing it to status quo and recommended TB/HIV control strategies, including GeneXpert, MDR-TB treatment decentralization, improved first-line TB treatment cure rate, isoniazid preventive therapy, and expanded ART. Combining recommended interventions averted 27% of expected TB cases (95% CI 18–40%) 18% HIV (95% CI 13–24%), 60% MDR-TB (95% CI 34–83%), 69% XDR-TB (95% CI 34–90%), and 16% TB/HIV deaths (95% CI 12–29). Supplementing these interventions with annual community-based TB/HIV case finding averted a further 17% of TB cases (44% total; 95% CI 31–56%), 5% HIV (23% total; 95% CI 17–29%), 8% MDR-TB (68% total; 95% CI 40–88%), 4% XDR-TB (73% total; 95% CI 38–91%), and 8% TB/HIV deaths (24% total; 95% CI 16–39%). In addition to increasing screening frequency, we found that improving TB symptom questionnaire sensitivity, second-line TB treatment delays, default before initiating TB treatment or ART, and second-line TB drug efficacy were significantly associated with even greater reductions in TB and HIV cases. TB/HIV epidemics in South Africa were most effectively curtailed by simultaneously implementing interventions that integrated community-based TB/HIV control strategies and targeted drug-resistant TB. Strengthening existing TB and HIV treatment programs is needed to further reduce disease incidence.

A double age-structured model of the co-infection of tuberculosis and HIV

After decades on the decline, it is believed that the emergence of HIV is responsible for an increase in the tuberculosis prevalence. The leading infectious disease in the world, tuberculosis is also the leading cause of death among HIV-positive individuals. Each disease progresses through several stages. The current model suggests modeling these stages through a time-since-infection tracking transmission rate function, which, when considering co-infection, introduces a double-age structure in the PDE system. The basic and invasion reproduction numbers for each disease are calculated and the basic ones established as threshold for the disease progression. Numerical results confirm the calculations and a simple treatment scenario suggests the importance of time-since-infection when introducing disease control and treatment in the model.

The potential effects of changing HIV treatment policy on tuberculosis outcomes in South Africa: results from three tuberculosis-HIV transmission models

OBJECTIVE(S)

Many countries are considering expanding HIV treatment following recent findings emphasizing the effects of antiretroviral therapy (ART) on reducing HIV transmission in addition to already established survival benefits. Given the close interaction of tuberculosis (TB) and HIV epidemics, ART expansion could have important ramifications for TB burden. Previous studies suggest a wide range of possible TB impacts following ART expansion. We used three independently developed TB-HIV models to estimate the TB-related impact of expanding ART in South Africa.

DESIGN

We considered two dimensions of ART expansion--improving coverage of pre-ART and ART services, and expanding CD4-based ART eligibility criteria (from CD4 <350 to CD4 <500 or all HIV-positive).

METHODS

Three independent mathematical models were calibrated to the same data pertaining to the South African HIV-TB epidemic, and used to assess standardized ART policy changes. Key TB impact indicators were projected from 2014 to 2033.

RESULTS

Compared with current eligibility and coverage, cumulative TB incidence was projected to decline by 6-30% over the period 2014-2033 if ART eligibility were expanded to all HIV positive individuals, and by 28-37% if effective ART coverage were additionally increased to 80%. Overall, expanding ART was estimated to avert one TB case for each 10-13 additional person-years of ART. All models showed that TB incidence and mortality reductions would grow over time, but would stabilize towards the end of the projection period.

CONCLUSION

ART expansion could substantially reduce TB incidence and mortality in South Africa and could provide a platform for collaborative HIV-TB programs to effectively halt HIV-associated TB.

Identifying dynamic tuberculosis case-finding policies for HIV/TB coepidemics

The global tuberculosis (TB) control plan has historically emphasized passive case finding (PCF) as the most practical approach for identifying TB suspects in high burden settings. The success of this approach in controlling TB depends on infectious individuals recognizing their symptoms and voluntarily seeking diagnosis rapidly enough to reduce onward transmission. It now appears, at least in some settings, that more intensified case-finding (ICF) approaches may be needed to control TB transmission; these more aggressive approaches for detecting as-yet undiagnosed cases obviously require additional resources to implement. Given that TB control programs are resource constrained and that the incremental yield of ICF is expected to wane over time as the pool of undiagnosed cases is depleted, a tool that can help policymakers to identify when to implement or suspend an ICF intervention would be valuable. In this article, we propose dynamic case-finding policies that allow policymakers to use existing observations about the epidemic and resource availability to determine when to switch between PCF and ICF to efficiently use resources to optimize population health. Using mathematical models of TB/HIV coepidemics, we show that dynamic policies strictly dominate static policies that prespecify a frequency and duration of rounds of ICF. We also find that the use of a diagnostic tool with better sensitivity for detecting smear-negative cases (e.g., Xpert MTB/RIF) further improves the incremental benefit of these dynamic case-finding policies.

Mathematical models of the epidemiology and control of drug-resistant TB

Recent reports of extensively drug-resistant TB in South Africa have renewed concerns that antibiotic resistance may undermine progress in TB control. We review three major questions for which mathematical models elucidate the epidemiology and control of drug-resistant TB. How is multiple drug-resistant Mycobacterium tuberculosis selected for in individuals exposed to combination chemotherapy? What factors determine the prevalence of drug-resistant TB? Which interventions to prevent the spread of drug-resistant TB are effective and feasible? Models offer insight into the acquisition and amplification of drug resistance, reveal the importance of distinguishing the intrinsic and extrinsic determinants of the reproductive capacity of drug-resistant M. tuberculosis, and demonstrate the cost effectiveness of interventions for drug-resistant TB. These models also highlight knowledge gaps for which new research will improve our ability to project trends of drug resistance and develop more effective policies for its control.

Modeling the dynamic relationship between HIV and the risk of drug-resistant tuberculosis

The emergence of highly drug-resistant tuberculosis (TB) and interactions between TB and HIV epidemics pose serious challenges for TB control. Previous researchers have presented several hypotheses for why HIV-coinfected TB patients may suffer an increased risk of drug-resistant TB (DRTB) compared to other TB patients. Although some studies have found a positive association between an individual's HIV status and his or her subsequent risk of multidrug-resistant TB (MDRTB), the observed individual-level relationship between HIV and DRTB varies substantially among settings. Here, we develop a modeling framework to explore the effect of HIV on the dynamics of DRTB. The model captures the acquisition of resistance to important classes of TB drugs, imposes fitness costs associated with resistance-conferring mutations, and allows for subsequent restoration of fitness because of compensatory mutations. Despite uncertainty in several key parameters, we demonstrate epidemic behavior that is robust over a range of assumptions. Whereas HIV facilitates the emergence of MDRTB within a community over several decades, HIV-seropositive individuals presenting with TB may, counterintuitively, be at lower risk of drug-resistant TB at early stages of the co-epidemic. This situation arises because many individuals with incident HIV infection will already harbor latent Mycobacterium tuberculosis infection acquired at an earlier time when drug resistance was less prevalent. We find that the rise of HIV can increase the prevalence of MDRTB within populations even as it lowers the average fitness of circulating MDRTB strains compared to similar populations unaffected by HIV. Preferential social mixing among individuals with similar HIV status and lower average CD4 counts among HIV-seropositive individuals further increase the expected burden of MDRTB. This model suggests that the individual-level association between HIV and drug-resistant forms of TB is dynamic, and therefore, cross-sectional studies that do not report a positive individual-level association will not provide assurance that HIV does not exacerbate the burden of resistant TB in the community.

High prevalence of pulmonary tuberculosis and inadequate case finding in rural western Kenya

RATIONALE

Limited information exists on the prevalence of tuberculosis and adequacy of case finding in African populations with high rates of HIV.

OBJECTIVES

To estimate the prevalence of bacteriologically confirmed pulmonary tuberculosis (PTB) and the fraction attributable to HIV, and to evaluate case detection.

METHODS

Residents aged 15 years and older, from 40 randomly sampled clusters, provided two sputum samples for microscopy; those with chest radiograph abnormalities or symptoms suggestive of PTB provided one additional sputum sample for culture.

MEASUREMENTS AND MAIN RESULTS

PTB was defined by a culture positive for Mycobacterium tuberculosis or two positive smears. Persons with PTB were offered HIV testing and interviewed on care-seeking behavior. We estimated the population-attributable fraction of HIV on prevalent and notified PTB, the patient diagnostic rate, and case detection rate using provincial TB notification data. Among 20,566 participants, 123 had PTB. TB prevalence was 6.0/1,000 (95% confidence interval, 4.6-7.4) for all PTB and 2.5/1,000 (1.6-3.4) for smear-positive PTB. Of 101 prevalent TB cases tested, 52 (51%) were HIV infected, and 58 (64%) of 91 cases who were not on treatment and were interviewed had not sought care. Forty-eight percent of prevalent and 65% of notified PTB cases were attributable to HIV. For smear-positive and smear-negative PTB combined, the patient diagnostic rate was 1.4 cases detected per person-year among HIV-infected persons having PTB and 0.6 for those who were HIV uninfected, corresponding to case detection rates of 56 and 65%, respectively.

CONCLUSIONS

Undiagnosed PTB is common in this community. TB case finding needs improvement, for instance through intensified case finding with mobile smear microscopy services, rigorous HIV testing, and improved diagnosis of smear-negative TB.

Intensive phase non-compliance to anti tubercular treatment in patients with HIV-TB coinfection: a hospital-based cross-sectional study

We aimed to study the prevalence and determinants of non compliance to intensive phase anti tubercular treatment (ATT) in 111 HIV-TB coinfection patients, attending the APEX Referral Center for HIV/AIDS at Medical College, Kolkata with a specially-designed, semi-structured, pre-tested questionnaire. Compliance was defined as taking ≥95% of the total scheduled doses of anti-TB medicines during the intensive phase. Data was collected on socio-demographic parameters, disease information, patient's knowledge and barriers to treatment. The prevalence of non-compliance to ATT in HIV-TB coinfection patients was found to be 40.5% (95% C.I. = 30.5, 50.5). Multivariate logistic regression analysis showed that absence of proper counseling, lack of knowledge about correct route of TB transmission, visiting quacks during ATT and the urge to leave treatment once patient started feeling better were the significant determinants of non-compliance. "No Counseling" increased chances of non- compliance (adjusted O.R.) 47.12 times (95% C.I. = 7.99, 195.27); thereby being the single most influential variable towards the outcome. The present study finds an alarmingly high prevalence of non-compliance to ATT among HIV-TB coinfection patients. The results clearly indicate that adequate counseling about this coinfection and the importance of compliance, along with better patient-friendly orientation of DOTS programme is urgently needed. Collaborative TB-HIV activities are essential to ensure better ATT compliance in coinfection patients.

An investigation into the statistical properties of TB episodes in a South African community with high HIV prevalence

Continuous differential equations are often applied to small populations with little time spent on understanding uncertainty brought about by small-population effects. Despite large numbers of individuals being latently infected with Mycobacterium tuberculosis (TB), progression from latent infection to observable disease is a relatively rare event. For small communities, this means case counts are subject to stochasticity, and deterministic models may not be appropriate tools for interpreting transmission trends. Furthermore, the nonlinear nature of the underlying dynamics means that fluctuations are autocorrelated, which can invalidate standard statistical analyses which assume independent fluctuations. Here we extend recent work using a system of differential equations to study the HIV-TB epidemic in Masiphumelele, a community near Cape Town in South Africa [Bacaër, et al., J. Mol. Biol. 57(4), 557-593] by studying the statistical properties of active TB events. We apply van Kampen's system-size (or population-size) expansion technique to obtain an approximation to a master equation describing the dynamics. We use the resulting Fokker-Planck equation and point-process theory to derive two-time correlation functions for active TB events. This method can be used to gain insight into the temporal aspect of cluster identification, which currently relies on DNA classification only.

Antiretroviral program associated with reduction in untreated prevalent tuberculosis in a South African township

RATIONALE

In 2005, we reported high prevalence of untreated pulmonary tuberculosis (TB) in a South African community. Prevalent untreated TB is the main source of transmission. In settings with large burdens of human immunodeficiency virus (HIV) and TB, highly active antiretroviral therapy (HAART) may contribute to TB control.

OBJECTIVES

To assess the community-level impact of HAART on TB prevalence, we repeated a community-based TB prevalence cross-sectional survey in 2008 following HAART roll-out.

METHODS

A random 10% adult population sample was identified from the community. Participants provided two sputum specimens for acid-fast bacilli microscopy and TB culture. Oral transudate specimen was collected for anonymous HIV testing, linked to TB diagnosis. An interviewer-administered, structured questionnaire identified TB and HIV history and risk factors.

MEASUREMENTS AND MAIN RESULTS

In the 2008 survey, 1,250 adults participated (90% response rate); 306 (25%) tested HIV positive, of which 60 (20%) were receiving HAART. A total of 20 TB cases were identified (12 receiving TB treatment), representing a significant decline in prevalence from 3.2 to 1.6% (P = 0.02) between the surveys. TB prevalence in participants not infected with HIV was unchanged (P = 0.90). The decline occurred among participants not infected with HIV, decreasing from 9.2 to 3.6% in 2005 to 2008, respectively (P = 0.003). In participants infected with HIV, prevalence of treated TB declined from 4 to 2.3% (P = 0.06), and untreated TB prevalence from 5.2 to 1.3% (P = 0.02). The proportion of untreated TB in patients receiving HAART decreased significantly, from 22 to 0% (P < 0.001).

CONCLUSIONS

Prevalence of undiagnosed TB declined significantly over a period of increasing HAART availability. The decline was predominantly in individuals infected with HIV receiving HAART.

Cost-effectiveness of educational outreach to primary care nurses to increase tuberculosis case detection and improve respiratory care: economic evaluation alongside a randomised trial

OBJECTIVE

To evaluate the cost-effectiveness of an educational outreach intervention to improve primary respiratory care by South African nurses.

METHODS

Cost-effectiveness analysis alongside a pragmatic cluster randomised controlled trial, with individual patient data. The intervention, the Practical Approach to Lung Health in South Africa (PALSA), comprised educational outreach based on syndromic clinical practice guidelines for tuberculosis, asthma, chronic obstructive pulmonary disease, pneumonia and other respiratory diseases. The study included 1999 patients aged 15 or over with cough or difficult breathing, attending 40 primary care clinics staffed by nurses in the Free State province. They were interviewed at first presentation, and 1856 (93%) were interviewed 3 months later.

RESULTS

The intervention increased the tuberculosis case detection rate by 2.2% and increased the proportion of patients appropriately managed (that is, diagnosed with tuberculosis or prescribed an inhaled corticosteroid for asthma or referred with indicators of severe disease) by 10%. It costs the health service $68 more for each extra patient diagnosed with tuberculosis and $15 more for every extra patient appropriately managed. Analyses were most sensitive to assumptions about how long training was effective for and to inclusion of household and tuberculosis treatment costs.

CONCLUSION

This educational outreach method was more effective and more costly than usual training in improving tuberculosis, asthma and urgent respiratory care. The extra cost of increasing tuberculosis case detection was comparable to current costs of passive case detection. The syndromic approach increased cost-effectiveness by also improving care of other conditions. This educational intervention was sustainable, reaching thousands of health workers and hundreds of clinics since the trial.

HIV infection and tuberculosis in South Africa: an urgent need to escalate the public health response

One of the greatest challenges facing post-apartheid South Africa is the control of the concomitant HIV and tuberculosis epidemics. HIV continues to spread relentlessly, and tuberculosis has been declared a national emergency. In 2007, South Africa, with 0.7% of the world's population, had 17% of the global burden of HIV infection, and one of the world's worst tuberculosis epidemics, compounded by rising drug resistance and HIV co-infection. Until recently, the South African Government's response to these diseases has been marked by denial, lack of political will, and poor implementation of policies and programmes. Nonetheless, there have been notable achievements in disease management, including substantial improvements in access to condoms, expansion of tuberculosis control efforts, and scale-up of free antiretroviral therapy (ART). Care for acutely ill AIDS patients and long-term provision of ART are two issues that dominate medical practice and the health-care system. Decisive action is needed to implement evidence-based priorities for the control of the HIV and tuberculosis epidemics. By use of the framework of the Strategic Plans for South Africa for tuberculosis and HIV/AIDS, we provide prioritised four-step approaches for tuberculosis control, HIV prevention, and HIV treatment. Strong leadership, political will, social mobilisation, adequate human and financial resources, and sustainable development of health-care services are needed for successful implementation of these approaches.

Intensified tuberculosis case finding among HIV-Infected persons from a voluntary counseling and testing center in Addis Ababa, Ethiopia

OBJECTIVE

To evaluate commonly available screening tests for pulmonary tuberculosis (TB), using sputum bacteriology as a gold standard, in HIV-infected persons attending an urban voluntary counseling and testing clinic in Addis Ababa, Ethiopia.

DESIGN

Prospective enrollment of HIV-infected persons, all of whom underwent TB screening, regardless of symptoms, with: (1) symptom screening and physical examination, (2) 3 sputum specimens for smear microscopy, and (3) chest radiograph. One sputum was also sent for concentrated smear microscopy and mycobacterial culture. Chest radiographs were reviewed by 2 independent radiologists. A confirmed TB diagnosis was defined as 1 positive sputum smear and/or 1 positive sputum culture.

RESULTS

We enrolled 438 HIV-infected persons: 265 (61%) females, median age 34 years (range: 18-65), median CD4 cell count 181 cells per cubic millimeter (range: 2-1185). Overall, 32 (7%) persons were diagnosed with TB, of whom 5 (16%) were asymptomatic but culture-confirmed TB cases. Screening for cough >2 weeks would have detected only 12 (38%) confirmed TB cases; screening for cough or fever, of any duration, would have detected 24 (75%) cases, with specificity of 64%. Negative predictive value of screening for these 2 symptoms was 97%. Simulation of the current Ethiopian national guidelines had a sensitivity of 63% and specificity of 83% for diagnosing TB disease among study patients.

CONCLUSIONS

Traditional symptom screening is insufficient for detecting TB disease among HIV-infected persons but may serve to exclude TB disease. More sensitive, rapid, and low-cost diagnostic tests are needed to meet the demand of resource-limited settings.

How hepatitis D virus can hinder the control of hepatitis B virus

Background

Hepatitis D (or hepatitis delta) virus is a defective virus that relies on hepatitis B virus (HBV) for transmission; infection with hepatitis D can occur only as coinfection with HBV or superinfection of an existing HBV infection. Because of the bond between the two viruses, control measures for HBV may have also affected the spread of hepatitis D, as evidenced by the decline of hepatitis D in recent years. Since the presence of hepatitis D is associated with suppressed HBV replication and possibly infectivity, it is reasonable to speculate that hepatitis D may facilitate the control of HBV.

Methodology and Principal Findings

We introduced a mathematical model for the transmission of HBV and hepatitis D, where individuals with dual HBV and hepatitis D infection transmit both viruses. We calculated the reproduction numbers of single HBV infections and dual HBV and hepatitis D infections and examined the endemic prevalences of the two viruses. The results show that hepatitis D virus modulates not only the severity of the HBV epidemic, but also the impact of interventions for HBV. Surprisingly we find that the presence of hepatitis D virus may hamper the eradication of HBV. Interventions that aim to reduce the basic reproduction number of HBV below one may not be sufficient to eradicate the virus, as control of HBV depends also on the reproduction numbers of dual infections.

Conclusions and Significance

For populations where hepatitis D is endemic, plans for control programs ignoring the presence of hepatitis D may underestimate the HBV epidemic and produce overoptimistic results. The current HBV surveillance should be augmented with monitoring of hepatitis D, in order to improve accuracy of the monitoring and the efficacy of control measures.

Incongruent HIV and tuberculosis co-dynamics in Kenya: interacting epidemics monitor each other

OBJECTIVE

Kenya is heralded as an example of declining HIV in Africa, while its tuberculosis (TB) numbers continue rising. We conducted a comparative investigation of TB-HIV co-dynamics in Africa to determine the likelihood of reported trends.

METHODS AND RESULTS

Our mathematical modeling analysis exposes the notable incongruence of reported trends in Kenya because TB-HIV co-dynamics, tightly knit worldwide and most dramatically in sub-Saharan Africa, suggest that declining HIV trends should trigger reductions in TB trends. Moreover, a continental-scale analysis of TB-HIV trends places Kenya as an outlier in eastern and southern Africa, and shows TB outpacing HIV in western central Africa. We further investigate which TB processes across HIV stages have greater potential to reduce TB incidence via a sensitivity analysis.

CONCLUSIONS

There are two parsimonious explanations: an unaccounted improvement in TB case detection has occurred, or HIV is not declining as reported. The TB-HIV mismatch could be compounded by surveillance biases due to spatial heterogeneity in disease dynamics. Results highlight the need to re-evaluate trends of both diseases in Kenya, and identify the most critical epidemiological factors at play. Substantial demographic changes have occurred in Kenya, including rapid urbanization accompanied by poor living conditions, which could disproportionately increase TB incidence. Other possible contributors include immune reconstitution due to the recent delivery of antiretrovirals, and an increased presence of the virulent Beijing/W TB genotype. Results support the importance of integrating information from closely interacting epidemics, because this approach provides critical insights unobtainable when components of generalized epidemics are considered individually.

The theoretical influence of immunity between strain groups on the progression of drug-resistant tuberculosis epidemics

BACKGROUND

Emerging research suggests that genetically distinct strains of Mycobacterium tuberculosis may modulate the immune system differently. This may be of importance in high-burden settings where > or =1 genetic group of M. tuberculosis confers significant morbidity.

METHODS

A dynamic mathematical model was constructed to evaluate how different degrees of cross-immunity among M. tuberculosis groups could affect epidemics of drug-resistant tuberculosis (TB).

RESULTS

Simulated populations with immunogenically distinct TB strain groups experienced a heightened risk of drug-resistant TB, compared with populations without such strain diversity, even when the same rates of case detection and treatment success were achieved. The highest risks of infection were observed in populations in which HIV was prevalent. Drug-resistant strains with very low transmission fitness could still propagate in environments with reduced cross-immunity among different strain groups, even after common targets for case detection and treatment success are reached.

CONCLUSIONS

It is possible that the propagation of drug-resistant strains could depend not only on the rate of development of resistance and the fitness of the drug-resistant strains but, also, on the diversity of the strains in the region. The risk of infection with drug-resistant strains could be amplified in locations where there is reduced cross-immunity between originating strain groups. This amplification may be most profound during the first few decades of TB treatment expansion.

HIV and tuberculosis in Ho Chi Minh City, Vietnam, 1997-2002

An emerging HIV epidemic, concentrated in young, male, injection drug users, is responsible for increasing TB reporting rates in urban Vietnam.

In Ho Chi Minh City, Vietnam, reporting rates for tuberculosis (TB) are rising in an emerging HIV epidemic. To describe the HIV epidemic among TB patients and quantify its impact on rates of reported TB, we performed a repeated cross-sectional survey from 1997 through 2002 in a randomly selected sample of inner city TB patients. We assessed effect by adjusting TB case reporting rates by the fraction of TB cases attributable to HIV infection. HIV prevalence in TB patients rose exponentially from 1.5% to 9.0% during the study period. Young (<35 years), single, male patients were mostly affected; injection drug use was a potent risk factor. After correction for HIV infection, the trend in TB reporting rates changed from a 1.9% increase to a 0.4% decrease per year. An emerging HIV epidemic, concentrated in young, male, injection drug users, is responsible for increased TB reporting rates in urban Vietnam.

Impact of HIV on novel therapies for tuberculosis control

OBJECTIVE AND DESIGN

The increased risk for tuberculosis in HIV-infected people has fueled a worldwide resurgence of tuberculosis. A major hindrance to controlling tuberculosis is the long treatment duration, leading to default, jeopardizing cure, and generating drug resistance. We investigated how tuberculosis is impacted by reducing treatment duration alone or combined with enhanced case detection and/or cure under different HIV prevalence levels.

METHODS

Our model includes HIV stages I-IV and was calibrated to long-term tuberculosis and HIV data from Kenya. Benefits were assessed in terms of absolute and relative reductions in new tuberculosis cases and deaths.

RESULTS

Compared with present-day strategies, at 3-20% HIV prevalence we attain a 6-20% decrease in incidence and mortality in 25 years when reducing treatment duration alone; benefits exceed 300% when combined with increased detection and cure. Benefits vary substantially according to HIV status and prevalence. Challenges arise because in absolute terms the number of infected people and deaths increases dramatically with increasing HIV prevalence, and because the relative efficacy of tuberculosis control policies displays a nonlinear pattern whereby they become less effective on a per capita basis at HIV prevalence levels greater than 15%. Benefits of reducing treatment duration may even be reversed at extreme HIV prevalence levels. Benefits of increasing cure versus detection increase as HIV prevalence increases.

CONCLUSION

Reducing tuberculosis treatment duration, alone or in combination with other control strategies, can provide enormous benefits at high HIV prevalence. Tuberculosis control policies need to account for HIV levels because the efficacy of different interventions varies substantially with HIV prevalence.

Modeling the joint epidemics of TB and HIV in a South African township

We present a simple mathematical model with six compartments for the interaction between HIV and TB epidemics. Using data from a township near Cape Town, South Africa, where the prevalence of HIV is above 20% and where the TB notification rate is close to 2,000 per 100,000 per year, we estimate some of the model parameters and study how various control measures might change the course of these epidemics. Condom promotion, increased TB detection and TB preventive therapy have a clear positive effect. The impact of antiretroviral therapy on the incidence of HIV is unclear and depends on the extent to which it reduces sexual transmission. However, our analysis suggests that it will greatly reduce the TB notification rate.

Controlling Co-Epidemics: Analysis of HIV and Tuberculosis Infection Dynamics

A co-epidemic arises when the spread of one infectious disease stimulates the spread of another infectious disease. Recently, this has happened with human immunodeficiency virus (HIV) and tuberculosis (TB). We develop two variants of a co-epidemic model of two diseases. We calculate the basic reproduction number (R(0)), the disease-free equilibrium, and the quasi-disease-free equilibria, which we define as the existence of one disease along with the complete eradication of the other disease, and the co-infection equilibria for specific conditions. We determine stability criteria for the disease-free and quasi-disease-free equilibria. We present an illustrative numerical analysis of the HIV-TB co-epidemics in India that we use to explore the effects of hypothetical prevention and treatment scenarios. Our numerical analysis demonstrates that exclusively treating HIV or TB may reduce the targeted epidemic, but can subsequently exacerbate the other epidemic. Our analyses suggest that coordinated treatment efforts that include highly active antiretroviral therapy for HIV, latent TB prophylaxis, and active TB treatment may be necessary to slow the HIV-TB co-epidemic. However, treatment alone may not be sufficient to eradicate both diseases. Increased disease prevention efforts (for example, those that promote condom use) may also be needed to extinguish this co-epidemic. Our simple model of two synergistic infectious disease epidemics illustrates the importance of including the effects of each disease on the transmission and progression of the other disease.

Tuberculosis

Tuberculosis is still a leading cause of death in low-income and middle-income countries, especially those of sub-Saharan Africa where tuberculosis is an epidemic because of the increased susceptibility conferred by HIV infection. The effectiveness of the Bacille Calmette Guérin (BCG) vaccine is partial, and that of treatment of latent tuberculosis is unclear in high-incidence settings. The routine diagnostic methods that are used in many parts of the world are still very similar to those used 100 years ago. Multidrug treatment, within the context of structured, directly observed therapy, is a cost-effective control strategy. Nevertheless, the duration of treatment needed reduces its effectiveness, as does the emergence of multidrug-resistant and extensively drug-resistant disease; the latter has recently become widespread. The rapid expansion of basic, clinical, and operational research, in addition to increasing knowledge of tuberculosis, is providing new diagnostic, treatment, and preventive measures. The challenge is to apply these advances to the populations most at risk. The development of a comprehensive worldwide plan to stop tuberculosis might facilitate this process by coordinating the work of health agencies. However, massive effort, political will, and resources are needed for this plan to succeed.

Quantitative impact of human immunodeficiency virus infection on tuberculosis dynamics

RATIONALE

Human immunodeficiency virus (HIV) infection has a major but unquantified impact on the risk of tuberculosis.

OBJECTIVES

To quantify the impact of HIV infection on the number of tuberculosis cases in San Francisco.

METHODS

We studied all patients reported with tuberculosis in San Francisco from 1991 to 2002. The initial isolates of Mycobacterium tuberculosis were genotyped using IS6110 restriction fragment-length polymorphism genotyping as the primary method, and clustered cases (identical genotype patterns) were identified.

MEASUREMENTS AND MAIN RESULTS

We determined the case number, case rate, and the fraction of tuberculosis attributable to HIV infection. Of 2,991 reported tuberculosis cases, 2,193 (73.3%) had a genotype pattern of M. tuberculosis available. Genotypic clusters with at least one HIV-positive person were larger, lasted longer, and had a shorter time between successive cases relative to clusters with only HIV-uninfected persons (P < 0.00005, P = 0.0009, P = 0.018, respectively). Overall, 13.7% of the tuberculosis cases were attributable to HIV infection and an estimated 405 excess tuberculosis cases occurred.

CONCLUSIONS

During a period encompassing the resurgence and decline of tuberculosis in San Francisco, a substantial number of the tuberculosis cases were attributable to HIV infection. Coinfection with HIV amplified the local tuberculosis epidemic.

Facilitating interaction between TB and AIDS medical services for better management of patients with co-infections

The Newly Independent States inherited two vertical services for tuberculosis (TB) and AIDS control from the Soviet Union. TB is an important cause of morbidity in the Central Asia Region (CAR). In recent years, HIV epidemics started growing rapidly, especially among injection drug users. TB is the most common AIDS-related opportunistic infection, leading to early deaths among AIDS patients and increased transmission of TB in the general population. An assessment carried out between March 2005 and May 2005 revealed that TB and AIDS services in CAR rarely interacted for the management of patients with co-infections. Following the assessment, the USAID-funded CAPACITY Project promoted cooperation between TB and AIDS services in Uzbekistan, Tajikistan, and Kyrgyzstan. For the first time, representatives from the Ministries of Health and Justice, national and regional TB and AIDS centres, international organizations, and local non-governmental organizations (NGO) gathered to discuss mechanisms for linking TB and AIDS services to address the growing needs of co-infected patients. Technical Working Groups (TWG) established through this cooperation developed linkages between TB and AIDS services. These groups developed protocols, guidelines, and training programmes. Hundreds of medical specialists, health managers, and monitoring and evaluation specialists were trained and national teams of trainers were built. TB/HIV model sites were designed in each country and the models were implemented to test and refine the approaches for patients with co-infections. Key to the success of the approach has been the emphasis on wide participation from all stakeholders. Upon completion, successful models will be advocated for funding and national scale-up.

A case for passive immunoprophylaxis against tuberculosis

HIV-associated tuberculosis is escalating ominously in Africa and southeast Asia despite existing control measures. Therefore, new approaches to tuberculosis control need to be explored. We discuss the potential use of passive immunoprophylaxis with antibodies in tuberculosis control. Although the predominant type of active host resistance is T-cell mediated, recent results in mouse experimental models suggest that monoclonal antibodies to certain antigens (eg, Acr or lipoarabinomannan) can impart substantial passive protection against tuberculous infection. These results are corroborated by data from other laboratories on passive vaccination against a number of intracellular microbial pathogens. Further work is needed to develop human (or humanised) antibody reagents, to increase their protective efficacy, and to expand our understanding of the mechanisms of antibody action.

Beneficial and perverse effects of isoniazid preventive therapy for latent tuberculosis infection in HIV-tuberculosis coinfected populations

In sub-Saharan Africa, where the emergence of HIV has caused dramatic increases in tuberculosis (TB) case notifications, new strategies for TB control are necessary. Isoniazid preventive therapy (IPT) for HIV-TB coinfected individuals reduces the reactivation of latent Mycobacterium tuberculosis infections and is being evaluated as a potential community-wide strategy for improving TB control. We developed a mathematical model of TB/HIV coepidemics to examine the impact of community-wide implementation of IPT for TB-HIV coinfected individuals on the dynamics of drug-sensitive and -resistant TB epidemics. We found that community-wide IPT will reduce the incidence of TB in the short-term but may also speed the emergence of drug-resistant TB. We conclude that community-wide IPT in areas of emerging HIV and drug-resistant TB should be coupled with diagnostic and treatment policies designed to identify and effectively treat the increasing proportion of patients with drug-resistant TB.

The potential impact of enhanced diagnostic techniques for tuberculosis driven by HIV: a mathematical model

OBJECTIVE

To explore the potential impact of enhanced tuberculosis (TB) diagnostic techniques as a TB control strategy in an adult population with high HIV prevalence.

DESIGN

A compartmental difference-equation model of TB/HIV was developed using parameter estimates from the literature.

METHODS

The impact of five TB control interventions (rapid molecular testing, mycobacterial culture, community-wide and HIV-targeted active case finding, and highly active antiretroviral therapy) on TB incidence, prevalence, and mortality was modeled in a steady-state population with an HIV prevalence of 17% and annual TB incidence of 409 per 100 000. Sensitivity analyses assessed the influence of each model parameter on the interventions' mortality impact.

RESULTS

Enhanced diagnostic techniques (rapid molecular testing or culture) are each projected to reduce TB prevalence and mortality by 20% or more, an impact similar to that of active case-finding in 33% of the general community and greater than the effect achievable by case-finding or antiretroviral treatment efforts in HIV-positive patients alone. The projected impact of enhanced diagnostics on TB incidence (< 10% reduction) is smaller. The impact of TB diagnostics is sensitive to the quality of existing diagnostic standards and the level of access to diagnostic services, but is robust across a wide range of population parameters including HIV and TB incidence.

CONCLUSIONS

Enhanced TB diagnostic techniques may have substantial impact on TB morbidity and mortality in HIV-endemic regions. As TB rates continue to increase in these areas, enhanced diagnostic techniques merit further consideration as TB control strategies.

Tuberculosis in sub-Saharan Africa: opportunities, challenges, and change in the era of antiretroviral treatment

Rapid scale-up of antiretroviral treatment programmes is happening in Africa, driven by international advocacy and policy directives and supported by unprecedented donor funding and technical assistance. This welcome development offers hope to millions of HIV-infected Africans, among whom tuberculosis is the major cause of serious illness and death. Little in the way of HIV diagnosis or care was previously offered to patients with tuberculosis, by either national tuberculosis or AIDS control programmes, with tuberculosis services focused exclusively on diagnosis and treatment of rising numbers of patients. Tuberculosis control in Africa has yet to adapt to the new climate of antiretroviral availability. Many barriers exist, from drug interactions to historic differences in the way that tuberculosis and HIV are perceived, but failure to successfully integrate HIV and tuberculosis control will threaten the viability of both programmes. Here, we review tuberculosis epidemiology in Africa and policy implications of HIV/AIDS treatment scale-up.

Cardiovascular disease and toxicities related to HIV infection and its therapies

Cardiovascular manifestations of HIV vary according to disease stage, treatment regimen and geographical location. Common cardiac complications of HIV disease in patients off highly active antiretroviral therapy (HAART) include dilated cardiomyopathy, myocarditis, pericardial effusion, endocarditis, pulmonary hypertension and non-antiretroviral drug-related cardiotoxicity. However, with the introduction of HAART that has substantially modified the course of HIV disease by lengthening survival, additional cardiovascular consequences are a result of the metabolic syndrome with a propensity toward hyperlipidaemia and atherosclerotic heart disease. Because most of the world's HIV-infected patients have not been treated with HAART, the principal HIV-associated cardiovascular manifestations of patients off HAART are reviewed and new knowledge about the prevalence, pathogenesis and treatment in the HAART era are emphasised in this review. Exercise, a nonpharmacological approach to treating HAART-associated metabolic syndrome, is also discussed.

Synthesis and in vitro and in vivo antimycobacterial activity of isonicotinoyl hydrazones

The purpose of this study was to prepare various isoniazid derivatives by introducing the isoniazid pharmacophore into several molecules and screening for antimycobacterial activity. Ortho-hydroxy acetophenone reacts with isoniazid to form acid hydrazones. The C-Mannich bases of the above acid hydrazones were prepared by reacting them with formaldehyde and various secondary amines. The synthesized compounds were screened against M. tuberculosis H(37)R(v) using the alamar blue susceptibility test. The synthesized compounds inhibit Mycobacterium tuberculosis strain H(37)R(v) with minimum inhibitory concentrations ranging from 0.56 to 4.61 microM. Compound N'-{1-[2-hydroxy-3-(piperazin-1-ylmethyl)phenyl]ethylidene}isonicotinohydrazide 8 was found to be the most active compound with an MIC of 0.56 microM, and was more potent than isoniazid (MIC of 2.04 microM). After 10 days of treatment, compound 8 decreased the bacterial load in murine lung tissue by 3.7-log10 as compared to controls, which was equipotent to isoniazid. The results demonstrate the potential and importance of developing new isoniazid derivatives against mycobacterial infections.

Cost, affordability and cost-effectiveness of strategies to control tuberculosis in countries with high HIV prevalence

BACKGROUND

The HIV epidemic has caused a dramatic increase in tuberculosis (TB) in East and southern Africa. Several strategies have the potential to reduce the burden of TB in high HIV prevalence settings, and cost and cost-effectiveness analyses can help to prioritize them when budget constraints exist. However, published cost and cost-effectiveness studies are limited.

METHODS

Our objective was to compare the cost, affordability and cost-effectiveness of seven strategies for reducing the burden of TB in countries with high HIV prevalence. A compartmental difference equation model of TB and HIV and recent cost data were used to assess the costs (year 2003 USD prices) and effects (TB cases averted, deaths averted, DALYs gained) of these strategies in Kenya during the period 2004-2023.

RESULTS

The three lowest cost and most cost-effective strategies were improving TB cure rates, improving TB case detection rates, and improving both together. The incremental cost of combined improvements to case detection and cure was below USD 15 million per year (7.5% of year 2000 government health expenditure); the mean cost per DALY gained of these three strategies ranged from USD 18 to USD 34. Antiretroviral therapy (ART) had the highest incremental costs, which by 2007 could be as large as total government health expenditures in year 2000. ART could also gain more DALYs than the other strategies, at a cost per DALY gained of around USD 260 to USD 530. Both the costs and effects of treatment for latent tuberculosis infection (TLTI) for HIV+ individuals were low; the cost per DALY gained ranged from about USD 85 to USD 370. Averting one HIV infection for less than USD 250 would be as cost-effective as improving TB case detection and cure rates to WHO target levels.

CONCLUSION

To reduce the burden of TB in high HIV prevalence settings, the immediate goal should be to increase TB case detection rates and, to the extent possible, improve TB cure rates, preferably in combination. Realising the full potential of ART will require substantial new funding and strengthening of health system capacity so that increased funding can be used effectively.

Tuberculosis control in the era of HIV

Without HIV, the tuberculosis (TB) epidemic would now be in decline almost everywhere. However, instead of looking forward to the demise of TB, countries that are badly affected by HIV are struggling against a rising tide of HIV-infected patients with TB. As a consequence, global TB control policies have had to be revised and control of TB now demands increased investment. This paper assesses what is being done to address the issue and what remains to be done.

Tuberculosis and HIV interaction in sub-Saharan Africa: impact on patients and programmes; implications for policies

Sub-Saharan Africa carries the overwhelming share of the global burden of human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) and of HIV-associated tuberculosis (TB). The impact of HIV on TB patients and programmes has implications for TB control policies. The impact on patients includes the effect of HIV on diagnosis and on the patterns of HIV-related TB, the response of HIV-infected TB patients to TB treatment, the benefits of antiretroviral therapy (ART), and the quality and continuity of care for TB patients. The impact on national TB programmes (NTPs) includes increased case load, impaired NTP performance, increased need for access to ART and difficulties in reaching TB control targets. Implications for policies include the need to promote TB and HIV/AIDS programme collaboration, aimed at improving NTP performance (TB case-finding and treatment outcomes), quality and continuity of care, and monitoring and interpretation of progress towards TB control targets. In order to provide the recommended international standard of care for TB patients, clinicians need to be aware of the impact of HIV on TB patients and programmes and the implications for the policies that provide the framework for this standard. Conversely, policy-makers need to understand the impact of HIV on TB patients and programmes. This can help to ensure a firm evidence base for TB control policies aiming at the high standard of patient care that is at the heart of TB and HIV programmes.

How effectively does HAART restore immune responses to Mycobacterium tuberculosis? Implications for tuberculosis control

Use of highly active antiretroviral treatment (HAART) has had a major impact on HIV-associated morbidity and mortality in industrialized countries. Access to HAART is now expanding in low-income countries where tuberculosis (TB) is the most important opportunistic disease. The incidence of TB has been fueled by the HIV epidemic and in many countries with high HIV prevalence current TB control measures are failing. HAART reduces the incidence of TB in treated cohorts by approximately 80% and therefore potentially has an important role in TB control in such countries. However, despite the huge beneficial effect of HAART, rates of TB among treated patients nevertheless remain persistently higher than among HIV-negative individuals. This observation raises the important question as to whether immune responses to Mycobacterium tuberculosis (MTB) are completely or only partially restored during HAART. Current data suggest that full restoration of circulating CD4 cell numbers occurs only among a minority of patients and that, even among these, phenotypic abnormalities and functional defects in lymphocyte subsets often persist. Suboptimal restoration of MTB-specific immune responses may greatly reduce the extent to which HAART is able to contribute to TB control at the community level because patients receiving HAART live much longer and yet would maintain a chronically heightened risk of TB.

The impact of HIV/AIDS on the control of tuberculosis in India

Epidemics of HIV/AIDS have increased the tuberculosis (TB) case-load by five or more times in East Africa and southern Africa. As HIV continues to spread, warnings have been issued of disastrous AIDS and TB epidemics in "new-wave" countries, including India, which accounts for 20% of all new TB cases arising in the world each year. Here we investigate whether, in the face of the HIV epidemic, India's Revised National TB Control Program (RNTCP) could halve TB prevalence and death rates in the period 1990-2015, as specified by the United Nations Millennium Development Goals. Using a mathematical model to capture the spatial and temporal variation in TB and HIV in India, we predict that, without the RNTCP, HIV would increase TB prevalence (by 1%), incidence (by 12%), and mortality rates (by 33%) between 1990 and 2015. With the RNTCP, however, we expect substantial reductions in prevalence (by 68%), incidence (by 41%), and mortality (by 39%) between 1990 and 2015. In India, 29% of adults but 72% of HIV-positive adults live in four large states in the south where, even with the RNTCP, mortality is expected to fall by only 15% between 1990 and 2015. Nationally, the RNTCP should be able to reverse the increases in TB burden due to HIV but, to ensure that TB mortality is reduced by 50% or more by 2015, HIV-infected TB patients should be provided with antiretroviral therapy in addition to the recommended treatment for TB.

A new vaccine against tuberculosis shows greater protection in a mouse model with progressive pulmonary tuberculosis

SETTING

The effectiveness of Bacillus Calmette-Guerin (BCG) vaccination in reducing tuberculosis (TB) prevalence rates is poor, resulting in urgent need for improved immunization programs, with new and more effective vaccines against TB.

OBJECTIVE

To develop a recombinant Tice BCG vaccine against TB that overexpresses the 38-kDa antigen of Mycobacterium tuberculosis in order to protect against infection by M. tuberculosis H37Rv and hyper-virulent M. tuberculosis Beijing genotype.

DESIGN

M. tuberculosis 38-kDa protein was cloned into a mycobacterial shuttle plasmid, which was used to overexpress the 38 kDa protein in BCG Tice to produce the recombinant vaccine, rBCG38 Tice (rBCG38).

RESULTS

Compared with BCG Tice, which conferred little protection against the Beijing strain of M. tuberculosis, vaccination with the rBCG38 increased survival of mice infected with either M. tuberculosis H37Rv or a Beijing strain of M. tuberculosis, isolate 9501000. Vaccination with either BCG Tice or rBCG38 resulted in enhanced protection against mycobacterial growth in lung tissue by reducing the number of colony-forming units (CFU). The vaccine induced a strong and highly significant Th1 response, shown by the high level of IL-2 and IFN-gamma cytokine producer cells found in the lungs of challenged mice, and an increase in the IgG2a:IgG1 ratio found in the pooled sera of the vaccinated mice.

CONCLUSIONS

This study showed that rBCG38 vaccine induced a strong Th1 response, demonstrated by the high levels of IL-2 and IFN-gamma producer cells and IgG2a. Protection was mediated for as long as 6 and 4 months after challenge with M. tuberculosis H37Rv and Beijing genotypes, respectively.