Tuberculosis infection and disease in people living with HIV in countries with low tuberculosis incidence.

In countries with low tuberculosis (TB) incidence, TB is concentrated in vulnerable populations, including people living with the human immunodeficiency virus (PLHIV), who have a substantially greater risk of TB than people without HIV. We searched PubMed, EMBASE and Web of Science for studies evaluating the risk factors for latent tuberculous infection (LTBI) or active TB in PLHIV in countries with TB incidence 10 per 100 000 population. Due to the number of risk factors evaluated and heterogeneity in study designs, we present summary data and a narrative synthesis. We included 45 studies: 17 reported data on the risk factors for LTBI and 32 on active TB. Black, Asian or Hispanic ethnicity, birth or long-term residence in a country with high TB incidence, and HIV acquisition via injecting drug use (IDU) or heterosexual sex were strong predictors of both LTBI and active TB. History of contact, a greater degree of immunosuppression at diagnosis or higher viral load increased the TB risk. Early HIV diagnosis to allow timely initiation of antiretroviral therapy is essential for the prevention of TB in PLHIV. Screening and treating PLHIV for LTBI to reduce the risk of progression to active TB disease should also be considered to further reduce the burden of active TB in low TB incidence settings. Research to support the expansion of TB and HIV prevention and treatment globally is essential to eliminate TB in low-incidence settings.

Isoniazid-resistant tuberculosis: a cause for concern?

The drug isoniazid (INH) is a key component of global tuberculosis (TB) control programmes. It is estimated, however, that 16.1% of TB disease cases in the former Soviet Union countries and 7.5% of cases outside of these settings have non-multidrug-resistant (MDR) INH resistance. Resistance has been linked to poorer treatment outcomes, post-treatment relapse and death, at least for specific sites of disease. Multiple genetic loci are associated with phenotypic resistance; however, the relationship between genotype and phenotype is complex, and restricts the use of rapid sequencing techniques as part of the diagnostic process to determine the most appropriate treatment regimens for patients. The burden of resistance also influences the usefulness of INH preventive therapy. Despite seven decades of INH use, our knowledge in key areas such as the epidemiology of resistant strains, their clinical consequences, whether tailored treatment regimens are required and the role of INH resistance in fuelling the MDR-TB epidemic is limited. The importance of non-MDR INH resistance needs to be re-evaluated both globally and by national TB control programmes.

Active case finding for tuberculosis among high-risk groups in low-incidence countries.

In low-incidence countries, tuberculosis (TB) is now largely concentrated in high-risk groups such as migrants, homeless people, illicit drug users, alcoholics and prisoners. This has led to increased efforts to implement targeted active case finding for TB among specific populations. This review examines the evidence supporting active case finding in migrants and social risk groups, as well as the cost-effectiveness of interventions. While data from observational studies support active case finding in defined high-risk groups, further research to determine the effectiveness of specific tools and the cost-effectiveness of screening strategies is needed to inform evidence-based control methods in low-incidence countries. Inevitably, addressing TB in low-incidence countries will depend on effective disease control in high-burden countries.

Active case finding for pulmonary tuberculosis using mobile digital chest radiography: an observational study.

BACKGROUND: Mobile digital chest radiography (CXR) is used routinely to screen for pulmonary tuberculosis (PTB) in London among homeless populations, persons accessing drug treatment services and prisoners. OBJECTIVE: 1) To establish the sensitivity and specificity of mobile digital CXR, and 2) to test the hypothesis that actively identified cases have reduced odds of sputum smear positivity vs. those presenting passively to health care services from the same populations. METHODS: Sensitivity and specificity were calculated using a gold standard comparator of culture-confirmed cases of PTB reported to the national surveillance system within 90 days of screening. Logistic regression was used to determine whether actively detected cases had reduced odds of smear positivity compared to passively detected cases after adjustment for confounding. RESULTS: The intervention had a sensitivity of 81.8% (95%CI 64.5-93.0) and a specificity of 99.2% (95%CI 99.1-99.3). After adjusting for confounding, there was evidence that cases identified through screening were less likely to be smear-positive than passively identified cases (OR 0.34, 95%CI 0.14-0.85; likelihood ratio test P = 0.022). CONCLUSION: Digital CXR achieves a high level of sensitivity and specificity in an operational setting; targeted mobile radiographic screening can reduce the risk of onward transmission by identifying cases before they become infectious.