Force of tuberculosis infection among adolescents in a high HIV and TB prevalence community: a cross-sectional observation study

BACKGROUND: Understanding of the transmission dynamics of tuberculosis (TB) in high TB and HIV prevalent settings is required in order to develop effective intervention strategies for TB control. However, there are little data assessing incidence of TB infection in adolescents in these settings. METHODS: We performed a tuberculin skin test (TST) and HIV survey among secondary school learners in a high HIV and TB prevalence community. TST responses to purified protein derivative RT23 were read after 3 days. HIV-infection was assessed using Orasure(R) collection device and ELISA testing. The results of the HIV-uninfected participants were combined with those from previous surveys among primary school learners in the same community, and force of TB infection was calculated by age. RESULTS: The age of 820 secondary school participants ranged from 13 to 22 years. 159 participants had participated in the primary school surveys. At a 10 mm cut-off, prevalence of TB infection among HIV-uninfected and first time participants, was 54% (n = 334/620). HIV prevalence was 5% (n = 40/816). HIV infection was not significantly associated with TST positivity (p = 0.07). In the combined survey dataset, TB prevalence was 45% (n = 645/1451), and was associated with increasing age and male gender. Force of infection increased with age, from 3% to 7.3% in adolescents [greater than or equal to]20 years of age. CONCLUSIONS: We show a high force of infection among adolescents, positively associated with increasing age. We postulate this is due to increased social contact with infectious TB cases. Control of the TB epidemic in this setting will require reducing the force of infection

Comparison of two active case-finding strategies for community-based diagnosis of symptomatic smear-positive tuberculosis and control of infectious tuberculosis in Harare, Zimbabwe (DETECTB): a cluster-randomised trial

BACKGROUND: Control of tuberculosis in settings with high HIV prevalence is a pressing public health priority. We tested two active case-finding strategies to target long periods of infectiousness before diagnosis, which is typical of HIV-negative tuberculosis and is a key driver of transmission. METHODS: Clusters of neighbourhoods in the high-density residential suburbs of Harare, Zimbabwe, were randomised to receive six rounds of active case finding at 6-monthly intervals by either mobile van or door-to-door visits. Randomisation was done by selection of discs of two colours from an opaque bag, with one disc to represent every cluster, and one colour allocated to each intervention group before selection began. In both groups, adult (≥16 years) residents volunteering chronic cough (≥2 weeks) had two sputum specimens collected for fluorescence microscopy. Community health workers and cluster residents were not masked to intervention allocation, but investigators and laboratory staff were masked to allocation until final analysis. The primary outcome was the cumulative yield of smear-positive tuberculosis per 1000 adult residents, compared between intervention groups; analysis was by intention to treat. The secondary outcome was change in prevalence of culture-positive tuberculosis from before intervention to before round six of intervention in 12% of randomly selected households from the two intervention groups combined; analysis was based on participants who provided sputum in the two prevalence surveys. This trial is registered, number ISRCTN84352452. FINDINGS: 46 study clusters were identified and randomly allocated equally between intervention groups, with 55 741 adults in the mobile van group and 54,691 in the door-to-door group at baseline. HIV prevalence was 21% (1916/9060) and in the 6 months before intervention the smear-positive case notification rate was 2·8 per 1000 adults per year. The trial was completed as planned with no adverse events. The mobile van detected 255 smear-positive patients from 5466 participants submitting sputum compared with 137 of 4711 participants identified through door-to-door visits (adjusted risk ratio 1·48, 95% CI 1·11-1·96, p=0·0087). The overall prevalence of culture-positive tuberculosis declined from 6·5 per 1000 adults (95% CI 5·1-8·3) to 3·7 per 1000 adults (2·6-5·0; adjusted risk ratio 0·59, 95% CI 0·40-0·89, p=0·0112). INTERPRETATION: Wide implementation of active case finding, particularly with a mobile van approach, could have rapid effects on tuberculosis transmission and disease. FUNDING: Wellcome Trust

Yield of HIV-associated tuberculosis during intensified case finding in resource-limited settings: a systematic review and meta-analysis

Intensified case finding is the regular screening for evidence of tuberculosis in people infected with HIV, at high risk of HIV, or living in congregate settings. We systematically reviewed studies of intensified case finding published between January, 1994, and April, 2009. In 78 eligible studies, the number of people with tuberculosis detected during intensified case finding varied substantially between countries and target groups of patients. Median prevalence of newly diagnosed tuberculosis was 0·7% in population-based surveys, 2·2% in contact-tracing studies, 2·3% in mines, 2·3% in programmes preventing mother-to-child transmission of HIV, 2·5% in prisons, 8·2% in medical and antiretroviral treatment clinics, and 8·5% in voluntary counselling and testing services. Metaregression analysis of studies that included only people with HIV showed that for each increment in national prevalence of tuberculosis of 100 cases per 100 000 population, intensified case finding identified an additional one case per 100 screened individuals (p=0·03). Microbiological sputum examination of all individuals without prior selection by symptom screening yielded an additional four cases per 100 individuals screened (p=0·05). Data on the use of serial screening, treatment outcomes in actively identified cases of tuberculosis, and cost-effectiveness, however, were lacking. Concerted action is needed to develop intensified case finding as an important method for control of tuberculosis