Prevalence and incidence rates of latent tuberculous infection in a large prison in Iran

BACKGROUND: Prisons can act as reservoirs of tuberculous infection. Previous studies have shown that the prevalence of latent tuberculous infection (LTBI) is high in prisons. OBJECTIVE: To investigate the prevalence and incidence rates of LTBI and contributing factors in a prison population in Iran. METHODS: In March 2013, inmates at the Hamadan Central Prison were invited to participate in a voluntary two-stage screening programme using the tuberculin skin test (TST). In the first stage, the standard TST was administered and read, and was repeated in negative cases to identify cases with delayed TST reactivity and boosted reaction. In the second stage, inmates with a SUMMARY true-negative TST underwent repeat screening 6 months later to identify incident LTBI. Information about risk factors was obtained using structured interviews. RESULTS: Among 1208 screened inmates, TST positivity was recorded in 756 cases (prevalence 62.6%). HIV positive inmates and cigarette smokers were also more likely to have LTBI. In 380 inmates returning for a follow-up visit, the 6-month incidence rate was 7.6%. Two cases of pulmonary tuberculosis were identified during the period of study. CONCLUSIONS: LTBI prevalence and incidence rates among Iranian prisoners are high. Comprehensive plans are needed to for effective TB control among prisoners.