High prevalence and risk factors associated with latent tuberculous infection in two Colombian prisons

Setting: Two prisons in Medellín and Itagüí, Colombia.

Objective: To determine the prevalence of tuberculin skin test (TST) positivity in prisoners and the annual risk of tuberculous infection (ARTI), to identify risk factors associated with a positive result, and to describe progression to active disease.

Design: Cross-sectional study. Inmates were included if time of incarceration was 71 year and excluded if subjects had had previous or active tuberculosis (TB), or conditions that could hamper TST administration or interpretation.

Results: We screened 1014 inmates. The overall prevalence of TST positivity was 77.6%. The first TST administration resulted in 66% positivity, and the second TST an additional 11.6%. In Prison One, the ARTI was 5.09% in high TB incidence cell blocks and 2.72% in low TB incidence blocks. In Prison Two, the ARTI was 2.77%. Risk factors associated with TST positivity were history of previous incarceration and length of incarceration. Among all those included in the study, four individuals developed active pulmonary TB.

Conclusion: Prevalence of TST positivity in prisoners and the ARTI were higher than in the general population, but differed between prisons; it is important to apply a second TST to avoid an overestimation of converters during follow-up.