Abstract:

Objective To understand the prevalence of latent tuberculosis infection (LTBI) among TB contacts who were institutionalized for drugs in a compulsory rehabilitation center; further, to analyze the factors associated with risks of TB infection.Methods Five TB cases were detected during October to November, 2016. Tuberculosis skin test (TST) for TB infection were provided to all the institutionalized persons who had contacted the TB cases at the same period. Follow-up TSTs were given every 6 months to these contacts for two years. TST positivity is defined as an induration ≥10 mm for BCG-vaccinated (with a BCG scar), or ≥5 mm for people without a BCG scar, according to the WS 288-2017 Diagnosis for pulmonary tuberculosis. Prevalence of LTBI were measured, and logistic regression was applied for analyzing the factors associated with LTBI.Results Of the 792 TB contacts, 25 declined the TST. The prevalence of LTBI at the first TST examination was 57.9% (444 among the 767 contacts). During the follow-up, another 54 contacts who were negative at first became TST positive, led to an 16.7% (54/323) increment. In total, the 2-year positivity was 64.9% (498/767). Of the 498 TST positive cases, 54 had a diminished TST induration, which suggested a change to TST negative (10.8%, 54/498). Age (Wald χ ²=10.942,P=0.001,OR=1.04, 95%CI: 1.02-1.06), BCG vaccination (Wald χ ²=4.533,P=0.033,OR=1.41, 95%CI 1.03-1.93) and close contact to TB patients (Wald χ ²=6.343,P=0.012,OR=1.68, 95%CI: 1.12-2.52) were significantly associated with LTBI by TST in the study population. Conclusion The prevalence of LTBI is high among the institutionalized persons in the compulsory rehabilitation center. About one-sixth of non-infected by TST at the first testing could become LTBI positive while one of ten might change the LTBI status from positive to negative during a two-year period. Increased age, history of BCG vaccination and close contacts with TB patients had an increased possibility of TB infection by TST.

Key words: Tuberculosis,pulmonary, Contact tracing, Tuberculin test, Infection, Population surveillance, Factor analysis,statistical, Drug user