Prevalence of Latent TB and effectiveness of BCG vaccination against Latent Tuberculosis. An Observational Study.

Abstract

OBJECTIVES\nThe aims of the present study were to determine the prevalence of LTBI in immigrant children and adolescents (0-17 years) living in or recently coming to Sweden and to estimate the effectiveness of BCG against latent TB (LTBI) in immigrant children coming to Sweden from high-incidence countries, most of them asylum seekers. LTBI was defined as positive Quantiferon or in small children from whom it was difficult to get 3 mL of blood as a tuberculin skin test (TST) of ≥ 10 mm.\n\n\nDESIGN\nAs a substitute for written documentation of BCG vaccination a typical BCG scar was used. The study comprised 1,404 immigrants aged 0-17 years. The arms and legs of all of them were inspected for a BCG scar and Quantiferon or TST was performed. The study was a retrospective, observational, comparative cohort study.\n\n\nRESULTS\nLTBI was found in 123 of 1011 (12%) children with a BCG scar and in 116 of 393 (29.5 %) without a BCG scar giving an estimated vaccine effectiveness of 59 %.\n\n\nCONCLUSIONS\nLTBI is common among immigrant children (17 %). LTBI can progress to active TB and will then spread in the immigrant population and to the general population if all arrivals are not tested and given prophylactic treatment if they have LTBI. The BCG vaccine has a significant effect on LTBI (59 %).