BCG vaccine. Its efficacy and impact on the results of tuberculin screening in a high-risk population.

Abstract

In a housing estate population with a high prevalence of tuberculosis, the authors conducted tuberculosis screening with the tuberculin test, and an investigation with three purposes: evaluation of tuberculosis infection (defined as > 10 mm on tuberculin test), evaluation of BCG effect on tuberculin test, and evaluation of BCG efficacy. The data was collected by nurses during the screening and completed with observation of vaccination records in a health center. The diagnosis of tuberculosis was done by local specialized health services. The statistical significance was tested with Chi Square and Fisher Tests. Vaccine efficacy was calculated on the basis of relative risk of contracting tuberculosis according to vaccination status. The authors tested tuberculin reactivity on 396 persons -53.5% of whole population resident in the neighbourhood. The infection was more prevalent in the 15-44-years-old group (31.2%), in males (25.9%) and black population (30.5%). Only the differences between age groups were statistically significant. After the discussion of probable bias, the authors conclude that BCG does not convert the tuberculin test significantly when the cutpoint is of 10 mm, in a high prevalent tuberculosis population. Therefore, the tuberculin test could be a good diagnostic test for infection, even in vaccinated groups. Lastly, the vaccine efficacy was not confirmed, probably because of the small magnitude of sample size.