Current tuberculin reactivity of schoolchildren in the Central African Republic

Background: The tuberculin skin test (TST) is the recommended method for screening for Mycobacterium tuberculosis infection in many countries. We used this technique to assess bacillus Calmette-Guerin (BCG) status and to estimate the current prevalence and annual rate of latent tuberculosis infection in schoolchildren in the Central African Republic. Methods: Two tuberculin units of 0.1 ml purified protein derivative TR23 were injected intradermally into the left forearm of 2710 children attending school in Bangui and Ombella M'Poko. The induration size was interpreted at cut-off points of >= 5 mm, >= 10 mm and >= 15 mm. The annual infection rate was estimated as the average number of infections in the study sample each year between birth and the time of the survey. Results: Overall, there was no reaction to the TST (no induration) in 71.7 % (95 CI, 68.3-75.3 %) of BCG-vaccinated children and 82.9 % (95 CI, 74.1-91.4 %) of non-vaccinated children. The proportions of children who gave a TST reaction above >= 10 mm and >= 15 mm cut-off was 18.4 % (95 % CI, 16.8-20.1 %) and 8.9 % (95 % CI, 7.8-10.0 %), respectively. The proportions of TST reaction above these cut-offs were 19.6 % (95 % CI, 17.4-21.9 %) and 8.1 % (95 % CI, 6.7-9.6 %), respectively. The annual infection rate was 0.8 % at the cut-off point of >= 15 mm. Conclusion: This study provides updated data on rates of tuberculosis infection in the Central African Republic. It is remarkable that most of the children had negative tuberculin reactivity. More studies are required to understand the factors that determine the low tuberculin reactivity in this population.