Risk of infection and estimated incidence of tuberculosis in Northern Uganda

The main goals of our study were to evaluate: 1) the annual risk of tuberculosis infection (ARTI) and its annual decrease in Uganda; 2) the expected incidence of new tuberculosis cases and the notification rate; and 3) the role of incentives given to children tested in increasing compliance with the survey procedures. The methodology is based on performing the standard World Health Organization (WHO) tuberculin test on children of the same age groups at intervals of 10-15 yrs, identifying infected persons by induration distribution analysis, and converting the prevalence rates detected into risk rates according to the ARTI model. Two thousand six hundred and twenty one school children aged 10 yrs old and bacilli Calmette-Guerin (BCG) nonvaccinated, in six study areas, were injected with two tuberculin units (TU) of purified protein derivative (PPD) RT 23 Copenhagen. The detected prevalence was 14±1.4% (prevalence +95% confidence interval (95% CI)) and the ARTI value 1.2±0.9%, with an estimated annual decrease of 0.83% from 1958 to 1970 and 2.9% in the 1970-1987 period. The estimated expected incidence of new cases in Uganda was 59 smear positive and 75 smear negative/extrapulmonary cases per 100,000 population in 1987, and 53 and 65, respectively, in 1990, with an overall 68 % notification coverage. No significant improvement in children returning for reading was observed in the group receiving incentives. We conclude that the average decrease (2.9%) probably represents the natural decline of tuberculosis in Uganda. The coverage appears encouraging, although the ARTI detected could be underestimated, since the existing ARTI model was developed and validated before the human immunodeficiency virus (ARTI) era. The importance of implementing adequate surveillance measures needs to be stressed.