Tuberculosis control in the era of the HIV epidemic: risk of tuberculosis infection in Tanzania, 1983-1998

SETTING: In Tanzania, a national tuberculosis programme (NTP) was establish ed in 1979 based on the principles currently known as the world Health Orga nization DOTS strategy. From the period 1983-1987 to 1994-1998, notificatio n rates of smear-positive tuberculosis increased from 32 to 69 per 100 000 population, mainly due to the human immunodeficiency virus (HIV) epidemic. OBJECTIVES: To estimate the trend in the annual risk of tuberculosis infect ion and to establish to what extent the opposing forces of improved tubercu losis control and HIV have had an impact on tuberculosis transmission. METHODS: Three national surveys were conducted in Tanzania among primary sc hool children at 5-year intervals. The annual risk of tuberculosis infectio n and its trend were determined by tuberculin skin testing. RESULTS: The annual risk of infection in children without BCG scar using th e criterion '17 mm + 2 x 18 mm' or more was estimated at 1.1% in 1983-1987, 1.0 in 1988-1332, and 0.9% in 1993-1998. There appears to have been little change in the annual risk of infection over the study period, either when using other criteria to define infection or in children with a BCG scar. Th e estimated number of infections per notified case decreased over time from 36 to 19. CONCLUSIONS: Despite strongly increased tuberculosis notification rates in adults, associated with the HIV epidemic, the risk of tuberculosis infectio n in children appears to have been stable over the past 15 years in Tanzani a. This remarkable achievement is probably due to the impact of the NTP on tuberculosis transmission.