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 established in 1979 based on the principles currently known as the World Health Organization DOTS strategy. From the period 1983-1987 to 1994-1998, notification 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 infection and to establish to what extent the opposing forces of improved tuberculosis control and HIV have had an impact on tuberculosis transmission.

METHODS

Three national surveys were conducted in Tanzania among primary school children at 5-year intervals. The annual risk of tuberculosis infection and its trend were determined by tuberculin skin testing.

RESULTS

The annual risk of infection in children without BCG scar using the criterion '17 mm + 2 x 18 mm' or more was estimated at 1.1% in 1983-1987, 1.0 in 1988-1992, 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. The 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 infection in children appears to have been stable over the past 15 years in Tanzania. This remarkable achievement is probably due to the impact of the NTP on tuberculosis transmission.