An epidemiological study of tuberculosis and HIV infection in Tanzania, 1991-1993

In Tanzania during the past 6 years reported tuberculosis (TB) cases have nearly doubled, with proportionately much greater increases in smear-negative and extrapulmonary cases compared with smear-positive cases. At the same time, HIV infection has become widespread throughout the country. This survey was undertaken in order to study the association of TB and HIV and to determine the impact of HIV on present and future TB cases in Tanzania.

The survey design provided for HIV testing of a representative country-wide sample of approximately one-sixth of all new and relapse cases registered between January 1991 and December 1993, with linkage to demographic, clinical and bacteriological data for these cases. HIV surveillance data were used for comparison purposes.

A total of 6928 TB cases from all of the country's 20 mainland regions were tested. The overall HIV seroprevalence was 32%. Both crude and adjusted odds ratios (OR) for HIV infection were higher in women, those aged 25-44 years, urban residents, cases of smear-negative and extrapulmonary disease, and persons with a bacille Calmette-Guérin (BCG) vaccination scar. The age-and sex-adjusted relative risk for HIV infection in TB patients compared to blood donors in the same regions was 7.1 (95% confidence interval, 6.6-7.5), and was significantly higher among those aged 25-34 years. Of 3360 patients with bacteriological culture results 46% were culture-positive for Mycobacterium tuberculosis. Drug susceptibility tests were performed on 1164 isolates with the overall rate of drug resistance of 6.2%. Rates of initial resistance were low in both HIV-positive (4%) and HIV-negative (5.8%) patients. Rates of acquired resistance were higher (19% overall) and did not vary significantly by HIV serostatus. Initial combined resistance to both isoniazid and rifampicin was uncommon (0.4%) as was monoresistance to rifampicin (0.3%).

The higher OR for women and young adults reflect the higher rates of HIV infection in those populations. The finding that smear-positive relapse cases were no more likely to have HIV infection than new smear-positive cases suggests that the treatment regimen for new cases is effective in HIV-associated TB. The low rates of both initial and acquired drug resistance in HIV-positive patients is further evidence of adequacy of treatment. The higher relative risk for HIV infection among patients aged 25-34 years suggests increased HIV-related TB transmission. Finally, it is estimated that approximately two-thirds of the increase in the rate of smear-positive tuberculosis in the country can be directly attributed to HIV infection.