HIV-1 infection as a risk factor for the development of tuberculosis: a case-control study in Tanzania

A population-based case-control study was carried out in Mwanza Region, Tanzania, to determine the relative and population attributable risk of human immunodeficiency virus type 1 (HIV-1) infection for developing active tuberculosis. Cases were 441 consecutively diagnosed patients with tuberculosis (all types), aged 15-54 years. Controls were a representative population sample of 4161 people, drawn in a stratified cluster sample from urban areas, roadside settlements, and rural villages. HIV-1 infection was determined by ELISA and if the ELISA result was indeterminate by Western Blot. The HIV-1 prevalence in cases was 23.0% in rural, 32.1% in roadside, and 54.1% in urban areas, while in controls these prevalences were 3.4%, 7.2% and 12.1% respectively. The relative risk (RR) of HIV-1 infection for the development of active tuberculosis was estimated to be 8.3 (95% confidence interval [CI] 6.4-11.0). This risk varied little by sex or residence, but appeared to be more pronounced in the age group 25-34 years. The case detection rate of tuberculosis in those aged 15-54 years was 125/100,000 people per year. The population attributable risk was 36/100,000 people per year, implying that 29% of tuberculosis cases at present may be attributable to HIV-1 infection. It is concluded that HIV-1 infection is a major contributing factor to the increased case detection rate of tuberculosis observed over the past 10 years in Mwanza Region. If the prevalence of HIV-1 continues to increase, the incidence of tuberculosis will continue to rise as well.(ABSTRACT TRUNCATED AT 250 WORDS)