HIV infection and silicosis: the impact of two potent risk factors on the incidence of mycobacterial disease in South African miners

Objective: To investigate the combined effects of HIV infection and silicos is on mycobacterial disease Design and setting: A retrospective cohort of 1374 HIV-positive and 2648 HI V-negative miners who attended a South African gold mining hospital and pri mary health clinics. Participants: Miners who had been tested for HIV, with consent, at primary health clinics during 1991-1996, predominantly because of a symptomatic sex ually transmitted disease. Results: Tuberculosis (TB) incidence was 4.9 and 1.1 per 100 person-years i n HIV-positive and HIV-negative miners respectively. The incidence of Mycob acterium kansasii disease was also high (0.32 and 0.10 per 100 person-years , respectively). Silicosis was highly prevalent, implying inadequate dust c ontrol, and was a significant TB risk factor among both HIV-positive and HI V-negative men (adjusted incidence rate ratios 1.4-2.5 according to radiolo gical severity). The data were consistent with the risks of silicosis and H IV combining multiplicatively, but did not fit an additive model. The incid ence of HIV-associated TB increased significantly during the study, with no corresponding change in HIV-negative rates, to reach 16.1 per 100 person-y ears among HIV-positive silicotics. Conclusions: The risks of silicosis and HIV infection combine multiplicativ ely, so that TB remains as much a silica-related occupational disease in HI V-positive as in HIV-negative miners, and HIV-positive silicotics have cons iderably higher TB incidence rates than those reported from other HIV-posit ive Africans. The increasing impact of HIV over time may indicate epidemic TB transmission with rapid disease development in HIV-infected miners. Simi lar but currently unrecognized interactions may be contributing to TB contr ol problems in other industrializing countries affected by the HIV epidemic . (C) 2000 Lippincott Williams & Wilkins.