Community effects on the risk of HIV infection in rural Tanzania

Objectives: To investigate the effect of community characteristics on HIV prevalence and incidence. Methods: Data from an open cohort study with demographic surveillance, epidemiological surveys, and qualitative research were used to examine the association between individual and community risk factors with HIV prevalence in 1994-5 and incidence between 1994-5 and 1996-7 among men (n=2271) and women (n=2752) living in a rural area in northwest Tanzania. Using subvillages as the unit of analysis, community factors investigated were level of social and economic activity, ratio of bar workers per male population aged 18-59, level of community mobility, and distance to the nearest town. Logistic and Cox regression models were estimated to assess community effects, controlling for multiple individual factors. Results: All four community factors had strong effects on HIV transmission. Men who lived in subvillages with the highest level of social and economic activity had an odds of being HIV positive that was about five times higher (OR=4.71, 95% CI=2.89 to 6.71) than those in places with low levels of activity; women in these subvillages had an odds that was twice as high (OR=1.92, 95% CI=1.27 to 2.92). After controlling for community effects, the effects of some individual factors on the risk of HIV-education, male circumcision, type of work, and number of household assets-changed notably. The association between HIV incidence and community factors was in the expected direction, but did not reach statistical significance (RR=2.07, p=0.10). Conclusions: Results suggest that community characteristics play an important part in the spread of HIV in rural Tanzania. Community effects need both to be considered in individual risk factor analyses and be given more attention in intervention programmes.