Ecological and individual level analysis of risk factors for HIV infectionin four urban populations in sub-Saharan Africa with different levels of HIV infection

Objective: To identify factors that could explain differences in rate of sp read of HIV between different regions in sub-Saharan Africa. Design: Cross-sectional study. Methods: The study took place in two cities with a relatively low HIV preva lence (Cotonou, Benin and Yaounde, Cameroon), and two cities with a high HI V prevalence (Kisumu, Kenya and Ndola, Zambia). In each of these cities, a representative sample was taken of about 1000 men and 1000 women aged 15-49 years. Consenting men and women were interviewed about their socio-demogra phic background and sexual behaviour; and were tested for HIV, herpes simpl ex virus type 2 (HSV-2), syphilis, Chlamydia trachomatis and Neisseria gono rrhoea infection, and (women only) Trichomonas vaginalis. Analysis of risk factors for HIV infection was carried out for each city and each sex separa tely. Adjusted odds ratios (aOR) were obtained by multivariate logistic reg ression. Results: The prevalence of HIV infection in sexually active men was 3.9% in Cotonou, 4.4% in Yaounde, 21.1% in Kisumu, and 25.4% in Ndola. For women, the corresponding figures were 4.0, 8.4, 31.6 and 35.1%. High-risk sexual b ehaviour was not more common in the high HIV prevalence cities than in the low HIV prevalence cities, but HSV-2 infection and lack of circumcision wer e consistently more prevalent in the high HIV prevalence cities than in the low HIV prevalence cities. In multivariate analysis, the association betwe en HIV infection and sexual behavioural factors was variable across the fou r cities. Syphilis was associated with HIV infection in Ndola in men [aOR = 2.7, 95% confidence interval (CI) = 1.5-4.9] and in women (aOR = 1.7, 95% Cl = 1.1-2.6). HSV-2 infection was strongly associated with HIV infection i n all four cities and in both sexes (aOR ranging between 4.4 and 8.0). Circ umcision had a strong protective effect against the acquisition of HIV by m en in Kisumu (aOR = 0.25, 95% Cl = 0.12-0.52). In Nclola, no association wa s found between circumcision and HIV infection but sample sizes were too sm all to fully adjust for confounding. Conclusion: The strong association between HIV and HSV-2 and male circumcis ion, and the distribution of the risk factors, led us to conclude that diff erences in efficiency of HIV transmission as mediated by biological factors outweigh differences in sexual behaviour in explaining the variation in ra te of spread of HIV between the four cities. (C) 2001 Lippincott Williams & Wilkins.