The multicentre study on factors determining the differential spread of HIV in four African cities: summary and conclusions.

In all regions of sub-Saharan Africa, the predominant mode of transmission of HIV is sexual intercourse between men and women, but there are large variations in the rate and extent of the spread of HIV in different populations. We set out to try and identify factors that could explain why HIV has spread more rapidly in some parts of Africa than in others. To approach this question, we used a study design that combined ecological comparisons across populations with individual-level analyses within populations. The ecological analysis allowed us to explore the population-level effects of risk factor profiles that may be difficult to identify from individual-level analysis.