A microsimulation study of the effect of concurrent partnerships on the spread of HIV in Uganda

This paper examines the potential impact of concurrent partnerships on HIV spread in Uganda using microsimulation. We represent a population of individuals, the sexual partnerships that they form and dissolve over time, and the spread of an infectious disease as a stochastic process. Data from the 1994 Ugandan sexual network survey are used to establish baseline outcomes, and the baseline is compared to sequential monogamy, increased concurrency and increased number of partnerships. The observed level of concurrency raises the number of infected cases by about 26% at the end of 5 years compared to sequential monogamy. Increasing both the number of partnerships and the rate of concurrency together has a stronger impact than increasing either alone. If risk behaviors were slightly higher at the start of the Ugandan epidemic, concurrency may have amplified the prevalence of HIV by a factor of 2 or 3. The public health implications are that data must be collected properly to measure the levels of concurrency in a population, and that messages promoting "one partner at a time" are as important as messages promoting fewer partners.