Can Having Fewer Partners Increase Prevalence of Aids?

Under asymmetric information about sexual history, sexual activity creates externalities. Abstinence by those with few partners perversely increases the average probability of HIV infection in the pool of available partners. Since this increases prevalence among the high activity people who disproportionately influence the disease's future spread, it may increase long-run prevalence. Preliminary calculations using standard epidemiological models and survey data on sexual activity suggest that most people have few enough partners that further reductions would increase steady-state prevalence. To the extent the results prove robust, they suggest that public health messages will be more likely to reduce steady-state prevalence and create positive externalities if they stress condom use rather than abstinence.