Recent studies have indicated variation in the infectivity beta of HIV among heterosexual couples. We represent this heterogeneity by modelling beta as a random variable. Using data on the number of contacts and seroconversion of couples, we fit the model by maximum-likelihood estimation with a beta distribution and a discrete distribution for beta. The estimates indicate the heterogeneity is extreme. The limitations of the model and the implications of the results for epidemiologic spread and further research are discussed.
Wiley et al. (Sun,) studied this question.