Epidemiologic evidence for time variation in HIV infectivity

Data from three epidemiologic studies of heterosexual transmission of HIV a mong monogamous couples are used to assess evidence for time variation in H IV infectivity, possibly related to varying levels of infectiousness follow ing infection in the primary infected partner. Analyses are based on statis tical techniques that account for the inherent incompleteness of exposure i nformation from such studies, and that allow direct assessment of the hypot heses that infectivity varies with time since infection and across partners hips. Data include findings from 302 couples from the California Partners' Study and 51 and 31 couples, respectively, from two U.S. Center for Disease Control and Prevention (CDC)-sponsored studies of infection in partners of transfusion recipients. Results indicate weak evidence for higher infectiv ity following infection of the primary partner, decreasing to relatively lo wer levels from 2 to 10 years after. Although these findings are consistent with biologic observations of time Variation in viral levels, other explan ations of the observed pattern (e.g., heterogeneity of infectivity) are equ ally plausible, pointing out some inherent limitations of data from such st udies.