HETEROSEXUAL TRANSMISSION OF HUMAN-IMMUNODEFICIENCY-VIRUS - VARIABILITY OF INFECTIVITY THROUGHOUT THE COURSE OF INFECTION

Although individuals infected with human immunodeficiency virus (HIV) seem to be more infectious in the late stages of HIV infection and pos sibly also during the seroconversion period, most estimates of per-sex ual-contact infectivity have been obtained without allowing for variab ility over the course of infection, in this analysis, a probabilistic model was fitted to data from a European study carried out between 198 7 and 1992 that involved 499 (359 males and 140 females) HIV-infected subjects (index cases) and their regular heterosexual partners. The mo del used allowed infectivity (the per-sexual-contact HIV transmission probability, mu) to vary through three stages: the first 3 months foll owing infection, the subsequent asymptomatic period, and the advanced stage (HlV-related clinical symptoms or a CD4-positive T lymphocyte co unt less than 200/mm(3)). Male-to-female infectivity through penile-an al sex was found to be higher in both the early and advanced stages of infection (mu = 0.183) than in the longer intermediate period (mu = 0 .014) (p < 0.03), Failure to demonstrate significant differences betwe en stages for other types of contact (male-to-female penile-vaginal co ntacts: mu = 0.0007; female-to-male transmission: mu = 0.0005) may ref lect insufficient power rather than a true lack of variability. Indeed , the results for penile-anal sex suggest.that persons who are in the process of seroconverting may be much more infectious than asymptomati c infected persons, whatever the type of contact. Prevention education should stress the risk of HIV transmission from subjects who may be u naware of their infection.