Sexually transmitted infection as a risk factor for homosexual HIV transmission: a systematic review of epidemiological studies

Existing reviews suggest some sexually transmitted infections (STIs) are risk factors in heterosexual HIV transmission. This may not be so in homosexual HIV transmission, about which reviews make no specific conclusions. This paper reviews published studies which report on the relative risk of STIs in HIV seroconversion in homosexually-active men in order to examine this matter. Papers obtained via various searches were judged adequate if they were prospective cohort or cohort-nested case-control studies; used HIV seroconversion as the outcome; assessed STI exposure objectively; and controlled for potential confounding from age and sexual behaviour. Sixteen papers were obtained, of these 3 were judged adequate. Adequate papers reported little association. Inadequate papers were more likely to report association. Evidence from adequate studies does not suggest STIs are risk factors in homosexual HIV transmission. Some caution is needed in interpreting the results because of the paucity of adequate studies.