Background Viral sorting is a risk reduction strategy based on the perception that an undetectable viral load reduces HIV transmission risk during unprotected anal intercourse (UAI) with casual partners. We examined how frequently HIV-positive men who have sex with men (MSM) practice intentional viral sorting with HIV-positive and HIV-negative or unknown casual sex partners and sex buddies.

Methods We included 177 HIV-positive MSM who completed a questionnaire regarding UAI and viral sorting practice. Viral sorting was defined as intentionally engaging in UAI on the condition that both the participant and the HIV-positive partner had an undetectable viral load, or the participant himself had an undetectable viral load with an HIV-negative/unknown casual partner. We examined whether men ever practiced intentional viral sorting since HIV diagnosis, and how often UAI with a last casual partner was the result of viral sorting. We distinguished two casual partner types: the casual sex partner (met by chance and had sex with”) and the sex buddy (“contacted on a regular basis for sex but not considered a steady partner”).

Results Of the 177 participants, 68% (120/177) ever had UAI since HIV diagnosis. Of those, 44% (53/120) ever practiced viral sorting with an HIV-positive partner and 38% (46/120) with an HIV-negative/unknown partner. Of all participants, 41% (73/177) had UAI with a last casual partner. Among men who had UAI with a last HIV-positive casual partner (n=35), proportions of viral sorting practice with a casual sex partner and a sex buddy were, respectively, 20% (3/15) and 58% (11/20), p<0.05. Among men who had UAI with an HIV-negative/unknown casual partner (n=38), proportions of viral sorting with a casual sex partner and a sex buddy were, respectively, 57% (16/28) and 40% (4/10), p=0.47.

Conclusions Our data suggest that viral sorting as an intentionally practiced HIV risk reduction strategy is applied relatively frequently among HIV-positive MSM with all partner types. The highest proportions were reported with HIV-positive sex buddies and HIV-negative/unknown casual sex partners. Since viral sorting is being extensively applied by MSM and most of the available data on viral load and HIV transmission risk is derived from studies on heterosexuals, future investigation should provide clear-cut indications on the effectiveness of viral sorting in lowering HIV transmission among MSM.