Introduction Low HIV serostatus awareness and delayed treatment initiation among people living with HIV (PLHIV) contribute to HIV sexual transmission. An unacceptably low proportion of PLHIV are aware of their HIV status in Latin America. Improved understanding of sexual risk among PLHIV could help guide HIV prevention strategies.

Methods A cohort of 401 men who have sex with men (MSM) and transgender women at high risk were enrolled and assessed every three months for condomless sex and sexually transmitted infections (i.e. syphilis, HIV and anal chlamydia, and anal gonorrhoea). Among those who were positive at entry, we compared condomless sex and anal chlamydia/gonorrhoea according to prior knowledge of HIV serostatus; among those who seroconverted during follow-up, we compared condomless sex and anal chlamydia/gonorrhoea before vs. after HIV diagnosis, using McNemar’s Chi-square test.

Results At baseline, 82 (20.5%) participants self-identified as HIV positive and an additional 42 (10.5%) were diagnosed with HIV. Among the 42 unknown HIV positives, 71% reported recent condomless receptive anal sex compared to 55% of known HIV positives (p-value = 0.078). No difference was observed in condomless insertive anal sex; 48% in each group. Among the 24 sero-converters during follow-up, 79% reported condomless receptive anal sex prior to their diagnosis and 32% after their diagnosis (59% decline, p-value = 0.001); 46% reported condomless insertive anal sex prior to their diagnosis and 14% after diagnosis (70% decline, p-value = 0.011). Anal gonorrhoea and/or chlamydia were diagnosed among 46% prior and 27% after diagnosis among the observed sero-converters (41% decline, p-value = 0.096).

Conclusions Risk behaviours and concurrent STIs diminish after a new diagnosis, following the patterns previously reported elsewhere. Current prevention efforts for PLHIV are insufficient and must take into account motivations for sexual risk taking, encourage people to reach viral suppression, and improve available prevention strategies to prevent onward transmission of HIV.

Disclosure of interest statement None.