Low incidence of hepatitis C among a cohort of HIV-negative gay and bisexual men using HIV pre-exposure prophylaxis (PrEP) in Melbourne, Australia, and the contribution of sexual transmission.

BACKGROUND PrEPX was an Australian HIV pre-exposure prophylaxis (PrEP) study conducted between 2016 and 2018. This analysis aimed to estimate hepatitis C (HCV) incidence and explore likely modes of transmission. SETTING Cohort study of PrEP users in Victoria, Australia. METHODS HCV tests were conducted at enrolment and every 12 months thereafter. HCV incident cases were identified from laboratory data. Likely modes of transmission were inferred from computer-assisted self-interviews (CASI), medical records, and interviews. RESULTS Among 3,202 PrEPX participants tested for HCV at baseline, HCV RNA-positive prevalence was 0.22% (95% CI 0.09-0.45). Among participants testing HCV antibody- or RNA-negative at baseline, 2,058 had at least one follow-up HCV test. Eight incident HCV cases were identified during 2,111 person-years of follow-up (incidence 0.38/100 person-years); all were primary infections in men who had sex with men (MSM). Clinical, laboratory and CASI data were available for all, and six cases were interviewed. Three cases were attributable to injecting drug use (IDU). A fourth case reported IDU, but his HCV was attributable to sexual transmission. Four other cases reported no IDU and probably acquired HCV sexually. Most cases reported anal trauma in the context of condomless receptive anal intercourse during group sex at sex-on-premises venues (SOPV). CONCLUSION Incident HCV was uncommon in PrEPX compared to international PrEP studies, and most cases were transmitted sexually. Our findings highlight the need for HCV prevention messaging by clinicians, in SOPV and on digital platforms utilised to arrange group sex, and for HCV screening among some PrEP-using MSM.