Resurgence of Sexually Transmitted Hepatitis C Virus Infection in Men Who Have Sex With Men Living With HIV.

In 2023-2025, HCV transmission in men who have sex with men (MSM) living with HIV in Hong Kong resurged. This study aims to assess the epidemiologic patterns between 2011 and 2025. Among 288 MSM with sexually acquired HCV infection, 73% were diagnosed at least 12 months after HIV diagnosis, and 98% had ever achieved HIV viral load suppression. Comparing with Period 1 (2015-2022) featuring a large HCV genotype 3a cluster (89 diagnoses) and a few smaller HCV genotype 1a clusters (size of 2 to 13), Period 2 (2023-2025) was dominated by two HCV genotype 1a clusters (7 and 16 new diagnoses). Transmission of genotype 3a viruses subsided in Period 2, with only 3 new diagnoses. Comparing with Period 1, a higher proportion of MSM with HCV diagnoses in Period 2 self-reported sexualised injecting drug use (OR = 3.82, 95% CI 1.59-9.20) and HCV direct-acting antivirals therapy (no treatment as reference group, OR = 3.72, 95%CI 1.82-7.60). The epidemic rebound by a different HCV genotype was likely contributed by increased engagement in chemsex and post-COVID-19 population mobility.