Hiroshi Yotsuyanagi

Although the prevalence of hepatitis C virus (HCV) infection has decreased significantly with the advent of direct‐acting antiviral agents, HCV is known to spread as a sexually transmitted disease among men who have sex with men (MSM), and this study aims to provide a perspective on the future prevalence of HCV in Japan. We examined incidence in two groups of MSM with HIV attending our institution in this retrospective cohort study, from 2009 to 2019 and from 2020 to May 2023 and investigated their background factors. Twenty‐two cases were newly confirmed to be HCV infection in 2009–2019 and a total of 9 cases in 2020–2023, with an incidence rate of 5.04 per 1000 person‐years in 2009–2019 and 5.55 per 1000 person‐years in 2020–2023. All of them were diagnosed at routine outpatient visits for HIV, and few cases were considered to have symptoms of suspected hepatitis that led to a visit to the hospital and a diagnosis of HCV. Although HCV is still prevalent among MSM in Japan, it is possible that it would not have been diagnosed without testing at regular visits as in the case of people with HIV, and that the true prevalence rate among MSM, including non‐HIV‐infected persons, may be much higher.