Incidence of sexually transmitted hepatitis C virus infection among men who have sex with men in Japan from 2009 to 2023

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.

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.

K E Y W O R D S
HCV, hepatitis C, HIV, men who have sex with men, sexually transmitted disease The prevalence of chronic hepatitis C and hepatitis C virus (HCV) carriers has decreased significantly in Japan due to the widespread use of direct-acting antivirals (DAA) treatment and the almost complete absence of acute hepatitis C caused by blood transfusions, needlestick injuries, and mother-to-child transmission. 1 Because of a significant decrease in the size of the population of potential reservoirs of infection, the prevalence of HCV is expected to decline further in the future. 2 However, in the field of medical care for people with HIV (PWH), it is known that sexually transmitted HCV infection is prevalent among men who have sex with men (MSM). 3,4 The purpose of this study is to examine the incidence of HCV infection, patient backgrounds, and diagnostic opportunities, and to provide a perspective on the future HCV epidemic in Japan.   The demographics of the cases were not significantly different between the two periods, but there were many anti-TP positive and anti-hepatitis B core antibody-positive cases overall, which can be said to be common among sexually active MSM. Some patients newly infected with HCV were presumed to be substance abusers, so "chemsex" would also be a risk factor. 7 Symptoms of acute hepatitis C were found in more than half of the cases, but most of them were detected either during a routine visit for HIV or after anti-HCV antibody screening tests for other purposes; therefore, it is likely that many of the patients in Not only for HCV, but likewise for all STDs, sexually active MSM are at the same increased risk of STDs regardless of whether or not they are PWH, and are likely to remain undiagnosed. 8,9 HIV postexposure prophylaxis (PrEP) is becoming more widespread worldwide, and the number of HIV-PrEP users is increasing in Japan. 10 Increasing opportunities for hospital visits and testing for STDs would lead to the uncovering of undiagnosed STDs. [9][10][11] Therefore, physicians need to be made widely aware of the need to consider HCV as an STD.
One limitation of this study is that it is a retrospective cohort study and the observation period is the time during which blood tests

CONFLICT OF INTEREST STATEMENT
The authors declare no conflicts of interest.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

ETHICS STATEMENT
Ethics approval was granted by the ethics board of the Institute of Medical Science, University of Tokyo (2022-48-1128).