Incident hepatitis C virus infection in a community-based population in Japan.

Hepatitis C virus (HCV) is an important cause of liver disease throughout the world. However, the natural history and pathogenesis of this infection is still not completely understood. The aim of this study was to characterize the evolution of incident, asymptomatic HCV infection in a community-based population in Japan. The Miyazaki Cohort Study is a prospective study of adult residents in two villages, one of which has a very high prevalence of HCV. Nine hundred and seventy-three people from this village were enrolled in the cohort between 1984 and 1995, with antibodies to HCV (anti-HCV) found in 23%. During subsequent visits to annual health screens, new HCV seroconverters were identified among susceptible individuals, and their sequential samples were tested for anti-HCV, HCV-RNA, and HCV core antigen. Fourteen participants (six males, eight females) acquired anti-HCV during the first 11 years of study follow-up, at an incidence rate of 362 per 100 000 person-years. Detectable HCV-RNA and high anti-HCV titres (> 1:2048) were observed for more than 5 years following seroconversion in 80% (8/10) of seroconverters with sufficient information, indicating the development of persistent infection in these subjects. Three (37.5%) of the eight sero converters with persistent infection had fairly consistent, albeit mild, alanine aminotransferase elevations (30-130 IU/L) during the study. Anti-HCV seroconversions occurred at a very high rate in this community-based population in Japan, in which this infection is endemic. Persistence also developed at a high frequency among the cases of newly acquired infection, although the associated liver enzyme abnormalities were mild.