Incidence of hepatitis A virus infection among an Italian military population.

In 1990, a prospective serological survey to estimate the rate of clinical and inapparent infection with hepatitis A virus (HAV) was performed in a cohort of 1,268 soldiers, 18-24 years old, during an 8 month period in the Campania region in Italy. At the time of enrollment 318 (25%) of the 1,268 soldiers were positive for total antibodies to HAV (anti-HAV). None of them was positive for IgM anti-HAV. Among the 950 susceptible subjects who were followed up for 8 months, eight (0.8%) later seroconverted to anti-HAV positivity. This figure corresponds to an incidence of 1.3/100 person/years (eight seroconversions during 633.3 years of observation). There were two clinical (with presence of IgM-anti-HAV) and six inapparent infections. The clinical/subclinical HAV ratio was 1:3. These findings indicate that the risk of HAV infection among soldiers residing in this area is not negligible.