Determinants of acquiring hepatitis A virus disease in a large Italian region in endemic and epidemic periods.

Viral hepatitis A is endemic in Puglia region (southeast Italy). Over the last 13 years, annual incidence rates have ranged from 4 to 138 per 100,000 inhabitants and periodical regional epidemics have been described. Between 1 January 1996 and 31 December 1997 over 11,000 cases of hepatitis A were reported accounting for an annual incidence rate over 130/100,000. To identify exposures during the epidemics, a case-control study was performed in two different rounds and since 1997, an enhanced surveillance system has permitted the monitoring of exposures of subsequent cases. Raw seafood consumption was identified as the major risk factor for hepatitis A. Adjusted odds ratio and 95% confidence intervals for this exposure from the first round of the case-control study was 38.6 (12.2-122.4) and for the second round for consumption of raw mussels it was 30.7 (16.0-52.0). Hepatitis A epidemiology in Puglia is consistent with an endemic situation sustained by locally contaminated seafood consumed raw and by the recurrence of large epidemics, where size is influenced by the accumulation of susceptible subjects in the population.