Hepatitis A incidence and hospital-based seroprevalence in Italy: a nation-wide study.

To define the pattern of HAV infection in Italy and to study the differences among geographic areas (northern, central and southern Italy) and age-classes, we performed HAV antibody testing on sera collected in 1996-1997 from a large sample of the Italian population and compared the results with those of other seroprevalence studies and with incidence data for the period 1985-2005, calculated by a surveillance system specific for acute viral hepatitis based on symptomatic cases. A total of 3,561 sera, collected by hospital-based reference laboratories in 18 out of 20 Italian Regions, were tested; 1,138 (32%, 95% CI: 30.5-33.5) were positive. The age-adjusted prevalence was 60.1% and the age-specific rates were among the highest rates reported in Europe in the 1990s. The age-adjusted seroprevalence showed a significant north-south gradient, increasing from 55% in northern Italy to 68% in southern Italy. Age and area of residence were found to be strong predictors of previous HAV infection: the marked increase in prevalence with increasing age represents a strong cohort effect. In northern Italy, a marked increase with age was observed beginning with the 20- to 29-year age-class, whereas in southern Italy, such an increase was observed beginning with the 12- to 19-year age-class, indicating that northern Italy preceded southern Italy by 10-20 years in terms of improvements in hygiene and sanitation. The incidence of HAV infection shows an evident peak in 1997, when an outbreak occurred in southern Italy, mainly affecting 15- to 24-year-old individuals. In the period from 1998 to 2005, the incidence drastically decreased (average of 3.2/100,000 inhabitants), reaching a minimum of 2/100,000 inhabitants in 2005.