The shift in prevalence of hepatitis A immunity in Flanders, Belgium.

The purpose of this study was to obtain data on the prevalence of hepatitis A in Flanders, Belgium, in order to analyse any change in the epidemiological pattern of hepatitis A virus (HAV) in the region, and to determine at which age pre-vaccination testing would be useful. To meet these goals, a sero-epidemiological survey was conducted: 4058 serum samples were collected from a random sample of the general population in 1993-94. The overall age-standardised prevalence was 51.3%. Among non-Belgians (N = 245), the age-standardised anti-HAV prevalence was 66.4%, significantly higher than the 49.6% anti-HAV prevalence found in Belgians (N = 3186). Among Belgians, seroprevalence increased with age: from 5.4% in the youngest age group (0-14 years) to over 80% in the two oldest age groups (55-64 years and > or = 65 years). Prevalence rates were as high as 31.7% in the 25-34 year old age category, and 60.8% in the 35-44 year old age category. The age-specific prevalence figures among Belgians and non-Belgians reflect two different epidemiological patterns: the epidemiological pattern of a low endemic region for Belgians and the epidemiological profile of an intermediate endemic region forn non-Belgians. The age-specific prevalence figures in Belgians were compared with the 1979 and 1989 anti-HAV prevalence figures in Belgian first-time blood donors. A clear epidemiological shift showing decreasing HAV prevalence in the youngest age groups was found. If we accept that pre-vaccination screening is useful at a 35% prevalence rate, all persons over 35 years of age should be screened before vaccination.