[The epidemiology of hepatitis A in the Netherlands, 1957-1998]

To describe the incidence of hepatitis A in the Netherlands, 1957-1997 to find an explanation for the increase in 1998.

Descriptive.

National Institute of Public Health and Environment (RIVM), Bilthoven, the Netherlands.

Following an increase of the number of hepatitis A notifications in 1998 the national notification data over the period 1957-1997 were examined. The impact of waning natural immunity in the Dutch population and of the annual influx from high-endemic countries on the epidemiology of hepatitis A was studied.

The number of notifications declined considerably in the early sixties and stabilised in the seventies at 5-7 notifications per 100,000 inhabitants. The age distribution over time showed that the proportion of cases in children is still the largest, although the proportion of notifications of adult cases increased slightly over time. A seasonal fluctuation was demonstrated by a steep increase in the number of notifications among non-Dutch children in autumn, with the infection acquired abroad, probably in Morocco or Turkey, followed by an increase among children and adults who acquired their infection in the Netherlands. The number of notifications doubled in the early months of 1998 compared with 1997. The present epidemic increase can be explained by increased transmission in subgroups who contributed similarly in the same months in the past 5 years and may result from secondary infections related to the relatively high peak in autumn in 1997.

In 1975-1997 a stable but low incidence of hepatitis A was observed in the Netherlands; the number of cases among adults did not increase over time. The present epidemic increase underlines the potential risk of epidemics and the role of importation of the virus from high-endemic countries.