CIRCULATION OF POLIOVIRUS DURING THE POLIOMYELITIS OUTBREAK IN THE NETHERLANDS IN 1992-1993

A population-based study on the circulation of epidemic poliovirus dur ing the 1992-1993 outbreak in the Netherlands was carried out in order to assess whether the virus circulated outside the group of people wh o reject vaccination on religious grounds and outside the area where t hese groups form a sociodemographically closely knit network. The prev alence of poliovirus excretion was estimated in a cross-sectional stud y with a random sample of 2,400 children aged 5-14 years and 3,000 adu lts aged 40-64 years; the sample was drawn from the municipal populati on registers in four regions (three inside and one outside the risk ar ea). Fecal samples for virus isolation and characterization were submi tted by mail, and a questionnaire was completed with age, sex, type an d level of education, vaccination history, and religious denomination. Both a completed questionnaire and a fecal sample were received from 3,182 persons (response, 58.9%). Wild poliovirus was isolated only fro m children within the risk group and in the area at risk. The crude ex cretion rate of the epidemic poliovirus type 3 per 1,000 persons was 2 .5, but it amounted to 70.7 for those belonging to Orthodox Reformed c hurches. The prevalence of vaccine virus excretion per 1,000 persons w as 10.2 for children and 5.2 for adults. It was concluded that, during the 1992-1993 outbreak, the risk of poliomyelitis was restricted to r eligious subpopulations rejecting vaccination. The lack of evidence of poliovirus circulation outside these groups at risk supports the hypo thesis that herd immunity is sufficiently maintained in a population v accinated with inactivated polio vaccine.