Maternal exposure to influenza and risk of schizophrenia: a 22 year study from The Netherlands.

We investigated any effect of prenatal exposure to influenza during gestation on subsequent risk of schizophrenia using a national sample from The Netherlands. Dates of births of all Dutch-born schizophrenia (ICD-9) patients (n = 10,630) admitted to hospitals for the first time between 1970 and 1992 were examined in relation to the occurrence of influenza epidemics between 1947 and 1969. As a measure of prevalence of influenza, the number of deaths from influenza per month in The Netherlands was used. A Poisson regression analysis revealed that an increase in the prevalence of influenza 3 months prior to birth was followed by an increase in births of preschizophrenics, although this fell outside statistical significance (p = .11). However, the effect became marked in typical schizophrenics (n = 4726), but not in less typical cases (n = 5389). For typical schizophrenics, the parameter estimate derived from the regression model indicates that there was a 10% increase (95% confidence interval: -1 to 22%) in preschizophrenic births for every 500 deaths from influenza 3 months before birth.