Adult major affective disorder after prenatal exposure to an influenza epidemic

Background: We have previously reported an increase in schizophrenia diagnoses in a population exposed during the second trimester to the 1957 influenza epidemic. These basic findings together with a fair number of replications have been interpreted as supporting a neurodevelopmental contribution to the origins of schizophrenia. Recent neuroimaging findings suggest that affective illness may also have a neurodevelopmental origin. We examined the hypothesis that exposure to an influenza epidemic during the second trimester would increase the risk for adult major affective disorder. Methods: The subjects had been exposed as fetuses to the type A2/Singapore influenza epidemic in greater Helsinki, Finland. Control subjects were born in the 6 years before the epidemic. Results: We found a significant ( P P P >.05) were similar. The second-trimester effect remained when we estimated population-based rates (2.1 vs 0.6 per 1000) ( P P P >.05) elevation was observed for the bipolar forms of major affective disorder. Conclusions: These data are consistent with the hypothesis concerning the possible neurodevelopmental contribution to the origins of some forms of major affective disorder, especially unipolar depressive disorder. These encouraging findings, if replicated, may suggest that some mental disorders may stem, in part, from a disturbance in the development of the fetal brain during the second trimester.