March 1990

An Update on the Helsinki Influenza Project

Author Affiliations

Social Science Research Institute University of Southern California University Park Los Angeles, CA 90089-MC-1111
Department of Psychology Loyola Boulevard at W 80th St Loyola Marymount University Los Angeles, CA 90045
Department of Psychiatry University of Helsinki Lapinlahdenti SF 00180 Helsinki 18 Finland

Arch Gen Psychiatry. 1990;47(3):292. doi:10.1001/archpsyc.1990.01810150092021

To the Editor.—  Helsinki residents exposed to the 1957 type A2 influenza epidemic during their second trimester of fetal development evidenced a significantly increased risk of schizophrenia at age 26 years 2 months.1 We have reported a population-based rate of 11.6 per 1000 for those exposed during the second trimester. The rates for the first and third trimesters were 5.8 per 1000 and 6.2 per 1000, respectively. As controls for these subjects, we collected data on those born in 1951 to 1956 in Helsinki.As part of a study involving a clinical follow-up of these cases, we have recently completed an updated search for this cohort in the greater Helsinki psychiatric hospitals. We have accepted psychiatric admissions through the age of 29.8 years.We have identified an additional 448 "new cases" (55 new index and 393 new controls), bringing our total sample to 2229. The population-based schizophrenia rate for

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