Viral Exposure Boosts Schizophrenia Risk

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Viral Exposure Boosts Schizophrenia Risk

For about a month in the fall of 1957, Helsinki, Finland, was swept by a serious Type A2 influenza virus epidemic that is estimated to have infected two-thirds of the population. Thanks to the meticulous record-keeping of the Finnish government, researchers now have established that people who were exposed to the worldwide epidemic while in their second trimester of fetal development have an increased risk of hospitalization for schizophrenia.

"A basic risk for schizophrenia seems to occur when there is some kind of fetal trauma during the second trimester,' says psychologist and research director Sarnoff A. Mednick of the University of Southern California in Los Angeles. "It is not so much the type of stress as it is the timing of stress during gestation which is critical in determining the risk.'

But, importantly, he and his colleagues report they have found a link between second-trimester exposure to a specific virus and the adult diagnosis of schizophrenia. Longstanding theories of an "infection connection' in some cases of schizophrenia have generated more debate than data (SN: 11/30/85, p.346). The Finnish study, which will appear later this year in ARCHIVES OF GENERAL PSYCHIATRY, was generated by the researchers' ongoing, 24-year study of Danish children with schizophrenic mothers. Children who developed schizophrenia in adulthood and had an excess of birth complications also tended to have been born during periods of increased viral infections (January, February and March) in crowded Copenhagen.

For the county encompassing Helsinki, the investigators tracked all children born in the nine months immediately followint the 1957 epidemic who were hospitalized before the age of 26 in one or more of the county's eight psychiatric facilities. These 216 "index' individuals were compared with 1,565 "control' children born in the same county in the corresponding months of the previous six years, and who were hospitalized for psychiatric disorders before 26 years of age.

Nearly 36 percent of the index patients exposed to the epidemic during their second trimester of fetal development were diagnosed as schizophrenic by Finnish psychiatrists. …