No relationship between schizophrenic birth and influenza epidemics in Japan

The finding that influenza epidemics are associated with an increased risk of adult schizophrenia has been controversial. Data was obtained from Japan's governmental statistics, the Patient Survey. Index years were defined as 1957/1958, 1962, and 1965, and comparison years were defined 2 years before and 2 years after the index year. Subjects were patients with schizophrenia who were born in the index years of influenza epidemics. Periods 5 months after the influenza epidemics were defined as exposed months. Proportions of patients born during the exposed period in the index years were compared with those of patients born in the corresponding months in the comparison years. The proportions of patients born in the exposed months in the index years were not significantly different from those born in the corresponding months in the comparison years, with odds ratios around 1 in the whole country, the Kanto area, and the Shikoku/Kyushu area where a remarkable influenza epidemic was observed in 1957. No difference was observed in analyses stratified by sex. In Japan, there was no relationship between influenza epidemics and schizophrenic birth.