The Tecumseh Study of Respiratory Illness. IX. Occurence of influenza in the community, 1966--1971.

The occurrence of types A and B influenza infections was determined by isolation and serology over six years among residents of Tecumseh, Michigan. By isolation, there was evidence of type A infection for a limited period during each year of the study; most rises in titer were detected during the periods of viral isolation, but some also occurred out of season. Outbreaks of type B infection were encountered three times during the six-year period and out of season infections were less frequently seen than with type A. Infection rates with type A were relatively flat over the age range, with high rates seen in infants and small children; in contrast, highest infection rates with type B were observed in the 5--14-year-olds. On examination of illness rates, it was found that some of the outbreaks wound have gone undetected if surveillance techniques for infection had not been in operation. Frequency of respiratory illness with activity restriction was taken as a guide to influenza virus activity during outbreaks; it was found that highest rates of such illnesses occurred among the 1--4-year-olds for type A outbreaks, and among the 5--9-year-olds during mixed or type B outbreaks.