Acute respiratory disease associated with influenza epidemics in Houston, 1981-1983.

Virological surveillance at "sentinel" clinics in Houston has demonstrated that the annual peak in the number of visits for acute respiratory disease (ARD) always coincides with the peak of influenza virus activity. A survey of visits to a health maintenance organization between 1981 and 1983 allowed us to calculate the age-specific rates of visits for ARD during two moderately severe influenza epidemics (1981-1982 and 1982-1983). During the most intense period of influenza virus activity the rate of visits for ARD was about 12 per 100 persons; the risk of developing ARD was greatest for preschool children (1981-1982, 27 per 100; 1982-1983, 29 per 100) and averaged about 10 per 100 for persons greater than 10 years of age. The risk of hospitalization with ARD was about 10 per 10,000 persons for residents of Harris County (Texas) during the same epidemics and was greatest for persons greater than 65 years of age.