A nationwide outbreak of Reye's Syndrome. Its epidemiologic relationship of influenza B.

Between December 15 and June 30, 1974, 379 cases of confirmed Reye's syndrome were reported to the Center for Disease Control. Of these, 316 occurred during February and March 1974. A simultaneous surveillance system for influenza B indicated that this clustering of cases of Reye's syndrome correlated both temporally and geographically with influenza B outbreaks. The incidence of Reye's syndrome was higher in rural than in urban centers. Epidemiologically, two groups of cases of Reye's syndrome emerge: those which occur in older children (median age 11 years), cluster in time and geographic region, and are associated with antecedent influenza B infection; and those which occur sporadically thoughout the year, are isolated in occurrence, occur in younger children (median age 6 years), and are associated with a wide variety of antecedent viral illnesses.