An epidemic of Reye syndrome associated with influenza A (H1N1) in Colorado

An unusual cluster of Reye syndrome was associated with an outbreak of influenza A (H1N1) infections in the state of Colorado. Two of the 16 affected children had had prior episodes of Reye syndrome following respiratory infections, and one had had transverse myelitis following varicella. A serologic study of patients treated at a children's hospital and serum specimens submitted to the state health department revealed that approximately 59% of children in Colorado had been infected with the H1N1 strain of influenza A over a two-year period. Based upon this serologic survey, the minimum and maximum rates of Reye syndrome associated with H1N1 infections were calculated to be 2.5 and 4.3 cases per 100,000 H1N1 infections, respectively. A retrospective analysis of admissions to four referral hospitals in Denver failed to reveal any unusual clustering of Reye syndrome with outbreaks of influenza A H3N2 infections during 1975-1978. The reason for an association between Reye syndrome and the H1N1 strain but not the H3N2 strains of influenza A remains unclear.