A clinical, epidemiologic, serologic, and virologic study of influenza C virus infection.

During a study of influenza-like illness in employees in the Pediatric Clinic at UCLA Hospital and Clinics in late November 1978, an influenza C viral strain was recovered from one employee, one person had more than a fourfold hemagglutination inhibition antibody titer rise to influenza C, and one person had specific influenza C IgM antibody. A survey of 334 children and young adults noted a seropositivity rate to influenza C of 64% for children up to 5 years old; 96% for 6- to 10-year-olds; 100% for 11- to 15-year-olds; and 98% for those over 16 years old. The 64% seropositivity of those children 5 years old and younger indicates that infection with influenza C early in life is common. The increasing seropositivity rates with age suggest that circulation and reinfection with influenza C commonly occurs.