Follow-up study of type C influenza outbreak in a children's home.

A follow-up study of type C influenza in a children's home was made where the first outbreak of type C influenza occurred in March, 1981. During the survey period of 2 years, 2 additional outbreaks occurred in April and October, 1982 and 4 cases of the secondary and 2 cases of the tertiary infections were serologically confirmed. All of the children exposed to the outbreaks, except 2 particular cases who were suffering from German measles, showed similar mild respiratory symptoms characterized by fever and long-lasting nasal discharge, irrespective of primary, secondary, and tertiary infections. No case of inapparent infection was observed. Incubation period was estimated to be not longer than 5 days and the period of virus shedding, to be longer than 22 days. Antibody response in the sera of patients to type C influenza virus was equally good after every infection, although it was not efficient to prevent the succeeding infection. Factors involved in the repeated infections of type C influenza were discussed.