An influenza B epidemic among children in day-care.

An outbreak of influenza virus type B infections occurred in the Frank Porter Graham Day Care Center from February to April, 1974. During the epidemic there were 27 isolations of influenza B virus from 20 children. One half of these were obtained from children who were well at the time of culturing. Attack rates as determined by virus isolation and seroconversion for most age groups approximated the 40% rate for the entire population. Clinical and microbiological data from this study were compared to those obtained in the center during the same three months in 1973. Increases in the incidence of otitis media and temperatures over 38 C were seen during the 1974 study. Intensive continuous microbiological surveillance for bacteria, viruses, and mycoplasmas failed to reveal predominance of any other potential pathogen to account for these clinical findings. The analysis permitted by the nature of this study design in a day-care setting revealed several unexpected findings: high attack rates unrelated to age; common inapparent infections; and frequent association with otitis media.