Epidemiology of acute respiratory illness during an influenza outbreak in a nursing home. A prospective study.

We observed an influenza epidemic caused by influenza A/Arizona/82 (H3N2) in a nursing home during 1982 to 1983. A survey indicated that 59% of the residents were immunized before the outbreak. The outbreak was observed to begin in November, peak in February, and disappear in April. A significant level of herd immunity may have accounted for the slow progression through the nursing home. In addition, serologic evidence of concurrent infection with respiratory syncytial virus, parainfluenza virus, and Mycoplasma pneumoniae was present in many residents. Epidemics of influenza in a closed, partially immunized population in a nursing home may proceed at a slower rate than in an open, largely unimmunized community. By monitoring for infection with other respiratory agents, the complex nature of the outbreak in this nursing home became evident.