Concurrent summer influenza and pertussis outbreaks in a nursing home in Sydney, Australia

OBJECTIVE: To report on the investigation of a summer outbreak of acute respiratory illness among residents of a Sydney nursing home. DESIGN: An epidemiologic and microbiological investigation of the resident cohort at the time of the outbreak and medical record review 5 months later. SETTING: A nursing home located in Sydney, Australia, during February to July 1999. PATIENTS: The cohort of residents present in the nursing home at the time of the outbreak. INTERVENTIONS: Public health interventions included recommendations regarding hygiene, cohorting of residents and staff, closure to further admissions, and prompt reporting of illness; and virologic and serologic studies of residents. RESULTS: Of the 69 residents (mean age, 85.1 years), 35 fulfilled the case definition of acute respiratory illness. Influenza A infection was confirmed in 19 residents, and phylogenetic analysis of the resulting isolate, designated H3N2 A/Sydney/203/99, showed that it differed from strains isolated in eastern Australia during the same period. Serologic evidence of Bordetella infection was also found in 10 residents; however, stratified epidemiologic analysis pointed to influenza A as the cause of illness. CONCLUSIONS: The investigation revealed an unusual summer outbreak of influenza A concurrent with subclinical pertussis infection. Surveillance of acute respiratory illness in nursing homes throughout the year, rather than solely during epidemic periods, in combination with appropriate public health laboratory support, would allow initiation of a timely public health response to outbreaks of acute respiratory illness in this setting.