Summer influenza outbreak in a home for the elderly: application of preventive measures

Influenza outbreaks occasionally occur in nursing homes (NHs) despite vaccination, but occurrence during summer is a rare event. We describe an influenza outbreak during a heatwave in 2005, and discuss the usefulness of rapid diagnosis in facilitating early intervention as well as appropriate infection control measures. An outbreak was observed in a single NH with 81 residents (mean age 88 years) and 48 healthcare workers (HCWs) and lasted seven days. Fever, cough and wheezing were reported as the main symptoms in 32 affected residents (39.5%) and 6 (12.5%) HCWs. Influenza was suspected and provisionally confirmed by a rapid diagnostic test performed on specimens from four patients. The outbreak was further confirmed by culture and reverse transcriptase-polymerase chain reaction in seven out of 10 residents. The strain was similar to the winter epidemic strain of the 2004-2005 season: H3N2A/New York/55/2004. As soon as the outbreak was confirmed, a crisis management team was set up with representatives of the local health authority and NH staff. A package of measures was implemented to control the outbreak, including patient isolation and the wearing of surgical masks by all residents and staff. A therapeutic course of oseltamivir was prescibed to 19/32 symptomatic patients and to 5/6 HCWs, and 47 residents and 42 remaining HCWs received a prophylactic post-exposure regimen. The outbreak ended within 48 h. Case fatality rate was 15.6% among residents. Pre-outbreak influenza vaccine coverage among the residents was 93.5% and 41.7% in HCWs. The rapid diagnostic test enabled prompt action to be taken, which facilitated infection control measures.