[Outbreaks due to respiratory syncytial virus and influenzavirus A/H3N in institutionalized aged. Role of immunological status to influenza vaccine and possible implication of caregivers in the transmission]

Abstract

Objectives: Report of epidemiological, clinical and virological data collected from the prospective surveillance of febrile episodes observed in aged residents of a long-stay care unit of 33 beds, at the University Hospital of Saint-Etienne, during the 1997-1998 winter season.

Methods: Systematic collection of clinical and biological data from febrile patients (> or = 38 degrees C) on a form, including virological findings obtained from a nasal swab and paired serum specimens.

Results: From 38 patients (37 of them having been vaccinated against influenza in October 1997), 18 febrile episodes were recorded in 16 subjects, including 3 respiratory syncytial virus infections and a late-occurring outbreak (March 1998) of influenza due to a A/H3N2 strain (15 cases, 14 of them virologically confirmed). No death was noted after the influenza outbreak. In 8 of the 9 tested patients with influenza, "protective" titres of antibodies directed towards the hemagglutinin of the vaccinal strain were present by radial hemolysis test three months before the beginning of the outbreak. During the influenza outbreak, the attack rate of symptomatic infection was 45.5% in elderly and 47.5% in healthcare workers (mainly unvaccinated). The occurrence of the first cases in the latter suggests their possible role in the transmission of the virus to the aged.

Conclusion: This study underlines the epidemic circulation of multiple respiratory viruses during the same winter season in long-stay care facilities, the occurrence of clinical influenza infections in vaccinated patients exhibiting protective antibody titres and the role of unvaccinated healthcare workers in the propagation of influenza in institutionalised aged.