Routes of transmission during a nosocomial influenza A(H3N2) outbreak among geriatric patients and healthcare workers

Background: Influenza presents a life-threatening infection for hospitalized geriatric patients, who might be nosocomially infected via healthcare workers (HCWs), other patients or visitors. In the 2011/2012 influenza season an influenza A(H3N2) outbreak occurred in the geriatric department at the Hopital Edouard Herriot, Lyon. Aim: To clarify the transmission chain for this influenza A(H3N2) outbreak by sequence analysis and to identify preventive measures. Methods: Laboratory testing of patients with influenza-like illness in the acute care geriatric department revealed 22 cases of influenza between 19th February and 15th March 2012. Incidences for patients and HCWs were calculated and possible epidemiological links were analysed using a questionnaire. Neuraminidase and haemagglutinin genes of culture-positive samples and community influenza samples were sequenced and clustered to detect patients with identical viral strains. Findings: Sixteen patients and six HCWs were affected, resulting in an attack rate of 24% and 11% respectively. Six nosocomial infections were recorded. The sequence analysis confirmed three independent influenza clusters on three different sections of the geriatric ward. For at least two clusters, an HCW source was determined. Conclusion: Epidemiological and microbiological results confirm influenza transmission from HCWs to patients. A higher vaccination rate, isolation measures and better hand hygiene are recommended in order to prevent outbreaks in future influenza seasons. (C) 2014 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.