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

https://doi.org/10.1016/j.jhin.2013.11.009Get rights and content

Summary

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 Hôpital 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.

Introduction

Nosocomial influenza outbreaks have been described in acute and long-term hospital facilities.1, 2 Hospital outbreaks are usually reported during the annual peak of community influenza activity, when infected patients, healthcare workers (HCWs) or visitors serve as a source of infection.3, 4 Patients, visitors, as well as healthcare personnel are part of the transmission chain, facilitated by generally low vaccination coverage or vaccine failure.5, 6, 7 Hospital departments treating elderly patients with multiple underlying diseases are particularly affected by influenza outbreaks and excess mortality.2, 8, 9 Transmission of influenza occurs through aerosols, droplets or direct contact (e.g. hands, surfaces), and has been reported to affect widely separated departments, across different hospital floors.9, 10, 11 Previous outbreak reports show that a precise epidemiological description of contacts combined with genotyping and molecular phylogenetic analysis provides insight into routes of transmission.9, 11, 12, 13 This combination may lead to improved control of nosocomial influenza infections and outbreaks.

The Hôpital Edouard Herriot in Lyon experienced an outbreak of influenza A(H3N2) during the 2011/2012 influenza season affecting three different wards of the acute care geriatric department. The aim of this study was to analyse routes of transmission during the influenza outbreak among geriatric patients and HCWs with the help of molecular-based subtyping methods in order to implement adequate control measures during future influenza seasons.

Section snippets

Influenza diagnostics and study setting

As part of the virological diagnostic testing, as detailed elsewhere, all patients and HCWs of the acute care geriatric medical ward (64 beds) of Hôpital Edouard Herriot in Lyon were screened for influenza-like illness (ILI) occurrence during the peak of the influenza season 2011/2012, from 20th January to 6th April 2012.1 During this study period, research nurses contacted the geriatric units on a daily basis to search for HCWs and patients with ILI, defined as rectal or axillary temperature

Clinical information

A total of 66 patients and 57 HCWs were screened for influenza during the study period. From 19th February to 15th March 2012, 22 cases of influenza A(H3N2) were detected, affecting 16 patients and six HCWs (Table I), resulting in a cumulative incidence of 11% for HCWs and 24% for patients. The mean time from admission to onset of influenza symptoms was 23.2 days (SD: 24.1). Six patients had acquired the infection nosocomially at least 72 h after admission to the geriatric ward. Of those

Discussion

The analysis of all influenza cases during the peak 2011/2012 season and molecular characterization of strains confirms three distinct outbreaks on the three different sections of the geriatric department of the Hôpital Edouard Herriot. Only the combined epidemiological and molecular approach was able to distinguish multiple outbreaks, rather than one large outbreak across the department.

It has been shown that influenza strains causing hospital outbreaks are similar to those circulating in the

Acknowledgements

The authors would like to thank M. Valette, V. Escuret and the technical staff of the Influenza National Reference Centre of Southern France. We wish to acknowledge A. Jasir and S. Ethelberg for their contribution to critical review of the manuscript.

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