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Masking healthcare workers (HCW) and visitors was effective to reduce nosocomial (NOSO) influenza (I) during 2014/15 epidemic with reduced vaccine effectiveness


Vaccination of HCW against seasonal influenza (SI) is the cornerstone for the prevention of NOSO I. In countries where vaccination cannot be made mandatory by law, an alternative exists: HCWs’ obligation to be vaccinated (VAC) or to wear a mask during SI epidemics. This is the strategy (called “Zoning”) adopted by HUG since 2009. In Switzerland, in winters 2013/14 & 2014/15, SI had similar epidemic curves but vaccine effectiveness differed. In 2014/15, the trivalent vaccine did not cover the major circulating SI H3N2 strain.


We describe 2013/14 and 2014/15 SI epidemics and NOSO at HUG.


Suspected cases of SI (respiratory symptoms, fever with chills, muscular pain, or prostration) were screened using nasopharyngeal samples analyzed by RT-PCR. Cases were defined as NOSO when symptoms occurred >72 h after admission. Regular audits were performed to assess compliance with recommendations.


In winter 2013/14, 309 patients were positive for I, 147 of which (47.6%) were NOSO. Droplet precautions with single room isolation whenever possible were implemented for 261 patients (84.5%). Of 4459 HCW observed, 78.5% were VAC or wore a mask. In winter 2014/15, “Zoning” was implemented on 31/12/2014. Early Jan 2015, a large number of SI was documented with a high proportion of NOSO: 49.2% (92/187), in particular in internal medicine (19/28; 67.8%). At time of audit, 992/1262 (78.6%) HCW were VAC or wore a mask. Additional measures were implemented from 15th January to 20th March 2015: mandatory mask for HCW (even for VAC HCW) and visitors. Following this additional measure, 68/175 (38.8%) cases were NOSO at HUG, in particular 19/121 (15.7%) in internal medicine. Recommendations were followed by 2143/2769 (77.4%) HCWs and 430/685 (62.8%) visitors. Droplet precautions were implemented for 432/468 (92.3%) SI patients.


During the large 2014/15 epidemic with reduced SI vaccine effectiveness, mandatory mask wear for HCW and visitors was an effective measure to reduce NOSO I.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.

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Iten, A., Bonfillon, C., Boymond, S. et al. Masking healthcare workers (HCW) and visitors was effective to reduce nosocomial (NOSO) influenza (I) during 2014/15 epidemic with reduced vaccine effectiveness. Antimicrob Resist Infect Control 4 (Suppl 1), O61 (2015).

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