Vol. 302 No. 17, pp. 1839-1926, November 4, 2009
Surgical Mask vs N95 Respirator for Preventing Influenza Among Health Care Workers: A Randomized Trial
Mark Loeb, MD, MSc; Nancy Dafoe, RN; James Mahony, PhD; Michael John, MD; Alicia Sarabia, MD; Verne Glavin, MD; Richard Webby, PhD; Marek Smieja, MD; David J. D. Earn, PhD; Sylvia Chong, BSc; Ashley Webb, BS; Stephen D. Walter, PhD
Context Data about the effectiveness of the surgical mask compared with the N95 respirator for protecting health care workers against influenza are sparse. Given the likelihood that N95 respirators will be in short supply during a pandemic and not available in many countries, knowing the effectiveness of the surgical mask is of public health importance.
Objective To compare the surgical mask with the N95 respirator in protecting health care workers against influenza.
Design, Setting, and Participants Noninferiority randomized controlled trial of 446 nurses in emergency departments, medical units, and pediatric units in 8 tertiary care Ontario hospitals.
Intervention Assignment to either a fit-tested N95 respirator or a surgical mask when providing care to patients with febrile respiratory illness during the 2008-2009 influenza season.
Main Outcome Measures The primary outcome was laboratory-confirmed influenza measured by polymerase chain reaction or a 4-fold rise in hemagglutinin titers. Effectiveness of the surgical mask was assessed as noninferiority of the surgical mask compared with the N95 respirator. The criterion for noninferiority was met if the lower limit of the 95% confidence interval (CI) for the reduction in incidence (N95 respirator minus surgical group) was greater than –9%.
Results Between September 23, 2008, and December 8, 2008, 478 nurses were assessed for eligibility and 446 nurses were enrolled and randomly assigned the intervention; 225 were allocated to receive surgical masks and 221 to N95 respirators. Influenza infection occurred in 50 nurses (23.6%) in the surgical mask group and in 48 (22.9%) in the N95 respirator group (absolute risk difference, –0.73%; 95% CI, –8.8% to 7.3%; P = .86), the lower confidence limit being inside the noninferiority limit of –9%.
Conclusion Among nurses in Ontario tertiary care hospitals, use of a surgical mask compared with an N95 respirator resulted in noninferior rates of laboratory-confirmed influenza.
Trial Registration clinicaltrials.gov Identifier: NCT00756574
Author Affiliations: Departments of Pathology and Molecular Medicine (Drs Loeb, Mahony, and Smieja and Ms Dafoe), Medicine (Dr Loeb), Clinical Epidemiology and Biostatistics (Drs Loeb, Smieja, Earn, and Walter), and Mathematics and Statistics (Dr Earn), Michael G. DeGroote Institute for Infectious Disease Research (Drs Loeb, Mahony, Smieja, and Earn), McMaster University, Hamilton, Ontario, Canada; St Joseph’s Hospital Regional Virology Laboratory, Hamilton (Dr Mahony and Ms Chong); Departments of Pathology and Microbiology and Immunology, University of Western Ontario, London (Dr John); Department of Microbiology, Credit Valley Hospital, Mississauga, Ontario (Dr Sarabia); Joseph Brant Memorial Hospital, Burlington, Ontario (Dr Glavin); and World Health Organization Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds, St Judes Children’s Hospital, Memphis, Tennessee (Dr Webby and Ms Webb).