From Medscape Medical News
Laurie Barclay, MD
October 1, 2009 — Use of a surgical mask may not be inferior to the N95 respirator in halting influenza transmission in healthcare workers, according to the results of a noninferiority, randomized controlled trial published online October 1 and to be published in the November 4 print issue of the Journal of the American Medical Association.
"Data about the effectiveness of the surgical mask compared with the N95 respirator for protecting health care workers against influenza are sparse," write Mark Loeb, MD, MSc, from McMaster University in Hamilton, Ontario, Canada, and colleagues. "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."
The goal of this study was to compare the surgical mask with the N95 respirator in protecting healthcare workers from influenza infection.
At 8 tertiary-care Ontario hospitals during the 2008 to 2009 influenza season, 446 nurses in emergency departments, medical units, and pediatric units were randomly assigned to use either a fit-tested N95 respirator or a surgical mask when caring for patients with febrile respiratory illness. Laboratory-confirmed influenza, measured by polymerase chain reaction or a 4-fold rise in hemagglutinin titers, was the main study endpoint.
Surgical mask efficacy was defined as being noninferior to the N95 respirator, with noninferiority defined as the lower limit of the 95% confidence interval (CI) for the reduction in incidence (N95 respirator minus surgical group) greater than −9%.
Of 478 nurses evaluated for eligibility from September 23 to December 8, 2008, 446 nurses were enrolled and randomized, with 225 assigned to use surgical masks and 221 to use N95 respirators. In the surgical mask group, influenza infection occurred in 50 nurses (23.6%) compared with 48 (22.9%) in the N95 respirator group (absolute risk difference, −0.73%; 95% CI, −8.8% to 7.3%; P = .86, with the lower confidence limit being inside the noninferiority limit of −9%). Noninferiority of the surgical mask was also shown for influenza A (H1N1).
"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," the study authors write. "Our findings apply to routine care in the health care setting. They should not be generalized to settings where there is a high risk for aerosolization, such as intubation or bronchoscopy, where use of an N95 respirator would be prudent."
Study limitations include the inability to determine compliance for all participants, that audits were conducted only on medical and pediatric units and not in the emergency department, the inability to account for the effect of indirect contact, and the inability to determine whether participants acquired influenza from hospital or community exposure.
"In routine health care settings, particularly where the availability of N95 respirators is limited, surgical masks appear to be non-inferior to N95 respirators for protecting health care workers against influenza," the study authors conclude.
In an accompanying editorial, Arjun Srinivasan, MD, from the Centers for Disease Control and Prevention in Atlanta, Georgia, and Trish M. Perl, MD, MSc, from the School of Medicine and Bloomberg School of Public Health at Johns Hopkins University in Baltimore, Maryland, note that appropriately designed and worn N95 respirators protect wearers from small-particle exposure.
For most patient care, the World Health Organization and the Society for Healthcare Epidemiology of America recommend the use of surgical masks, whereas the Centers for Disease Control and Prevention and the Institute of Medicine recommend wearing N95 respirators when caring for patients infected with H1N1 influenza.
"That this study is, to our knowledge, the first and only published randomized trial assessing respiratory protection for preventing influenza transmission is a sad commentary on the state of research in this area," Dr. Srinivasan and Dr. Perl write. "Uncovering the truth and identifying the most appropriate way to protect health care personnel will require that other investigators build on this study. Ultimately, accumulating a body of evidence on this topic will provide much-needed answers."
They also stress the importance of other measures to prevent influenza transmission, including vaccination and hand hygiene.
"While the debate over the role of respiratory protection in preventing influenza transmission will continue, neither the ongoing discussion nor the need for more research should excuse anyone from failing to implement other measures that are known to protect patients and HCP from influenza," they conclude.
The Public Health Agency of Canada supported this study. The study authors and editorialists have disclosed no relevant financial relationships.
JAMA. Published online October 1, 2009. Study, Editorial
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