HAMILTON, Ontario, Canada—Surgical masks are nearly as effective as the bulkier, more expensive, less comfortable N95 respirators in protecting health care workers from influenza, according to a study slated to be published in the November 4 issue of the Journal of the American Medical Association.¹

“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,” report researchers led by Mark Loeb, MD, MSc, of McMaster University in Hamilton, Ontario, Canada.

In the randomized controlled trial of 446 nurses in 8 Ontario hospitals, influenza infection occurred in 23.6% of nurses in the surgical mask group and in 22.9% in the N95 respirator group; equating in an absolute risk difference of -0.73% and indicating non-inferiority of the surgical mask, the study authors conclude. Study nurses were asked to wear either the mask or respirator when caring for patients with febrile respiratory illness, and the primary outcome of the study was laboratory-confirmed influenza.

N95 Respirator

Et tu, swine flu?

Non-inferiority was demonstrated between the surgical mask group and the N95 respirator group for those nurses who had an increased level of the circulating pandemic 2009 H1N1 influenza strain, the study showed.

That said, “our findings apply to routine care in the health care setting [and] 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,” the study authors note. “ 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.”

In an accompanying editorial,² Arjun Srinivasan, MD, from the Centers for Disease Control and Prevention (CDC) in Atlanta and Trish M. Perl, MD, MSc, from the School of Medicine and Bloomberg School of Public Health and Johns Hopkins University in Baltimore point out that the H1N1 pandemic has revived debate about the role of respiratory protection in preventing the transmission of influenza to health care personnel.

But the debate has been hampered by a lack of clinical trials that look at the efficacy of surgical masks and N95 particulate respirators. “Uncovering the truth and identifying the most appropriate way to protect health care personnel will require that other investigators build on this study,” they write. “Ultimately, accumulating a body of evidence on this topic will provide much-needed answers.”

Standard Surgical Mask

Translating research into practice: get flu shot, wash hands, use masks or respirators

“The results of this new study are somewhat surprising,” says Gilbert Ross, MD, a rheumatologist and the executive director and medical director of the American Council on Science and Health in New York City. “We have been trained to believe that the fitted, N95 respirator masks had significant efficacy in protecting people from inhaling infectious airborne particles containing influenza virus. Conversely, practitioners believe—up until now—that the common surgical masks offer little such protection for uninfected people, although they are thought to be useful in containing infection from spreading from infected patients to those in their environment,” he tells MSKreport.com

“The new JAMA study seems to show that the routine use of surgical masks reduces the risk of influenza as well as do the N95 masks,” he says. “Further, the surgical-type masks are widely available and cheaper than the N95 masks, and the N95s are in short supply in some areas”

The N95 masks are most effective when worn continuously and well-fitted, they are difficult to wear with facial hair, and many wearers do not adhere to the guidelines due to the discomfort involved in wearing them continuously, he points out.

“If confirmed on future trials, this would be good news for all of us, in the event of a widespread epidemic of influenza with higher mortality rates than we've been seeing, since distributing surgical masks would be relatively easy,” he says. “It would be especially good news for those who are most vulnerable to complications of influenza: those with chronic heart and lung disease, pregnant women, and those with compromised immune systems such as chemotherapy patients and patients with chronic autoimmune diseases such as rheumatoid arthritis and lupus—including especially those on immunomodulating therapies.“

The most important advice for all this flu season is to get vaccinated, he says. “Whether the ‘old’ seasonal flu or the novel H1N1 variety now spreading, flu kills over 30,000 Americans each year—many of those could have been prevented with the vaccine.”

A related study in Annals of Internal Medicine³ found that good hygiene and facemasks also prevent household transmission of influenza virus when donned within 36 hours of index patient symptom onset. “These findings suggest that nonpharmaceutical interventions are important for mitigation of pandemic and interpandemic influenza,” study authors conclude.

References

1. Loeb M. Dafoe, N, Mahony J, et al. Surgical mask vs N95 respirator for preventing influenza among health care workers: a randomized trial. JAMA. 2009;302: doi:10.1001/jama.2009.1466.
2. Srinivasan A, Perl TM. Respiratory protection against influenza. JAMA. 2009;302: doi:10.1001/jama.2009.1494.
3. Cowling BJ, Chan KH, Fang VJ, et al. Facemasks and hand hygiene to prevent influenza transmission in households: a cluster randomized trial. Ann Int Med. 2009; 151:437-446.