Surgical masks and N95 respirators provide similar protection against influenza

A McMaster University study has found that surgical masks appear to be as good as N95 respirators in protecting health-care workers against influenza. The research, published online today in the Journal of the American Medical Association (JAMA), concluded that surgical masks have an estimated effectiveness within one per cent of N95 respirators, and are not associated with an increased rate of infection of influenza or other respiratory viruses.

The N95 respirator is a protective mask that filters out 95 per cent of airborne particles. Following the rise of the H1N1 flu virus, the Ontario Ministry of Health and Long-Term Care recommended the use of the device for all health-care workers caring for a patient with influenza-like illness.

"Given the likelihood that N95 respirators will be in short supply during a pandemic and unavailable in many countries, understanding the relative effectiveness of personal respiratory protective equipment is important," said Dr. Mark Loeb, the principal investigator of the study and a professor in the Michael G. DeGroote School of Medicine at McMaster University.

Few previous studies have compared the effectiveness of the N95 respirator and surgical mask, which is both less expensive and more widely available than its air-purifying counterpart.

Loeb led a team of researchers who enrolled 446 nurses in emergency departments, medical units and pediatric units at eight hospitals in Ontario during the 2008-09 flu season. The nurses were randomly assigned to two different groups – 225 received surgical masks and 221 received N95 respirators.

The nurses were asked to begin using the surgical mask or the N95 respirator when caring for patients with influenza-like illness at the beginning of the influenza season, which was defined as two or more consecutive isolations of influenza per week in each study region. In addition to the protective breathing equipment, the nurses wore gloves and gowns when entering the room of a patient with flu-like symptoms.

In both groups, less than a third of the nurses had received the flu vaccine.

Study participants were assessed for signs and symptoms of influenza twice weekly using an internet-based questionnaire. To assess household exposure, the participants also reported whether family members or roommates experienced flu-like symptoms.

If a symptom was reported by a participant, a nasal specimen was obtained and tested for the influenza and other respiratory viruses. Influenza infection occurred in 50 nurses (23.6 per cent) in the surgical mask group and in 48 (22.9 per cent) in the N95 respirator group.

The researchers concluded that in routine health-care settings, particularly where the availability of N95 respirators is limited, surgical masks are as effective in protecting against influenza.

"It's certainly good to know that the protective effect of a surgical mark appears to be, based on our data, similar to the N95," said Loeb, an infectious disease physician and microbiologist who is recognized nationally and internationally for his research on SARS, West Nile Virus and influenza.

"This is certainly valuable information for health-care workers in North America who are required to wear N95 masks, but also for those in countries where respirators may not be available."

Following the outbreak of SARS in 2003, the Ontario Ministry of Health and Long-Term Care mandated the use of surgical masks for all health-care workers providing care to or when within one metre of a patient with influenza-like illness.

In April 2009, the ministry upgraded its guidelines on personal protective equipment for health-care workers. It now recommends that N95 respirators be used by health-care workers when within two metres of caring for symptomatic patients.

Source: McMaster University