Study questions surgical mask recommendation

A study comparing the effectiveness of surgical masks with respirators has challenged long-held beliefs about infection control.

A UNSW research team drew from the data of two randomised controlled trials involving 3591 Chinese participants to test the efficacy of hospital infection control guidelines that recommend surgical masks for infections spread by droplets.

Research lead professor Raina MacIntyre said the evidence is now overwhelming that respirators do a better job of protecting against respiratory infection than surgical masks and added the evidence that supports surgical masks is very weak.

MacIntyre said even for infections spread by droplets the study showed that respirators protect better.

“This turns upside down the long-held beliefs on infection control,” MacIntyre said.

She said this is because it suggests transmission of infection cannot be neatly classified as large droplets versus airborne particles.

“Essentially, everything we do in hospitals in terms of infection control is based on some experiments that were done in the 1940s and 1950s, where people looked at droplets and airborne particles and so on.

“There was a theory that arose from those old experiments that if you sneeze or cough, those big droplets … don't hover in the air for a long period.

“Then you get the other kind of particles, which are airborne particles, which are much smaller, and you may not even be able to see them, but they hover in the air for hours.

Generally, guidelines recommend that health professionals use surgical masks to prevent infections spread by droplets but one of the major findings of the study was that even for infections that are presumed to be spread by the droplet mode, a respirator protected much better than a surgical mask.

“The guidelines are saying if it's droplet infection, a surgical mask is fine, but what we showed is that actually a surgical mask doesn't even protect against droplet infection.”

She said this means, in practice, infections cannot be easily categorised into droplet and airborne and added it's likely that infections believed to be spread by large droplets also have some airborne transmission.

“In that sense, it really challenges some very entrenched views on hospital infection control that have been around for close to a century now.”

McIntyre said the issue of putting infections in the boxes of airborne and droplet plays out in the approach to influenza.

“The common belief about influenza is that it's droplet-spread. There's already a whole body of research that shows that yes, influenza is spread by the big droplets, but it is also airborne.

"For example, there was a study in the US where they looked at the emergency department after a patient with flu had been in there, and they could isolate full influenza virus in the air, three hours after the patient had left the emergency department. That proved that you do get airborne transmission.”

The authors said this new study confirms and reinforces that respirators should be used to ensure health workers are protected at the frontline.

“It is time that guidelines reflect the available evidence and that safety of health workers is prioritised.”

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