Surgical masks aren't adequate to protect people from becoming infected during an influenza pandemic, a panel of experts said in a report released yesterday.
The report, written for the Public Health Agency of Canada, suggested industrial respirators known as N95s would be needed to minimize the risk of transmission of flu.
"Surgical masks don't really fit the bill," said Donald Low, chair of the panel that brought together infection control specialists, nurses and occupational health and safety experts.
"Even if they have a good filtering capacity, inhalable [virus]particles -- because they're not affected by gravity -- will take the route of least resistance, which will be around the mask and through the gap that exists between the surgical mask and the face."
The panel was asked to advise the public health agency on one of the most contentious issues in influenza science -- how flu spreads.
The answer will be used to craft guidance for provinces and territories on what protective equipment they should consider stockpiling for health-care workers in a pandemic as well as advice for the public on how to reduce the risk of getting sick.
A senior official with the public health agency said the report is one piece of information the organization will use to update the recommendations on infection control in health-care delivery contained in one of the annexes of the Canadian pandemic influenza plan.
Other items that will factor into the mix when that advice is being updated include the cost and availability of N95 respirators, how money spent on more expensive respirators might otherwise be spent as well as whether there are any unintended negative consequences of using them, said Arlene King, the director-general of pandemic preparedness.
"There is a ream of other issues that need to be considered as we move forward with developing and finalizing and revising the guidelines," said Dr. King, who noted the current intention is to publish the updated guidelines in the spring.
An N95 respirator is roughly 10 times as expensive as a surgical mask.
The panel was asked to answer two questions: how and where seasonal and pandemic influenza are transmitted and what role N95 respirators and surgical masks could play in blocking transmission. It did not conduct or commission new research, but rather analyzed the available scientific literature.
That evidence is sparse, inconclusive and hotly debated, used by both sides in a polarized debate about whether flu viruses waft through the air over distances or are mostly spread in heavy droplets sneezed or coughed at closer range into the mucus membranes of uninfected people.
The debate has been reignited in the pages of major international medical journals over the past couple of years, with Toronto-based scientists Raymond Tellier of the Hospital for Sick Children and Michael Gardam of the University Health Network expressing opposing views.
Both were on the expert panel.
Still, the group managed to come to a consensus.
Dr. Low suggested the compromise involved reframing the issue to look at whether viruses small enough to be inhaled deep into the respiratory tract can be generated by a person sick with flu.
The panel concluded that was possible, though likely those viruses would travel through the air only a short distance -- within an estimated two metres.
"But it doesn't rule out the possibility that at short ranges, that these viruses can still cause disease," said Dr. Low, chief microbiologist at Toronto's Mount Sinai Hospital.
"They can still get into the respiratory tract."
If inhalation has to be considered as one of the routes of transmission of influenza, then properly fitted N95 respirators are the appropriate form of protection, the panel concluded.
That's because properly fitted respirators create a seal between the face and the device.
In August, the Ontario government announced it was buying 55 million N95 respirators for its emergency stockpile to protect front-line health-care workers in a medical emergency such as a flu pandemic or another SARS-like outbreak.
The expert panel's guidance doesn't pertain strictly to health-care settings, though the Canadian pandemic plan does not currently take a stand on whether the public ought to stock up on masks or respirators for use in a pandemic.
"We don't come out one way or the other with respect to the use of masks by the public," Dr. King said.
"But we understand that people may choose to wear masks during a pandemic."
Dr. Low said if he were asked to translate the expert panel's conclusions for the general public, he would suggest people caring for infected persons at home during a pandemic wear a N95 respirator.
"If you're on the streets, on a bus, going to work -- that's a different scenario. The type of contact is different, the risk is different," he said, noting the guidance is similar to the advice the Centers for Disease Control have issued in the United States.
"For where we are today in understanding this, I think that's a pretty good stance."