NEWS

October 1, 2009

Conflict emerges over value of handwashing as a preventive flu transmission measure

Canadian health care professionals should be more willing to tap the national stockpile of pandemic (H1N1) 2009 flu vaccine, says Canada's Chief Public Health Officer Dr. David Butler-Jones. "We're the ones that kill our patients."

Prominent microbiologist Dr. Donald Low argues that the Public Health Agency of Canada's hand hygiene recommendations "are not evidence-based."

Photo Credit: ©2009 Jupiterimages Corp.

There’s no evidence that good hand hygiene practices prevent influenza transmission, according to a Council of Canadian Academies report commissioned by the Public Health Agency of Canada.

But N95 particulate respirator-type masks are a proven “final layer of protection” against even the smallest viral particles of influenza, says the Influenza Transmission and the Role of Personal Protective Respiratory Equipment: An Assessment of the Evidence report prepared by an expert panel on influenza and personal protective respiratory equipment, chaired by Dr. Donald Low, microbiologist-in-chief at Mount Sinai Hospital in Toronto, Ontario (www.scienceadvice.ca/documents/(2007-12-19)_Influenza_PPRE_Final_Report.pdf).

Despite those 2007 findings, PHAC still recommends handwashing as the primary preventive measure against flu transmission. The agency also states on its website that there is no evidence that wearing masks “will prevent the spread of infection in the general population. Improper use of masks may in fact increase the risk of infection.”

Moreover, PHAC states in an email to CMAJ that “there is substantial evidence to support hand hygiene as a basic premise of infection prevention and control measures.” The agency also indicated that its hand hygiene recommendations are based on a combination of expert opinion and evidence, including a recent Cochrane Collaboration systematic review (BMJ 2009;339:b3675).

But the contradictory evidence and recommendations on preventive measures and other pandemic (H1N1) 2009 issues leaves Canadian doctors at a loss as to the best advice to provide patients, says College of Family Physicians of Canada President Dr. Sarah Kredentser.

“The average family physician is confused and that’s partly because there is a lot of conflicting evidence and things change day by day,” Kredentser says, adding that there’s a need for the experts to get the information right and then get it out quickly to family physicians. To that end, the College is now working with PHAC, the Canadian Medical Association and other bodies to craft a one-page influenza guideline for physicians to use in the community.

The absence of any kind of national guidelines or strategies “makes it tough for physicians in practice. In this kind of situation, physicians actually want to be told: What do I do? How do I triage patients? What steps do I take to keep the office open?” Kredentser says, adding that even providing vaccination advice to patients is problematic given the ongoing national controversy over an unpublished study that indicates that getting the seasonal flu vaccine may double the risk of contracting pandemic (H1N1) 2009.

According to the Council of Canadian Academies report, though, there’s no conflicting advice regarding handwashing or the use of N95 respirators.

Low argues that the PHAC’s hand hygiene recommendations “are not evidence-based.” Noting that research on influenza transmission is limited, he adds that in the absence of adequate evidence, recommendations are often just “expert opinion.”

Hand washing is based on practical, rather than scientific, considerations, he says. It is “a simple thing to do and it may protect you from some other illnesses.”

But current evidence shows that influenza is transmitted primarily at a short range of one to two metres by inhaling particles from an infected person (“inhalation transmission”), although the virus can survive on surfaces and, theoretically, transmission can occur from contaminated surfaces and hands (“contact transmission”), according to the report, which was crafted in 2007 by 13 senior academic and clinical physicians, nurses and one judge from across Canada. The expert panel, which examined 128 sources of evidence, was struck by the Council of Canadian Academies in response to a request from PHAC. The council was established in 2005 with a $30 million founding grant from the government of Canada to provide independent assessments of scientific issues for governments and other bodies.

Low explains that receptors for the virus are located farther back in the respiratory tract than those for rhinoviruses (colds). It is more difficult for viral particles to reach the pharynx, trachea, bronchi and alveoli — where influenza receptors are found — from a contaminated hand touched to the mouth or nose. The particles can more readily reach the sites if they are inhaled.

“Every time you talk, laugh, cough, sneeze, you’re generating particles that are coming out of your mouth that are various sizes,” Low says. Large “ballistic” particles over 100 microns fall to the ground. But smaller particles ranging from 0.1 to 100 microns stay in the air from seconds to days, depending on humidity, airflow and ultraviolet light. These particles can be inhaled deeply into the respiratory tract, with smaller ones capable of reaching the tracheobronchial and alveolar tissues.

In practice, studies show the greatest risk is within one metre, Low adds. “Whether someone is infectious will vary [with] the amount of virus. There’s a huge dilutional factor right away as soon as you get away from the person infected.”

Surgical masks — designed to protect patients from surgeons — provide some protection against contact and inhalation transmission, but allow air in the sides and do not meet an established standard, Low explains.

N95 masks, however, do meet the test. Created to protect workers in the construction industry from breathing in particulates and widely available in hardware stores, they must meet standards set by the US National Institute for Occupational Safety and Health. They fit tightly on the face and block particles as small as 0.1 micron.

While PHAC states on its website that it does not recommend that healthy people wear masks as they go about their daily lives, Low says N95 masks have a role in protecting the public. “If you had somebody at home with influenza, wearing an N95 mask would be very appropriate.”

Low also rejected PHAC’s assertion that improper mask use may increase the risk of infection. PHAC claims that “masks do not act as an effective barrier against disease when they are worn for extended periods of time. In addition, removing your mask incorrectly can spread virus to your hands and face.”

Low dismisses as unfounded concerns that were expressed during the severe acute respiratory syndrome outbreak that N95 masks could be compromised by extended wearing (more than 4 hours), handling or a heavy virus burden. “These are very well-made masks.”

The Council of Canadian Academies report found that there are no studies on handling of used masks. The few studies of particle release from filters indicated that the release was insignificant and “unlikely to be of concern,”
Canada’s Chief Public Health Officer, Dr. David Butler-Jones, states on PHAC’s website, though, that it can be easy to get a false sense of security from wearing the mask.”

Low counters: “I don’t know where the false sense of security would come from.”

PHAC currently disagrees with using N95 masks except in very specific circumstances. “For example, we only recommend the use of N-95s for healthcare workers who are doing aerosol-generating procedures (like intubation). This kind of procedure would only be done in a health care setting. For home care, we recommend that the sick person wear a mask if possible, and if the sick person cannot tolerate it, the caregiver may choose to wear a mask when in close contact with the sick person,” the agency stated in an email.

The agency’s Infection Control Expert Advisory Working Group, though, is now reviewing evidence about the efficacy of N95 masks.

PHAC also indicated that its public recommendations were developed “by reviewing current scientific evidence and working with public health experts in infection control and infectious diseases.” It used the  Council of Canadian Academies report on respiratory equipment in its recommendations for health care workers, contained in the Infection Control Annex of the Canadian Pandemic Plan.

— Carolyn Brown, Ottawa, Ont. and Wayne Kondro, CMAJ

DOI:10.1503/cmaj.109-3066