Study shows surgical masks aren't protection
IH tenets upheld in N95, influenza research
Surgical masks provide virtually no protection against inhalation of airborne particles. Influenza involves airborne transmission as well as other forms of transmission.
Those are strong assertions that industrial hygienists have been making for many years, in support of more rigorous respiratory protection for health care workers. Now they can point to two new scientific studies that back them up.
In a study of elastomeric and N95 filtering-facepiece respirators and surgical masks, the surgical masks fared poorly, according to scientists with the National Institute for Occupational Safety and Health (NIOSH). The wearer would breathe in 53% of contaminated air, the researchers found.1 An N95 is designed to filter 90% of any air contaminant.
"Surgical masks don't provide much protection at all," says lead author Brent Lawrence, MS, an engineering technician at NIOSH in Morgantown, WV. "They don't have good fitting characteristics because they weren't designed to protect the wearer."
Elastomeric masks performed better than the N95 filtering-facepiece masks, but both were improved by fit-testing, the authors found.
Lawrence and his NIOSH colleagues tested 15 elastomeric N95 respirators, 15 N95 filtering-facepiece respirators, and six surgical masks. They found significant variation in the fit characteristics of the respirators and their performance with fit-testing.
When tested without fit-testing, only two of the N95 filtering-facepiece respirators typically used in hospitals had good inherent fit characteristics. Seven of the elastomeric respirators had good fit characteristics, while none of the surgical masks did.
The respirators varied widely in their fit-testing performance as well. Six of the N95 filtering-facepiece respirators failed to adequately fit anyone in the 25-person panel with at least one fit-test method. One filtering facepiece respirator, the MSA FR200 Affinity, failed all fit-tests. All of the elastomeric respirators had at least some successful fit-tests.
"From this study and previous studies we've done, [we found that] not all respirators are created equal. Fit-testing is an important component of protection," says Chris Coffey, PhD, chief of the laboratory research branch.
In the hospital setting, that could translate into a lot of frustration over fit-testing. In fact, the authors suggest that employers might find more success with quantitative fit-testing because more respirators failed the qualitative fit-tests.
"Instead of doing one quantitative test, you're doing two or three qualitative tests," says Coffey. "You're rejecting good-fitting respirators [because of fit-test errors]."
NIOSH is developing minimum criteria for the fit characteristics of filtering-facepiece respirators, called Total Inward Leakage. That would lead to less variation in respirator performance, Coffey says.
Other findings may reflect on respirator purchasing decisions. The elastomeric respirators had adjustable head straps, while some N95 filtering-facepiece respirators had only elastic, nonadjustable straps. "Adjustable straps may allow a more customized seal (i.e., having one strap tighter than the other strap) resulting in greater protection," the authors said.
Flu particles travel by air
Meanwhile, in a review of literature, Raymond Tellier, MD, MSc, FRCPC, CSPQ, a medical microbiologist at the Hospital for Sick Children in Toronto and associate professor at the University of Toronto, argues that there is plenty of evidence of airborne transmission of influenza — which would indicate the need for respiratory protection against pandemic influenza. The Centers for Disease Control and Prevention has recommended droplet and contact precautions against pandemic influenza — although that guidance is being revised.
Tellier notes that coughing and sneezing increase the number of particles that behave as aerosols, and that both animal and human experiments have demonstrated the infectivity of aerosolized influenza.
He also cites a study during the 1957-58 flu pandemic of a tuberculosis ward with ceiling-mounted UV lights meant to kill viruses in the upper air of the room and tuberculosis units without the lights. Although the same personnel treated the two groups of patients, and 18% of those health care workers contracted pandemic influenza, only 2% of the patients in the UV-irradiated rooms became infected with influenza. UV irradiation is not effective in inactivating viruses in fomites or droplet, he notes.2
"Despite extensive searches, I have not found a study that proves the notion that large-droplet transmission is predominant and that aerosol transmission is negligible (or nonexistent)," Tellier wrote.
While infection control practitioners argue that surgical masks have effectively stopped nosocomial influenza outbreaks, Tellier asserts that the evidence is actually "inconclusive." Lacking careful lab work, cases of influenza-like illness may be incorrectly attributed to influenza, and asymptomatic infections among health care workers are not counted. Immunity and vaccination also may have played a role, he says.
"Given the strong evidence for aerosol transmission of influenza viruses, in general, and the high lethality of the current strains of avian influenza A [H5N1], recommending the use of N95 respirators, not surgical masks, as part of the protective equipment seems rational," he concludes.
The CDC acknowledged that conclusion by changing its pandemic influenza guidance on respirator use. In that document, it states: "In contrast to tuberculosis, measles, and varicella, the pattern of disease spread for seasonal influenza does not suggest transmission across long distances (e.g., through ventilation systems); therefore, negative-pressure rooms are not needed for patients with seasonal influenza. However, localized airborne transmission may occur over short distances (i.e., 3 to 6 feet) via droplet nuclei or particles that are small enough to be inhaled. The relative contribution of short-range airborne transmission to influenza outbreaks is unknown."
IH position 'vindicated'
The two papers were welcomed by those who have pressed for adequate respiratory protection for health care workers, particularly in pandemic influenza planning.
"I'm very pleased to see that a lot of these issues are coming to the fore," says Gabor Lantos, MD, PEng, MBA, president of Occupational Health Management Services in Toronto. "It's been very political."
Lantos notes that surgical masks are not respiratory protection — even if they provide partial protection. "The epidemiology [infection control practitioners] keep quoting is based on the existing influenza strains, against which most everybody has partial immunity," he says.
Bill Borwegen, MPH, occupational safety and health director for Service Employees International Union (SEIU), says health care worker advocates feel vindicated in their insistence on better protection against infectious aerosols.
"We never understood how you could justify the use of a loose-fitting surgical mask to protect people from any kind of airborne biological agent," he says. "We know from the science that there's no such thing as a pure droplet spread."
The United States should now move forward to significantly increase its stockpile of N95 respirators, he says. "This is going to be the first line of protection and this is the weakest leg of a three-legged stool, [which includes antiviral medications and vaccines]," he says.
References
1. Lawrence RB, Duling MG, Calvert CA, et al. Comparison of performance of three different types of respiratory protection devices. J Occup Environ Hyg 2006; 3:465-474.
2. Tellier R. Review of aerosol transmission of influenza A virus. Emerg Infect Dis (serial on the Internet) October 2006. Available from www.cdc.gov/ncidod/EID/vol12no11/06-0426.htm.
If you had to, could you safely reuse N95s?
NIOSH seeks data with new respirator studies
What would you do if you run out of N95 filtering-facepiece respirators during a pandemic? So far, experts are advising against reusing the respirators — unless your alternative is to be unprotected.
But with a new study on respirator decontamination, the National Institute for Occupational Safety and Health (NIOSH) hopes to provide some better guidance. "We felt that there was an information gap," says Les Boord, director of the NIOSH National Personal Protective Technology Laboratory in Pittsburgh.
NIOSH will study the survivability of the influenza virus on a respirator surface and products or prototypes of respirators that incorporate antiviral technologies.
Meanwhile, NIOSH is studying other issues that may arise during a pandemic. For example, is it feasible to wear a surgical mask on top of a respirator to protect it from contamination? What is the physiological impact?
"When you put another device, such as a surgical mask on top of that, what does that do to the breathing resistance [within the respirator] and the carbon dioxide in the breathing zone?" says Boord. "It may be that the end result is an increased breathing resistance. Whether it's significant or not, we don't know."
NIOSH also will look for evidence on the optimal period between fit-tests. Currently, the respiratory protection standard of the U.S. Occupational Safety and Health Administration requires annual fit-testing for the N95 filtering-facepiece respirators.
Researchers will examine databases to see how many users needed to change respirators within a year of their prior fit-test, Boord says.
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