Editor's note: In November 2009, the researchers retracted the findings of this study.
Sept. 16, 2009 (San Francisco) -- If you're going to buy a face mask to protect yourself against H1N1 swine flu, you might want to invest in an N95 respirator mask.
So suggests a new study showing that ordinary disposable surgical masks did not protect health care workers from infection with the flu or other viral infections. N95 masks, on the other hand, offered significant protection against flu infection.
Since the average person is not exposed to as many bugs as health care workers, "surgical masks might be OK in the community setting. But N95 masks would be better," says study researcher Raina MacIntyre, MD, PhD, professor of infectious diseases epidemiology at the University of South Wales in Sydney, Australia.
While more expensive, N95 respirator masks fit more tightly around the mouth and nose than ordinary surgical masks. When fitted correctly, they filter out 95% of small particles, although this isn't easy to do in the home setting.
N95 masks should be the standard protection offered to health care workers, MacIntyre tells WebMD. "Surgical masks have no efficacy in the health care setting."
MacIntyre's study was presented at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy.
It comes on the heels of a recent Institute of Medicine report that recommends that health care workers should use N95 respirators that are individually fit-tested.
Comparing Face Masks
The new study involved 1,936 health care workers at 24 hospitals in Beijing. Most participants were randomly assigned to wear surgical masks, fit-tested N95 masks, or N95 masks that were not fit-tested.
"They wore the masks for every shift for four weeks during [last year's] cold and flu season," MacIntyre says.
There was also a comparison group composed of hospitals workers who had the option of wearing no masks or surgical masks. "In China, many workers find wearing no masks unacceptable, so we picked [the comparison group] from hospitals where masks are least likely to be used," she explains.
During the four weeks of the study, the researchers tracked how many people developed infectious diseases. Anyone with symptoms was tested for viral and bacterial pathogens.
Results showed that surgical masks are not effective against illness or infection, MacIntyre says.
N95 masks, on the other hand, were 56% effective against lab-confirmed respiratory viral infections and 75% protective against confirmed influenza. The fitted N95 masks didn't appear to provide more protection than unfitted N95 masks.
"We recommend fit testing," MacIntyre says. Fit testing is also required by OSHA (Occupational Safety and Health Administration).
Frank Lowy, MD, an infectious disease expert at Columbia University College of Physicians & Surgeons in New York, tells WebMD that "this is a nicely designed trial" confirming what many doctors believe: "Ordinary surgical masks are not that effective in preventing transmission of flu viruses."
Lowy adds that he agrees with recommendations to offer health care workers N95 masks.
N95 face masks cost $10 to $60 a box depending on the manufacturer and the model. Like surgical masks, they should be worn only once and then thrown away, according to the Institute of Medicine.