New study does little to settle debate over their usefulness
Monday, August 3, 2009
MONDAY, Aug. 3 (HealthDay News) — Experts are still debating the usefulness of wearing surgical face masks to ward off the flu, and the results of a new study aren’t likely to clear up the confusion.
Researchers in Hong Kong found that wearing a surgical face mask along with copious hand washing can help keep transmission rates for the seasonal flu down, at least among members of the same household. But it’s unclear how much the mask adds to the already-proven benefit of good hand hygiene.
Plus, the strategies only worked when started within 36 hours of the patient developing symptoms.
"Our study shows that face masks are useful in households when one person has influenza, to prevent transmission to other household members," said study author Benjamin Cowling, an assistant professor at the School of Public Health, The University of Hong Kong. "We did not study the use of face masks in other circumstances, for example for individuals trying to protect themselves against infection in other community settings."
According to Artealia Gilliard, a spokeswoman for the U.S. Centers for Disease Control and Prevention, current guidelines are unlikely to change based on the results of this study alone.
Those guidelines do not recommend the use of face masks in general, but can be "considered" for caregivers and if a novel H1N1 virus (such as the swine flu) appears in the community, Gilliard said. But the first line of defense would be to avoid high-risk situations and avoid being a caregiver.
"The best thing is to still listen to your local health department," said Dr. Scott R. Lillibridge, assistant dean at the Texas A&M Health Science Center School of Rural Public Health in Houston and executive director of the National Center for Emergency Medical Preparedness and Response.
The CDC-funded study appears in the Aug. 4 issue of the Annals of Internal Medicine, as does another study finding that the antiviral medications Tamiflu (oseltamivir) and Relenza (zanamivir) are effective for preventing symptoms of the seasonal flu in healthy adults.
Hundreds of thousands of people around the world die each year from the seasonal flu. And the recently arrived swine flu circling the globe has made the task of finding ways to prevent infection more urgent. Many fear the swine flu pandemic, still causing only relatively mild illness, will become more virulent in the fall.
The face mask and hand hygiene study involved 407 people arriving at one of 45 clinics in Hong Kong with flu-like symptoms and who had laboratory-confirmed influenza A or B. Also involved were 794 household members from 259 households.
The patients and their household contacts were randomized into three groups: a control group that received "lifestyle education" only; instruction in hand hygiene methods such as hand washing with soap or alcohol hand rub; and surgical face masks with hand hygiene.
Combined face masks plus hand hygiene helped prevent the spread of the virus, but the benefit was small and only when precautions were started within 36 hours of symptoms appearing.
It’s clear that hand washing helps prevent spread of the flu, and CDC guidelines support the practice. It’s less clear how much masks matter.
And there are many variables in face masks these authors didn’t address, Lillibridge pointed out.
"There are a lot of issues about face masks that tend to increase their usefulness. One is training. The second is proper fitting. The third is a new generation of face masks which have fibers that are treated with anti-viral and anti-microbial particles that increase killing. Those three important issues weren’t properly factored in in this study," he said.
"In our study we used surgical masks, which should be available over the counter in drugstores," Cowling said. "Another less common type of mask is the N95-style respirator, which has a much tighter seal on the face and is only really recommended for use in health-care settings in some situations. These masks work best if they are fit-tested."
The authors of the second study reviewed all available research on Tamiflu and Relenza, and concluded that healthy adults who took the drugs for four weeks or longer were less likely to be stricken with symptoms of flu, although the drugs did not prevent people from actually becoming infected with the virus.
"They prevent the newly formed viruses from leaving the infected cells but they don’t prevent initial virus from getting into the body," said study author Dr. Nayer Khazeni, an instructor of medicine in the division of pulmonary and critical care medicine at Stanford University Medical Center.
The two drugs appeared to be equally effective, although patients taking Tamiflu experienced more nausea and vomiting, especially if given in higher-than-recommended doses.
Also, the authors noted, many groups have just never been studied in this context, including children under the age of 12, immune-compromised individuals and people who have received the nasal flu vaccine.
"Another finding was that all of the studies were sponsored by makers of the drugs, which is not surprising," Khazeni said. "They were good quality, but it’s always nice to see an independent evaluation."
Although governments have stockpiled these two drugs to use during a pandemic, it’s unclear what role the drugs play currently in the swine flu pandemic.
"It’s not clear if there’s a role for extended use of prophylactic medications," Khazeni said. "Some groups are targeted for extended-duration antiviral prophylaxis, such as high-risk groups and first-line health-care workers."
But these plans are for a more severe pandemic setting, she added.
Also, cases of seasonal flu and swine flu that are resistant to Tamiflu have been seen.
SOURCES: Benjamin Cowling, Ph.D., assistant professor, School of Public Health, The University of Hong Kong; Artealia Gilliard, spokeswoman, U.S. Centers for Disease Control and Prevention, Atlanta; Nayer Khazeni, M.D., instructor, medicine, division of pulmonary and critical care medicine, Stanford University Medical Center, Stanford, Calif.; Scott R. Lillibridge, M.D., assistant dean, Texas A&M Health Science Center School of Rural Public Health, Houston, and executive director, National Center for Emergency Medical Preparedness & Response; Aug. 4, 2009, Annals of Internal Medicine