April 29, 2003 -- The images of mask-covered men, women, and children have been linked with SARS (severe acute respiratory syndrome) since the outbreak began. Sales of the paper masks have soared in areas hardest hit by SARS as people try to protect themselves from an unknown enemy. But how much protection can a simple mask offer from SARS?
Despite their popularity in Asia, experts say standard surgical masks -- the inexpensive square masks that tie behind your head -- are probably more effective in preventing people with SARS from spreading the disease than protecting healthy people from becoming infected.
CDC director Julie Gerberding, MD, says surgical masks are useful in filtering out relatively large particles of moist materials that you cough up or sneeze, which reduces the likelihood of passing SARS to another person.
"That's the reason why we recommend that those masks be used for patients with SARS because it contains their secretions and prevents them from being disseminated in the environment," says Gerberding.
Infectious disease expert Jon Temte, MD, PhD, of the University of Wisconsin says the pictures of people in Beijing and Hong Kong wearing surgical masks remind him of the influenza pandemic of 1918.
"I remember looking at old photos from the 1918 influenza pandemic and seeing people wearing masks everywhere," says Temte. "But that was never shown to be effective for preventing the spread of influenza."
Temte says it's really to early to know whether masks are an effective way to protect against SARS. Researchers simply don't know enough about the virus and how it spreads.
"On the flip side, there is probably not a whole lot of harm in it," Temte tells WebMD. "Any sort of barrier will reduce likelihood of droplet transmission."
Health officials at the World Health Organization and CDC believe SARS is spread primarily by close contact with droplets from an infected person.
"So if we're looking at a viral transfer on the basis of coughing up small droplets, when that droplet travels the distance between the person and the unlucky recipient and lands on fertile ground, you have transmission," says Temte.
Wearing a mask may protect people from inhaling these droplets and becoming infected, but the masks usually don't fit snugly and can allow droplets to enter the mouth or nose from the edges of the mask.
Although droplet transmission through close, personal contact with an infected individual is believed to be the primary mode of transmission of SARS, health officials have not ruled out the possibility that tiny particles of the SARS coronavirus may also spread the disease through the air. If such transmission is possible, some of these tiny virus particles may pass through a simple surgical mask or enter through an air gap.
Surgical masks also provide no protection for the eyes, and some types of virus particles can enter the body through the eyes as well as the mouth and nose.
In addition, some types of coronaviruses are known to survive on objects for several hours, which means it's possible that person with SARS person could sneeze and infect an object like a door knob that is later touched by someone who then rubs their eyes, nose, or mouth and becomes infected in that manner.
For protecting people from SARS infection, the CDC recommends that healthcare providers who care for SARS patients wear a much more efficient mask known as an N95 respirator. This type of mask is certified by the National Institute of Occupational Safety and Health (NIOSH) as being effective at filtering out at least 95% of airborne particles of a particular size.
There are also N99 and N100 masks that are even more efficient, but N95 masks are considered the standard for preventing infection from most known viruses.
But for these masks to work, they must be properly fitted to make sure there are no gaps between the mask and the skin. The mask is made of a thicker material than regular surgical masks and, when properly fitted, does not allow air to flow outside the mask.
Gerberding says N95 masks are only recommended for healthcare workers caring for SARS patients because they are at greatest risk of becoming infected. In fact, the majority of initial SARS cases were among doctors, nurses, and medical students who cared for the first round of SARS patients and did not wear such protection. Since infection control measures such as wearing N95 masks were implemented, the rate of SARS spread to healthcare workers has been drastically reduced.
"We don't recommend N95 masks for the general public. We don't recommend N95 masks for patients," says Gerberding. "We are recommending surgical masks for patients if they're well enough to wear one, and we're using those N95 masks in the healthcare environment in hospitals where we've got sick patients most likely to be aerosolizing relatively high concentrations of infectious material."
To reduce the risk of SARS transmission in the general public, the CDC recommends following good hygiene practices, such as frequent hand washing and use of alcohol-based rubs, and avoiding areas where SARS is known to have been spread.
SOURCES: CDC telebriefing, April 22. World Health Organization. Jon Temte, MD, PhD, associate professor at the University of Wisconsin in the department of family medicine.