Wednesday, March 08, 2006

Something about masks

One of the enduring images of the 1918 pandemic is of battalions of policemen wearing surgical masks. The mask issue is back in the news as the Institute of Medicine (IOM) continues its deliberations in preparation for a report due in the spring. IOM is the medical portion of the National Academies of Sciences (NAS), a prestigious honorary body of independent scientists who advise the government by request. The NAS is not just the National Academy of Science but the National Academies, being composed of the National Academy proper, the National Academy of Engineering, the Institute of Medicine and the National Research Council. Most NAS advisory activities are not done by the elected members but by NAS-sponsored committees of national experts on a subject that meet for a defined period of time and write a report. Committee members are not paid, they work hard and tackle some of the most difficult problems involving applications of science to policy. Controversial topics are often kicked over to the NAS or IOM so that the government agency or congress can get a hot potato off their plates. Some of the committees work nothing short of miracles. Some don't.

One of the questions facing this IOM-assembled committee involves the use of reusable masks in a flu pandemic. Some stockpilers and flu preppers have been laying in a supply of masks for almost a year and local governments, hospitals and the general public are now realizing there will be a shortage. One question is whether that will matter, because the efficacy of masks is still unknown. From the Committee charge:
Surgical masks are recommended for use in healthcare settings for routine patient care. National Institute for Occupational Safety and Health (NIOSH)-certified N95 particulate respirators are recommended for use during high-risk activities (e.g., aerosol generating procedures) in healthcare settings.

However, current disposable N95 respirators have a limited effective lifespan. Given the potential duration of a pandemic, which may constitute several waves of outbreaks, even stepped-up production of surgical masks and N95 respirators will be overwhelmed by the demand, especially if community use of masks is widespread.

Consequently, the Department of Health and Human Services has requested the Institute of Medicine of the National Academies to provide recommendations on two issues:
  • measures that can be taken that would permit the reuse of disposable N95 respirators in healthcare settings and

  • the need for reusable masks for the general public
With some exceptions, masks, gowns and gloves for use in patient care settings to protect patients and health care providers are one worker, one patient, one use. They are not designed to be washed or disinfected between uses or to be shared. The IOM committee is examining under what circumstances, if any, multiple uses would be recommended in a pandemic situation with severe shortages and whether their use by the general public is warranted. Good questions.
At a public meeting Monday, health experts [at the Committee's public hearing] cited a host of questions. Among them: how long the masks work once donned; whether reused masks could be contaminated and spread infection; how to ensure they're worn correctly _ N95 masks have to be fitted to the user's face and are hard to breathe in for long stretches.

And would wearing a mask on, say, the subway protect people enough, or should they have driven or stayed home? Linda Chiarello of the Centers for Disease Control and Prevention said if masks eventually are recommended for the public, the advice must not create a false sense of security.

"The lack of clear data ... is a dilemma for those of us on the front lines," said Dr. Jeff Durchin of the Seattle-King County Health Department, adding that people already call health departments to ask what masks they should personally stockpile.

"We should not be talking about the reusability of masks or other devices until we know whether they actually work to begin with," said Jeffrey Levi of Trust for America's Health, a nonprofit health advocacy group. (CBS News)
At an earlier meeting of the Committee a CDC visitor gave a PowerPoint presentation (available here) with that agency's current thinking. CDC assumes a bird flu pandemic would be transmitted from person to person as in seasonal flu, which they believe to be mainly from large-droplets of virus laden particles generated by coughs or sneezes. In this scenario, ordinary surgical masks would be useful to protect others from you, but of unknown and questionable value in protecting you from others.

CDC's recommendations are a combination of their Droplet Precaution and Airborne Disease Precaution categories for health care workers. These are Droplet Precautions, used for "large droplet" transmission diseases:
  • Face shield or goggles and a surgical mask (not N95) worn within 1 meter of a patient

  • Private room or room shared with other flu patients

  • Patient wears surgical mask outside of room
One of the open questions is whether flu virus is transmitted via droplet micronuclei, particles small enough to be respirable and to remain suspended in the air for long periods of time (the large droplets settle out quickly). The larger droplets from a cough or a sneeze can be reduced in size by evaporation in an astonishingly short span of time (seconds) but the relative importance of transmission by these aerosols is unknown. They require more stringent measures, called "airborne isolation (used, for example, for TB).
  • Negative pressure room with air exhausted to the outside

  • Fit tested, NIOSH certified particualte respirators (e.g., N95 masks) for personnel inside negaitve pressure room

  • Surgical masks for patients when outside of the room
Current recommendations for pandemic influenza combine these two levels of protection for health care workers:
  • Masks for close contact (Droplet Precautions)

  • Gloves (gowns if needed) for contact with respiratory secretions (Standard Precautions)

  • Hand hygiene (Standard Precaustions)

  • Additional protection during aerosol-generating procedures using N95 masks (e.g., intubation for mechanical ventilators, open suctioning, bronchoscopy); if a negative pressure room is avialbe for these procedures it is preferable.
Not everyone is happy about this compromise, in particular the unions representing health care workers.
The government plan to combat a flu pandemic aims to protect medical workers largely by having them use surgical masks that cost less than a quarter and lack federal approval as a shield against particles the size of viruses.

The decision, which officials at the Centers for Disease Control and Prevention say is only a first line of defense, is nonetheless drawing sharp criticism from labor unions and some public health experts.
Critics also question the CDC’s recommendation that, when in close contact with flu victims, health-care personnel wear disposable respirators - the lowest-grade mask that the government certifies as able to filter out toxins and germs.

Hospitals and CDC officials say it’s impractical to outfit doctors and nurses with more expensive and unwieldy respirators absent evidence that a virus will remain airborne and infectious for lengthy periods.
Labor unions and some health experts say the risks of disease and of a panic among workers are too great to rely on inexpensive masks, especially given research suggesting virus particles can remain active in the air for hours and can penetrate disposable masks.

"This is a program that will assure that health-care workers either get sick or decide not to show up for work because they don’t have adequate protection," said Bill Borwegen, health and safety director for the Service Employees International Union, which represents 875,000 medical employees.

Margaret Seminario, the AFL-CIO’s health and safety director, warned that the CDC is "laying the seeds for a further disaster" by failing to recommend more protective respirators for front-line responders. (Columbia Tribune)
Needless to say, this is still a matter of controversy.

Many people are not waiting for the IOM to settle the question and are buying their own N95 masks (the "N" stands for "not resistant to oil" and the "95" for the supposed efficiency at filtering out particles of 1 - 5 microns or larger, much larger than the .1 micron size of the virus). One thing we do know is that their use by health care workers in the SARS outbreak did not fully protect (from a recent paper in the Chinese Medical Journal [Chin Med J 2005;118(1):62-68]; citation numbers deleted):
Governmental agencies and literature reports recommend that a N95 half mask respirator be used to protect HCW[Health Care Workers] from SARS CoV. A number of studies reported that HCW became infected even when using this respirator along with other PPE (gloves, eye goggles, protective clothing). Since SARS CoV infection appears to result from contact with mucus membranes (e.g. conjunctival mucosa) a half mask respirator does not provide protection for all membranes (i.e. eyes). A N95 also has about 5% leakage through the filter and 10% around the mask. This can allow small particles and droplets to enter the mask even under ideal wearer conditions. One of the biggest problems for HCW that do use respirators is that they do not receive respirator training nor get fit tested, and are unlikely to perform fit checks every time they don their respirator. Failure to conduct these practices will increase potential exposure even when using a respirator.


Generally . . . studies report that surgical and paper masks are not effective in preventing SARS CoV. One study reported that surgical masks were effective, but others have not confirmed these results. It is also reported that N95 respirators do not provide the best protection against this virus. In the event that SARS CoV is only spread by aerosol [large] droplet and not by an airborne [microdroplet] route, it has been suggested that fit testing would not be that important and N95 would be effective. Such [microdroplet] spread is likely occurring as desiccated nuclei particles that are less than 1 μm in size. Based on the number of reports on the ineffectiveness of N95 respirators, it is suggested that some transmission occur by an airborne route. Even with SARS CoV being ineffectively transmitted by aerosol route, the lack of good protection from surgical, paper and N95 respirators/masks indicates that these would not be applicable for other emerging infective diseases. The N95 has been recommended for preventing exposure to tuberculosis and this is the origin of its basis for use in protection against SARS CoV [Revere note: and also influenza].
The issue of the adequacy of CDC recommendations came up in the bioterrorism debate over smallpox, as well. The International Association of Fire Fighters objected to the recommendation of N95 masks, asking for even more stringent requirements.

Suffice it to say nothing said here or by CDC or anywhere else is likely to stop people from wearing N95 face masks or stop vendors form selling them on the basis they will protect you and your family from influenza. Whether they will or won't, whether they can be reused or not, whether they will have other untoward side effects (interference with hearing, vision or breathing) remains to be seen.

For the record, the Reveres do not have any masks, since we doubt their effectiveness, but along with everyone else we are guessing.