Sunday, July 14, 2013

The Great Mask Debate Revisited

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Photo Credit PHIL (Public Health Image Library)

 


# 7479

 

 

Fears over the MERS coronavirus (and avian flu), and the recent call by the Saudi government for pilgrims to wear face masks during Ramadan and the Hajj, will no doubt reawaken the debate over the appropriateness, effectiveness and logistics of mask wearing in public to prevent infection during a pandemic. 

 

As you’ll see, while it may seem like a no-brainer, there’s conflicting evidence of their effectiveness, the supply of face-masks is finite, and governments and public health agencies around the world are not all on the same page with their advice.

 

Our primary defense against any pandemic (until a vaccine can be developed and deployed) are called NPIs (non-pharmaceutical interventions).

NPI’s can be as simple as hand hygiene, covering your coughs, and avoiding crowds, or can involve the use of personal protective barriers like N95 or surgical masks, latex or vinyl gloves, and eye protection.

 

School closures, public education, staying home when sick, and engineered barriers to avoid exposure are also examples of NPIs.

 

There are two basic types of masks available to the public; surgical or medical masks and N95 respirators. Given the higher costs, and their likely limited supply during a pandemic or epidemic, N95 masks are less likely to be used by the general public.

 

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Surgical Facemask N-95 Respirator 

 

The simple surgical mask has the advantage of being cheap (a box of 50 is usually under $4), easy to don, and easier to breath through than the N95 respirator. Its role has traditionally been to protect others from the coughs or sneezes of someone who may be infected.

 

A 2008 NIOSH Science blog called Influenza Pandemic and the Protection of Healthcare Workers with Personal Protective Equipment describes their effectiveness thusly:

 

Medical masks are not designed or certified to protect the wearer from exposure to airborne hazards. They may offer some limited, as yet largely undefined, protection as a barrier to splashes and large droplets.

 

However, because of the loose-fitting design of medical masks and their lack of protective engineering, medical masks are not considered personal protective equipment.

 


This of course assumes a healthcare setting, where HCWs are in close, prolonged contact with probable or confirmed infected patients, and a higher standard of protection is required.

 

  • The evidence for the protective qualities of surgical masks is mixed, but in 2010 we looked at a study (see (see Efficacy of Facemasks Vs. Respirators), that suggests that inexpensive facemasks may be more effective than previously thought in protecting against the H1N1 virus.

 

  • And in 2009 (see JAMA: Surgical Masks vs N95 Respirators) we looked a report that HCWs using surgical masks experienced `noninferior rates of laboratory-confirmed influenza’. The implication here, according to the authors, is that surgical masks provide similar protection to N95 respirators in a routine health care setting.

 

Other studies have been less sanguine about the effectiveness of surgical masks to prevent infection in the wearer (see PPEs & Transocular Influenza Transmission), although they do appear to provide some degree of protection.  

 

Use of the N95 mask, which the CDC recommends for HCWs who may be exposed to the MERS coronavirus or H7N9 (along with gloves, gown, & eye protection – see CDC: Interim Infection Control Guidelines For MERS-CoV) would be somewhat problematic for the general public.

 

  • They are uncomfortable to wear for long periods of time. 
  • They saturate with exhaled moisture relatively quickly, and must be changed out every couple of hours. 
  • The must be fit tested for each wearer (see Survival Of The Fit-tested)
  • They are 10 times more expensive than surgical masks.
  • They are considered a `last line of defense’ by the CDC and are really only effective when combined with gloves, hand hygiene, and eye protection.   
  • They must be removed and disposed of properly, to avoid contamination
  • And lastly, our national supply of N-95s is likely inadequate to supply even our Health Care Workers during a prolonged severe pandemic wave.

 

The bottom line is that surgical masks (and N95 respirators) may be somewhat protective for the wearer, but they will be in short supply during a severe pandemic, and are certainly not guaranteed to protect the wearer.

 

Which is why the World Health Organization has been reluctant to recommend the wearing of masks by the general public (see WHO: MERS, Masks, And The Media and More From WHO on MERS & Masks).

 

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Credit @WHO June 13th, 2013

 

In Advice on the use of masks in the community setting in Influenza A (H1N1) outbreaks Interim guidance  - while not recommending the public use of masks - WHO doesn’t come out strongly against them, either. And should the threat from MERS change, WHO could very well adjust their recommendations down the line.

 

The HHS issued guidance in 2007, as part of their H5N1 and pandemic flu preparedness push, on the use of facemasks by the public during a pandemic.

 

 

Interim Public Health Guidance for the Use of Facemasks and Respirators in Non-Occupational Community Settings during an Influenza Pandemic

May 2007

This document describes interim guidance for the use of facemasks and respirators in certain public settings during an influenza pandemic. Very little information is available about the effectiveness of facemasks and respirators in controlling the spread of pandemic influenza in community settings. In the absence of scientific data, this document offers interim recommendations that are based on public health judgment and on the historical use of facemasks and respirators in other settings. In brief, these interim recommendations advise the following:

  • Whenever possible, rather than relying on the use of facemasks or respirators, close contact and crowded conditions should be avoided during an influenza pandemic.
  • Facemasks should be considered for use by individuals who enter crowded settings, both to protect their nose and mouth from other people's coughs and to reduce the wearers' likelihood of coughing on others.  The time spent in crowded settings should be as short as possible.
  • Respirators should be considered for use by individuals for whom close contact with an infectious person is unavoidable. This can include selected individuals who must take care of a sick person (e.g., family member with a respiratory infection) at home.

Facemasks and respirators should be used in combination with other preventive measures, such as hand hygiene and social distancing, to help reduce the risk for influenza infection during a pandemic. This interim guidance will be updated as new information becomes available.

(Continue . . . )

In 2008 (see The HHS Revised Mask Recommendations) new draft guidance for mask use by the public was released with even stronger recommendations, but that document appears to be no longer online. Although it wasn’t formally adopted, the interim advice offered by the HHS in 2008 still seems prudent to me:

 

Pandemic outbreaks in communities may last 6 to 12 weeks.[3]  Persons who cannot avoid commuting on public transit may choose to purchase 100 facemasks for use when going to and from work.  An additional supply of facemasks also could be purchased for other times when exposure in a crowded setting is unavoidable or for use by an ill person in the home when they come in close contact with others.[4]


The problem, of course, is supply.

 

Our Strategic National Stockpile contains more than 100 million  N95 and surgical masks (see Caught With Our Masks Down), but the demand for PPEs during a serious pandemic would far exceed the supply. 

 

At one time the HHS estimated the nation would need 30 billion masks (27 billion surgical, 5 Billion N95) to deal with a major pandemic (see Time Magazine A New Pandemic Fear: A Shortage of Surgical Masks).

 

Which means that if you intend to avail yourself of the (admittedly limited) protection of face masks during a pandemic, your best bet is to buy any supplies well before a pandemic erupts.

 

Another alternative (offered without recommendation) was published in the CDC’s Journal of Emerging Infectious Diseases back in 2006 (see The Man In The Ironed Mask); A homemade reusable mask made out of Tee-shirt material.

 

Emerging Infectious Diseases Volume 12, Number 6, June 2006

Simple Respiratory Mask

Virginia M. Dato, David Hostler & Michael E. Hahn

Figure. Prototype mask. A) Side view, B) Face side. This mask consisted of 1 outer layer (≈37 cm × 72 cm) rolled and cut as in panel B with 8 inner layers (<18 cm2) placed inside (against the face). The nose slit was first placed over the bridge of the nose, and the roll was tied below the back of the neck. The area around the nose was adjusted to eliminate any leakage. If the seal was not tight, it was adjusted by adding extra material under the roll between the cheek and nose or by pushing the rolled fabric above or below the cheekbone. Tie b was tied over the head. A cloth extension was added if tie b was too short. Finally, tie c was tied behind the head. The mask was then fit tested.

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Another study, which appeared in PLoS One  in 2008 (see What Everyone Will Be Wearing During The Next Pandemic Flu Season), found that homemade masks – while not as effective as N95s – could offer some degree of protection against viral infection.

 

Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population

Marianne van der Sande, Peter Teunis, Rob Sabel

 

Although I would certainly prefer the protection of an N95 mask (and eye protection), I’ve always believed that in an potentially infectious environment, any mask beats having no mask at all.

 

But as always, your mileage may vary.

4 comments:

Anonymous said...

how about respirators with
silicon-fit and removable filters

Michael Coston said...

I'm sure they could be used (with the appropriate filter) but they require disinfecting-decontamination between uses, keeping track of the `remaining life' of the filters, are far less comforatble to wear for long periods of time, and are difficult to communicate through.

All reasons why disposable N95s are routinely used in a hospital environment instead of full or half face `industrial' respirators.

Anonymous said...

and how about the CPAP masks ?
You can wear the filter on the hat.
It should be more comfortable, Apnoe-people sleep with it.

Michael Coston said...

Although I suppose a full face CPAP mask could be fitted with an N95 filter of some sort, the forehead support bar would probably make wearing eye-protection difficult.


Seems like an over-engineered solution to me.