Photo Credit PHIL (Public Health Image Library)
# 6253
We’ve a new study, appearing yesterday in the journal Clinical Infectious Diseases, that once again raises questions over the effectiveness of different types of PPEs (Personal Protective Equipment) used by Health Care Workers (HCWs) in an infectious environment.
Ideally, the well-protected HCW (Health Care Worker) working in an infectious environment would be wearing an N95 mask, gloves, gown and eye protection.
But during the opening months of the 2009 pandemic, it became apparent that our world faced a shortage of PPEs, and so strategies were adopted to maximize their use.
In some cases nurses were issued only one N95 mask to be used for an entire 8 hour shift, and told to don it only when in direct contact with a potentially infected patient.
In other venues, HCWs were issued surgical masks in lieu of N95s, despite the recommendation at the time from the CDC that N95 masks were the preferred level of protection.
Fortunately, the virulence of the novel 2009 H1N1 virus was less than originally feared. Had the pandemic carried a higher mortality and morbidity rate, the lack of PPEs would have become a much bigger issue.
For decades, the assumption was that only properly fitted N95 masks protected the wearer, and that surgical masks were only worn by HCWs to protect the patient during invasive procedures.
N-95 Respirator Surgical mask
But in recent years we’ve seen dueling studies that alternately show surgical masks to be a reasonable protective barrier against respiratory viruses . . . or pretty much useless.
Take your pick.
A brief tour of these conflicting reports include:
In October of 2009 the NEJM published a perspective article (see NEJM Perspective: Respiratory Protection For HCWs) based on a 2009 IOM evaluation of surgical masks vs. respirators, and came out in favor of the N95.
A few days later JAMA (Journal of the American Medical Association) published a study which reported that HCWs using surgical masks experienced `noninferior rates of laboratory-confirmed influenza’.
In March of 2010, we saw the following study (see Study: Efficacy of Facemasks Vs. Respirators) in Clinical Infectious Diseases, that suggested that surgical masks are just as effective as respirators in protecting HCWs.
In guidance, updated as late as March of 2010, the CDC continued to recommend N95 respirators for HCWs who came in close contact with suspected or confirmed influenza patients.
But in June of 2010, the CDC proposed new guidance that relaxed those recommendations to using surgical masks for routine care, and reserving N95 masks for aerosol producing procedures (intubation, suctioning, etc).
Still, the controversy remains.
Adding to the confusion, we’ve seen recent studies that give more credence to the notion that influenza may be spread in aerosolized form (see Study: Aerosolized Transmission Of Influenza), as opposed to primarily by large droplets, and may also be contracted via the transocular route.
Our knowledge of how influenza spreads, and what barriers work well to protect HCWs, remains limited.
All of which serves as prelude to this new study, that simulates the aerosolization of influenza viruses and measured the protective qualities of surgical masks and respirators by constructing a simulated exam room using `coughing and breathing manikins’.
Although the full paper is behind a pay wall, we can get a pretty good idea of the study’s content from the abstract.
Detection of Infectious Influenza Virus in Cough Aerosols Generated in a Simulated Patient Examination Room
John D. Noti, William G. Lindsley, Francoise M. Blachere, Gang Cao, Michael L. Kashon, Robert E. Thewlis, Cynthia M. McMillen, William P. King, Jonathan V. Szalajda, and Donald H. Beezhold
ABSTRACT (Excerpts)
Methods. National Institute for Occupational Safety and Health aerosol samplers collected size-fractionated aerosols for 60 minutes at the mouth of the breathing manikin, beside the mouth, and at 3 other locations in the room. Total recovered virus was quantitated by quantitative polymerase chain reaction and infectivity was determined by the viral plaque assay and an enhanced infectivity assay.
Results. Infectious influenza was recovered in all aerosol fractions (5.0% in >4 μm aerodynamic diameter, 75.5% in 1–4 μm, and 19.5% in <1 μm; n = 5). Tightly sealing a mask to the face blocked entry of 94.5% of total virus and 94.8% of infectious virus (n = 3). A tightly sealed respirator blocked 99.8% of total virus and 99.6% of infectious virus (n = 3). A poorly fitted respirator blocked 64.5% of total virus and 66.5% of infectious virus (n = 3). A mask documented to be loosely fitting by a PortaCount fit tester, to simulate how masks are worn by healthcare workers, blocked entry of 68.5% of total virus and 56.6% of infectious virus (n = 2).
Conclusions. These results support a role for aerosol transmission and represent the first reported laboratory study of the efficacy of masks and respirators in blocking inhalation of influenza in aerosols. The results indicate that a poorly fitted respirator performs no better than a loosely fitting mask.
The results here are fascinating.
First, this study provides more evidence of the role of aerosolized virus particles in the transmission of influenza. Important because these particles can stay aloft and viable for some time, and spread further than large droplets can.
From a more practical standpoint, the big revelation is that a surgical mask, as normally worn by HCWs, only blocked 56.6% of infectious virus particles.
But . . . if you tightly seal the surgical mask against the face , you can achieve a level of protection approaching that of a well fitted N95 respirator (94.8% versus 99.6%).
And a poorly fitted N-95 respirator provided little more protection (66.5%) than a loosely fitted surgical mask.
This study will no doubt add further fuel to the debate over what constitutes appropriate PPEs for healthcare workers during a pandemic.
For the rest of us, the takeaway message here is that surgical masks (which are much cheaper, and easier to stockpile) appear to provide a reasonable level of protection against aerosolized influenza viruses when tightly sealed against the face.
Which means, I suppose, that now I need to think about beefing up my supply of paper surgical tape.
