Thursday, June 16, 2011

PPEs & Transocular Influenza Transmission






Photo Credit PHIL (Public Health Image Library)



# 5633


Constant readers of this blog are aware that over the past several years we’ve seen many differing studies on the  effectiveness of different types of  PPEs (Personal Protective Equipment) in protecting against influenza.




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 glaringly obvious 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.


This, as you might imagine, raised concerns among health care workers and sparked protests across the country.


Nurses Protest Lack Of PPE’s
Report: Nurses File Complaint Over Lack Of PPE
California Nurses Association Statement On Lack Of PPE



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.


image image

N-95 Respirator         Surgical Facemask


But over the past two 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 few highlights 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. 


But the truth is, our knowledge of how influenza spreads, and what barriers work well to protect HCWs, is severely limited.


Which is why a few months back the IOM (Institute of Medicine) released, through the National Academies Press, an extensive, 200+ page update on the use of PPEs  that essentially calls for better science on which to base our decisions regarding the right kind of protection for HCWs.


While the requisite knowledge won’t come overnight, today we have an ingenious piece of research that appears in the current issue of the IDSA’s  Journal of Infectious Diseases


Not only does it compare the efficacy of surgical masks verses N95s, it  gives us important new perspectives on the importance of eye protection against the influenza virus.


First the link, then I’ll return with a brief summary of what they found.


Transocular Entry of Seasonal Influenza–Attenuated Virus Aerosols and the Efficacy of N95 Respirators, Surgical Masks, and Eye Protection in Humans

Werner E. Bischoff, Tanya Reid, Gregory B. Russell and Timothy R. Peters



Finding safe and ethical ways to test the effectiveness of PPEs against influenza – when exposing test subjects to a virus could endanger their health – has always been a challenge.

Instead, researchers at Wake Forrest chose to expose 28 volunteers (divided into six groups) for 20 minutes to an aerosolized LAIV (Live Attenuated Influenza Vaccine) in a special air-tight chamber.

The six groups were:


  1. No protective equipment
  2. Ocular exposure only
  3. Surgical mask only
  4. Surgical mask plus eye protection
  5. Fit-tested N-95 only
  6. Fit-tested N-95 plus eye protection



While the study size was small, and the type of virus limited to 2 influenza A strains and 1 influenza B strain (MedImmune’s 2009/10 seasonal Flumist), the study yielded some very interesting results.


Researchers detected flu virus in all 4 subjects in Group 1 (unprotected), and in 3 of 4 in Group 2 (Ocular Exposure only).


Somewhat surprisingly, nasal washes of subjects with ocular exposure only were positive for flu virus within 30 minutes, suggesting the virus made its way rapidly to the nasopharynx by way of the nasolacrimal duct.


Flu virus was detected in all 10 volunteers who wore surgical masks (groups 3 & 4), regardless of eye protection.


N95 wearers (group 5) fared somewhat better, with 3 of 5 testing positive for the virus.


The best result came from the wearing of eye protection and an N95 (group 6). 


Only 1 in 5 subjects wearing that combination of protection showed detectable levels of virus.



The authors conclude:


"The eyes could be an entry route for influenza, allowing viral particles easy and fast access to the upper respiratory tract.

The type of surgical mask tested was inferior to a fit-tested N95 respirator in preventing aerosol delivery; however, none of the tested barrier precautions provided complete protection, including a CDC-recommended fit-tested N95 respirator and the addition of eye protection.”


This study – like all laboratory research – is subject to certain limitations. The results, while compelling, aren’t definitive.


The size of the study – 28 test subjects –was fairly small, and the substitution of a live influenza virus with an LAIV could have potentially skewed the results.


More research will be needed to confirm these findings.


Meanwhile, conflicting opinions regarding the efficacy of various types of respiratory PPEs will likely continue while we await further studies.

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