Saturday, March 26, 2011

Study: Longevity Of Viruses On PPEs




# 5449





PPEs – or personal protective equipment – are items worn by Health Care Workers (HCWs) when examining or caring for potentially contagious patients. They include masks, gloves, and gowns.


During the opening months of the 2009 pandemic, it became 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. 


This, as you might imagine, raised concerns among HCWs that this strategy of reusing masks could expose them, and their patients, to the virus.  That, and the decision to issue surgical masks instead of N95s, 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


Unfortunately, there are differing opinions and gaps in our scientific knowledge regarding the relative effectiveness of N95 vs. surgical masks (something I’ve covered often, including here, here, and here) and on how long a virus may remain viable on inanimate objects (like masks & gloves).


Inanimate objects that can transfer infectious agents are called fomites, and the CDC’s  (very) short answer on how long viruses can remain viable on these surfaces reads:


How long can human influenza viruses remain viable on inanimate items (such as books and doorknobs)?

Studies have shown that human influenza viruses generally can survive on surfaces for between 2 and 8 hours.


Today we’ve a new study that looks specifically at how long viruses may remain viable on PPEs. It appears in the Japanese journal Environmental Health and Preventative Medicine  (Hat tip Tetano on FluTrackers).


Essentially, researchers inoculated various fomites (masks, gloves, gowns, wooden and steel desktops) with laboratory grown H1N1, and then tested the surfaces after 1, 8, and 24 hrs for the presence of the virus (HA titer & 50% tissue culture infective dose (TCID50)/mL were measured).


Environmental Health and Preventive Medicine

Volume 15, Number 6, 344-349, DOI: 10.1007/s12199-010-0149-y

Maintenance of influenza virus infectivity on the surfaces of personal protective equipment and clothing used in healthcare settings

Hiroko Sakaguchi, Koji Wada, Jitsuo Kajioka, Mayumi Watanabe, Ryuichi Nakano, Tatsuko Hirose, Hiroshi Ohta and Yoshiharu Aizawa

ABSTRACT (Excerpt)


The HA titer of this influenza A virus did not decrease in any of the materials tested even after 24 h. The infectivity of influenza A virus measured by TCID50 was maintained for 8 h on the surface of all materials, with the exception of the rubber glove for which virus infectivity was maintained for 24 h.


Our results indicate that the replacement/renewal of personal protective equipment and clothing by healthcare professionals in cases of exposure to secretions and droplets containing viruses spread by patients is an appropriate procedure to prevent cross-infection.


TCID50 is the  amount of a pathogenic agent (in this case the H1N1 virus) required to infect 50% of cell cultures inoculated.


The results indicate that all surfaces tested harbored viable H1N1 viruses for at least 8 hours, with some surfaces infectious for more than 24 hours.


These test results extend the window of infectivity from fomites considerably beyond what has previously been reported.


The debate over the proper use of PPEs, and just how protective they really are, is a contentious one.


During a highly virulent disease outbreak, getting the science right (and applying it) could save a lot of lives.  We were very lucky that the CFR (case fatality ratio) of the 2009 pandemic was as low as it was. 


Last January the IOM (Institute of Medicine) released, through the National Academies Press, an extensive, 200+ page update on the use of PPEs (personal protective equipment) for healthcare workers when facing pandemic influenza and other viral respiratory illnesses.


The short version is, we need better science upon which to make decisions regarding the right kind of protection for HCWs.


While the entire 200 page pre-publication pdf can be downloaded for free, you can also view an executive summary and an abbreviated list of recommendations.



While this study from the EHPM won’t close the book on fomite transmission - it does add to our knowledge of the subject – and it shows us just how hearty influenza viruses can be, even outside of a host.


For more on the debate over PPEs you may wish to review:


Why Size Matters
Study: Aerosolized Transmission Of Influenza
NPI’s and Influenza
NEJM Perspective: Respiratory Protection For HCWs

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