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Is my hospital workstation contaminated with SARS-CoV-2?
Here’s: #HowIreadThisPaper from @CDCgov's J of Emerging Inf Diseases on aerosol and surface distribution of the virus that causes COVID-19 in a hospital in Wuhan, China.
wwwnc.cdc.gov/eid/article/26…
#Tweetorial 🧵
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Study goal: systematically assess contamination of hospital environment w/ SARS-CoV-2. Areas studied were a COVID+ ICU and an isolation general ward (“GW”). Authors stated the ICU had 15 pts w/ “severe” dz, and GW had 24 pts w/ “milder” dz. No mention of mechanical ventilation
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SETTING
🔦HIGHLIGHT #1: the layout of their COVID+ care units is pictured here. Does this look like your hospital’s COVID+ units?
I suspect the answer is a strong no. Take a look. This will be important in applying any of their results to your own hospital.
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METHODS
They used 2 techniques for virus detection:
1) SURFACES: sterile premoistened swabs of various hard surfaces (floors, computer mice, trash cans, bed rails, air outlets) and softer surfaces (pt masks, PPE, shoes, air outlet filters).
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2) AIR: Air samples were collected by using a “SASS 2300 Wetted Wall Cyclone Sampler” at *300 L/min for of 30 min* 🌪️🌪️🌪️ positioned per the figure
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**Background: The avg person breathes about 6-10 L/min at rest, and 50-60 L/min during exertion (ww3.arb.ca.gov).
Over 30 min that ranges from 180-1800 L of air.
Healthcare workers probably operate at the lower end of that range during avg pt encounters
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🔦HIGHLIGHT #2: the actual *clinical* significance of finding virus RNA in 300 L/min x 30 min = 9000 L of air is unclear and is neither demonstrated nor referenced in the paper.
We should thus approach any positive air sample results with a healthy dose of skepticism.
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Virus detection was done by testing “samples for the open reading frame (ORF) 1ab and nucleoprotein (N) genes of SARS-CoV-2 by quantitative real-time PCR.”
Why important? Authors later say, “the results of the nucleic acid test do not indicate the amount of viable virus.”
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🔦HIGHLIGHT #3: The utility of this type of testing for virus RNA is potentially very limited, as what we really care about is VIABLE virus.
That being said, we might still be able to use WHERE they found SARS-CoV-2 RNA to help decide if our practices need to change.
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Now on to a selection of notable RESULTS:
In the COVID+ ICU, they found virus on:
-70% (7/10) of unit floor samples
-75% (6/8) of computer mice samples
-66.7% (8/12) of air outlet filter samples
-40% (2/5) of patient mask samples
-100% (3/3) of *pharmacy* floor samples
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Now, what are we to make of this?
Well first, these %’s include both “strong positives” (= both genes detected) and “weak positives” (= only 1 of the 2 genes detected).
Is virus detected by only 1 of the 2 genes viable? Or even significant in any way? Unclear.
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Transforming the ICU results to just show “strong” positives might be enlightening:
-60% (6/10) of unit floor samples
-50% (4/8) of computer mouse samples
-33.3% (4/12) of air outlet filter samples
-20% (1/5) of patient mask samples**
-100% (3/3) of *pharmacy* floor samples
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🔦😷HIGHLIGHT #4: the patient mask** result.
This, of all the numbers in this entire study, is most question-provoking.
Why did masks on patients with “severe disease” NOT test “strongly” positive for virus in 80% of samples?
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Their results are, however *quite compelling* that computer mice, floors (in clinical and peri-clinical areas), and shoe soles of HCWs are contaminated with the virus. 🖱️👟
We’ll discuss the implications of these findings shortly.
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Now on to the COVID+ general *isolation* ward:
-8.3% (1/11) of ward floor samples
-8.3% (1/11) of door knob samples
-20% (1/5) of computer mouse/keyboard samples
-0% (0/3) of HCW shoe sole samples
-18.2% (2/11) of patient mask samples
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These are the results counting only “strong” positives:
-0% (0/11) of ward floor samples
-0% (0/11) of doorknob samples
-0% (0/5) of computer mouse/keyboard samples
-0% (0/3) of HCW shoe sole samples
-0% (0/11) of patient mask samples**
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Again, highlighting the patient mask result:
0/11 samples were “strong” positives + only 2/11 were “weak” positives.
This is troubling, I’d argue, because an infected patient’s mask should, theoretically, be the MOST likely object to have virus on it.
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Theoretical explanations for such low #’s of positive mask tests:
(1) Test process is faulty (poor sensitivity ➡️false negatives)
(2) Pts not actually wearing masks
(3) Pts not shedding virus onto mask
These are NOT mutually exclusive, and each has signif implications.
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If (1) is true, then their testing UNDERESTIMATES true virus contamination.
If (2) is true, then we cannot infer any meaning from the mask test result.
If (3) is true, then we would expect to also see LOW positivity for all other samples from same area, which we do.
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DISCUSSION
To summarize where we’re at:
-The layout of their ICU and ward may be very different from yours
-They tested air & surfaces for viral RNA (not same as viable virus) in COVID+ units
-Air testing is of unclear significance due to their collection & testing methods
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-Surface testing is likely much more relevant
-Found ICU had MANY surfaces w/ viral RNA
-Found isolation ward had very FEW surfaces w/ viral RNA
-Accuracy of results in question due to very low positivity of patient mask, but may suggest UNDERestimate of true contamination
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CONCLUSION
Now to the big money questions:
Are the findings of this study compelling?
Practice changing?
Despite its apparent flaws, I would argue YES for both.
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💡 The study compellingly demonstrates the presence of SARS-CoV-2 viral RNA throughout the ICU environment, on surfaces it SHOULD NOT be found, and could only have arrived there on the hands or shoes of healthcare workers.
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💡 The study presents us with evidence that would warrant changing our systems of practice to minimize potential spread of SARS-CoV-2 between healthcare workers and from COVID+ to COVID-negative patients. But how?
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3 potential initial interventions:
-Aggressively reduce the need for HCWs to touch common surfaces like doors, chairs, etc in COVID+ units
-Prohibit shared computer workstations on COVID+ units
-Introduce human monitors on COVID+ units to call-out hand-hygiene noncompliance
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Bottom line:
This study compellingly demonstrates contamination with SARS-CoV-2 viral RNA in areas outside of patients’ rooms in a COVID+ ICU, including on surfaces frequently touched by healthcare workers.
(end)
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