Thread by @DepthAnesthesia

Starting a rolling thread reviewing some of the literature on risks of respiratory virus transmission in the health care setting.

We must take care of ourselves so that we can take care of others.

#COVID19 #PPE #medtwitter

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A fair amount of the literature is from the SARS and MERS outbreaks. I think some of the lessons, especially pertaining to the unique risks to healthcare workers and PPE management, continue to apply.

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Data from SARS in 2003 suggested that nosocomial transmission accounted for 72% of cases in Toronto and 55% of probable cases in Taiwan.

Of the cases, 44% in Toronto and 18% in Taiwan were in healthcare workers.

ncbi.nlm.nih.gov/pmc/articles/P…

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Particular attention is now being placed on procedures deemed to be higher-risk including endotracheal intubation and various non-invasive ventilation strategies.

These are so-called "aerosol-generating" procedures.

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Here's a small retrospective cohort of an intensive care unit in which nine SARS patients were cared for by 122 "at-risk" healthcare workers.

Ten workers met criteria for clinical case definition of probable SARS related to the care.

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The study observed that nurses and physicians who directly participated in intubation had a significantly increased risk of subsequently developing SARS.

RR, 13.29; 95% CI, 2.99 to 59.04; p = 0.003

atsjournals.org/doi/full/10.11…

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What's striking is that these patients were known as being infected and were appropriately being cared for by staff in PPE and negative-pressure rooms.

Clearly, there are opportunities for transmission in the ICU that are not being identified.

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PPE seems to work, though, based on this case-control study of 72 hospital workers with SARS and 144 matched controls.

This population was not in the ICU but rather on an inpatient ward.

ncbi.nlm.nih.gov/pmc/articles/P…

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Inconsistent use of goggles, gowns, gloves, and caps was found to be associated with a higher risk for SARS infection.

Unadjusted odds ratio 2.42 to 20.54, p < 0.05

A notable finding was that N95 versus surgical mask usage was not significant between controls and cases.

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Another interesting finding was that involvement in high-risk procedures was also not significant between controls and cases.

High-risk was deemed to include intubation, respiratory suctioning, cardiopulmonary resuscitation...

Odds ratio of 1.22 (0.45 to 3.14), p 0.8061

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With all that in mind, transmission of respiratory viruses still seems to be possible in spite of personal protective equipment.

This happened during cardiopulmonary resuscitation of a SARS patient.

ncbi.nlm.nih.gov/pmc/articles/P…

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ICU RN2 tested positive and was symptomatic. She assisted with IV insertion, medication administration, and application of EKG leads.

Her PPE included gown, gloves, safety glasses, face shield, shoe cover, hair cover, and N95 respirator.

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ICU RN1 tested indeterminate (?) and was symptomatic. She assisted with chest compressions.

Her PPE included all the PPE of ICU RN2.

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Notably, cumulative exposure time for both nurses was less than 15 minutes.

This case was interesting in that the patient was not conscious or breathing so the intubation was performed quickly and without difficulty.

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The authors postulate that either precautions were breached or an airborne viral load overwhelmed droplet precautions (either from chest compressions or bag-valve-mask ventilation).

One of the KEY TAKEAWAYS here is that the N95 respirators were NOT fit-tested.

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So, to clarify some of these conflicting findings on aerosol-generating procedures and transmission, here's a systemic review. Keep in mind that every single study is of VERY LOW quality.

ncbi.nlm.nih.gov/pmc/articles/P…

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The review observed that performing or being exposed to a tracheal intubation was the only "aerosol-generating procedure" most consistently associated with transmission.

The pooled OR was 6.6 (95% CI 4.1, 10.6) with high statistical heterogeneity (I2 = 61.4%)

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What we still don't know is whether transmission is happening from aerosols (airborne) or simply due to close-contact related to the actual procedure.

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Here's one more "super-seeding" type event in which 7 patients developed SARS after exposure to an undiagnosed patient.

Spoiler alert: another N95 that wasn't fit tested.

ncbi.nlm.nih.gov/pmc/articles/P…

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This is an excellent article on the ongoing controversy on airborne versus droplet and a diagram of all the potential transmission avenues.

ncbi.nlm.nih.gov/pubmed/31135389

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I hope that this content encourages healthcare professionals to use primary literature to guide not only our own knowledge but the knowledge we share with the public.

More importantly, I hope this reminds us about the importance of taking care of each other.

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@DrSandman11 @EmergMedDr @VatsalTrivediMD @jopo899 @sarahwollaston @MDaware @Surgeon_General @tim_elginnicu @sethdjudson @lianazucco @AbraarKaran

@reeprn @fitnurse @courtney_mdavis @aetiology @dockaurG @drsilenz @angie_ras @guscottj @vickymeig @amit_pawa @AllisonLeeNYC @atscommunity @andrewicu