18. COVID-19: A Fishing Boat, Heart Damage, and What Low Oxygen Portends
Updated: Sep 7, 2020
A fishing boat out of Seattle gives a clue as to what COVID immunity looks like; an emergency department pulse ox study gives insight into the clinical course of patients discharged home who later develop low oxygen; and some staggering statistics on cardiac injury following COVID infection.
In this episode:
The difference between neutralizing antibodies and what’s tested for in the Abbott Architect commercial antibody test. The impact of neutralizing antibodies on immunity
Why some who have a positive commercial antibody test might not be immune
Sensitivity of RT-PCR testing and what a negative RT-PCR test means after a high risk exposure
A study from Johns Hopkins published May 2020 found: Over the 4 days of infection before the typical time of symptom onset (day 5), the probability of a false-negative result in an infected person decreases from 100% on day 1 to 67% on day 4. On the day of symptom onset, the median false-negative rate was 38% This decreased to 20% on day 8 (3 days after symptom onset) then began to increase again, from 21% on day 9 to 66% on day 21
The authors conclude “When the pretest probability of infection is high, the posttest probability remains high even with a negative result. Furthermore, if testing is done immediately after exposure, the pretest probability is equal to the negative posttest probability, meaning that the test provides no additional information about the likelihood of infection.”
Holy crap! That is some frightneting news especially considering that the message given to many patients is your test is negative, all clear.
So for those of you advising patients who have a negative test, take this into consideration when advising their activity over the next few weeks.
An emergency department study found that patients who develop hypoxia after discharge home have an increased incidence of adverse outcome
The authors discharged patients with suspected COVID home with a pulse oximeter.
Patients had to have a pulse ox of 92% or more in the emergency department to be included with instructions to return for pulse ox under 92% or they felt like they needed more attention.
A drop in home oxygen less than < 92% was associated with increased need for hospitalization, increased risk of intensive care unit admission, acute respiratory distress syndrome, and septic shock.
This doesn’t mean that a pulse ox of over 92% is a free pass, there were still some who didn’t get hypoxic at home who ended up in the ICU, but it was way fewer than those who did have hypoxia. In this study, a low home oxygen saturation doe mean you were more likely do die, just get sicker.
Based on this, I think it's fair to say that one of the return criteria amongst many others like feeling worse, shortness of breath or what not, is if your sat drops below 92%
A recent study found a 70% incidence of cardiac injury in 100 recovered COVID patients
Looking at Cardiac MRIs in 100 randomly selected patients recovered from COVID, at least 2 weeks after up to many months after, the study authors found heart injury in 70 percent of patients. This was irrespective of preexisting conditions, severity and overall course of infection, or the presence of cardiac symptoms.
Most common was myocardial or heart inflammation detected in 60 patients recently recovered from COVID-19 (60%), and that was followed by regional scarring.
The authors say, most of the imaging points toward “ongoing pericarditis after COVID-19 infection”
Almost 20% of the patients studied were asymptomatic and even some of them had cardiac injury.
*Note. This paper has since had several corrections that are described HERE.
Addetia, Amin, et al. "Neutralizing antibodies correlate with protection from SARS-CoV-2 in humans during a fishery vessel outbreak with high attack rate." medRxiv (2020).News Story
What does the Abbott test really test for?
Kucirka, Lauren M., et al. "Variation in false-negative rate of reverse transcriptase polymerase chain reaction–based SARS-CoV-2 tests by time since exposure." Annals of Internal Medicine (2020).
Shah, Sonia, et al. "Novel use of home pulse oximetry monitoring in COVID‐19 patients discharged from the emergency department identifies need for hospitalization." Academic Emergency Medicine (2020). Full Text
Woloshin, Steven, Neeraj Patel, and Aaron S. Kesselheim. "False Negative Tests for SARS-CoV-2 Infection—Challenges and Implications." New England Journal of Medicine (2020).
West, Colin P., Victor M. Montori, and Priya Sampathkumar. "COVID-19 testing: the threat of false-negative results." Mayo Clinic Proceedings. Vol. 95. No. 6. Elsevier, 2020.
Puntmann, Valentina O., et al. "Outcomes of cardiovascular magnetic resonance imaging in patients recently recovered from coronavirus disease 2019 (COVID-19)." JAMA cardiology (2020).