Take Away: SARS-CoV-2 infection has been clearly linked to heart muscle injury in those with severe COVID-19 illness. However, at present, there is insufficient data to determine the impact of mild or asymptomatic COVID-19 on the hearts of previously healthy individuals.

The Claim: COVID-19 can wreck your heart, even if you haven’t had any symptoms.

The Evidence: Several articles, including this August 31st piece (1), have raised the alarm about dangerous effects of mild or even asymptomatic cases of COVID-19 on the heart of infected individuals.

In support of this argument, there have been numerous reports, some of which are cited in the article above, documenting severe heart inflammation (myocarditis) and injury (e.g. cardiomyopathy and/or heart failure) in patients with COVID-19. However, most of these documented cases were in individuals with severe cases of COVID-19. At present, the evidence for clinically significant heart injury (requiring treatment or special precautions) from mild or asymptomatic COVID-19, is much less clear, especially in those with no prior evidence of heart disease.

One recent study reported that 78% of patients from an unselected cohort (including patients with asymptomatic, mild, and severe cases) had evidence of myocarditis (via MRI or blood testing) following COVID-19 infection (2). This study clearly demonstrated the link between COVID-19 and myocarditis by examining tissue from biopsies of the heart (the gold standard definitive diagnosis of myocarditis) of patients with the most severe cases. The study went on to show that, on average, patients who were treated for COVID-19 at the hospital (presumably more severe cases) and patients who were treated at home (presumably asymptomatic to moderate cases) both had blood test levels or MRI findings suggesting elevated myocarditis compared to non-COVID-19 infected patients with similar health profiles.

A key limitation here is “average”. The study was not designed or powered to look for the rate of myocarditis in only previously healthy patients with mild or asymptomatic COVID-19. This study included asymptomatic patients in the analysis, but without knowing their prior health or comparing their findings to other healthy non-COVID patients, it is not possible to infer the risk of myocarditis to this population. To their credit, the authors of the study discuss this limitation in their conclusions.

Despite this, the study was widely covered as evidence that ”COVID-19 can wreck your heart, even if you haven’t had any symptoms.“ In order to answer that question, we need research looking selectively healthy patients with mild or asymptomatic COVID-19 as outlined above.

Until that research is conducted, we might look at COVID within the same context as a number of other well studied viruses, many of which generally cause mild illness, that have also been shown to lead to heart injury and inflammation (3).

Disclaimer: This content is not intended as a substitute for professional medical advice. Always seek the advice of a qualified health provider with any questions regarding a medical condition.

Sources:

1. https://www.scientificamerican.com/article/covid-19-can-wreck-your-heart-even-if-you-havent-had-any-symptoms/
2. https://jamanetwork.com/journals/jamacardiology/fullarticle/2768916
3. https://www.ahajournals.org/doi/full/10.1161/CIRCULATIONAHA.108.766022

Take away: People are infectious for only part of the time they test positive. The tests for COVID-19 were granted emergency status by the FDA so some debate concerning the most ideal number of cycles is to be expected. It is worth noting that the FDA has the disclaimer "Negative results do not preclude 2019-nCoV infection and should not be used as the sole basis for treatment or other patient management decisions. Negative results must be combined with clinical observations, patient history, and epidemiological information (2)."

The claim: Up to 90 percent of people diagnosed with coronavirus may not be carrying enough of it to infect anyone else

The evidence: Per Walsh et al. (1), SARS-CoV-2 virus (COVID-19) is most likely infectious if the number of PCR cycles is <24 and the symptom onset to test is <8 days. RT-PCR detects the RNA, not the infectious virus. Therefore, setting the cycle threshold at 37-40 cycles will most likely result in detecting some samples with virus which is not infectious. As the PCR tests were granted emergency use by the FDA (samples include 2-9), it is not surprising that some debate exists currently about where the cycle threshold should be. Thresholds need to be set and validated for dozens of PCR tests currently in use. If identifying only infectious individuals is the goal, a lower cycle number may be justified. If detection of as many cases as possible to get closer to the most accurate death rate is the goal, setting the cycle threshold at 37-40 makes sense. A lower threshold will result in fewer COVID-19 positive samples being identified. It is worth noting that the emergency use approval granted by the FDA includes the disclaimer that a negative test does not guarantee that a person is not infected with COVID-19. RNA degrades easily. If samples are not kept cold or properly processed, the virus can degrade and result in a false negative result.

Source: 1 https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa638/5842165

2 https://www.fda.gov/media/134922/download

3 https://www.fda.gov/media/138150/download

4 https://www.fda.gov/media/137120/download

5 https://www.fda.gov/media/136231/download

6 https://www.fda.gov/media/136472/download

7 https://www.fda.gov/media/139279/download

8 https://www.fda.gov/media/136314/download

9 https://www.fda.gov/media/140776/download