The rates are quite low
by thejet403 (2022-01-24 22:26:54)

In reply to: Question for COVID experts re: Myocarditis in kids  posted by wpkirish


Myocarditis in general has a wide spectrum of presentation. In the developed countries and in younger patients, it is most often due to a virus, though a lot of the pathogenesis is still not fully known.

Background rates in normal years is roughly 5-10 per 100,000 patients (though this varies based on age and gender). The CDC data shows that for ALL patients, the risk of myocarditis in any patient infected with COVID is about 15-20x higher rates than would be expected. This data is somewhat messy for pediatrics/young adults, but for those of us in pediatric cardiology, we often cite that it is about a 10x higher risk than normal....which is still quite low and unlikely. This number takes into account some other cardiac manifestations we have seen (namely an entity called MIS-C), that can be more severe.

The best data, though, comes from the Big Ten study (https://jamanetwork.com/journals/jamacardiology/fullarticle/2780548). This study found that of nearly 1600 Big Ten athletes across all institutions, the overall rate of myocarditis was 2.3% for those who had COVID. However, when we dig into the data, it is important to note that only 9 athletes (0.5%) had clinical signs of myocarditis and the other group had cardiac MRI findings that may support a diagnosis of myocarditis IN THE CORRECT CLINICAL SETTING (my emphasis). These sub-clinical detections were clustered to some universities instead of others and some of the abnormal findings can also sometimes be more prevalent incidental findings in athletes. Which led a lot of us to question if the true rate is really 2-3% (still seems high to us) and more likely 0.5%.

Long story short, without clinical findings suggestive of myocarditis, it is quite unlikely to have significant myocarditis simply after a mild, self-limited case of COVID. Further, return to play testing for patients with just mild is not driven by any evidence or data. Some pediatricians have been doing ECG testing, but this is a test with poor specificity and negative predictive value.