BACKGROUND AND PURPOSE:

• SARS-CoV-2 infection appears to be associated with increased risk of myocarditis
• In this CDC Weekly Report, Boehmer et al. (MMWR, 2021) assess the relationship between myocarditis and SARS-CoV-2 infection using a large, US-based database

METHODS:

• Patient-level cohort study
  • Premier Healthcare Database Special COVID-19 Release (Large hospital-based administrative database)
• Population
  • All patients in with ≥1 inpatient or hospital-based outpatient encounter
  • Discharge between March 2020 to January 2021
  • Exclusion: Vaccinated individuals
• Exposures
  • SARS-CoV-2 infection
• Study design
  • Risk of myocarditis was calculated overall and by subgroup (sex and age group)
• Primary outcome
  • Myocarditis encounters occurring during or after SARS-CoV-2 infection

RESULTS:

• 36,005,294 patients
  • COVID-19 diagnoses: 4% (1,452,773 patients)
  • Myocarditis diagnoses
    • With COVID-19: 0.146%
    • Without COVID-19: 0.009%
  • Overall myocarditis diagnoses with history of COVID-19: 41.7%
• In adjusted analyses, COVID-19 was significantly associated with increased risk for myocarditis
  • Adjusted risk ratio (RR) 15.7 (95% CI, 14.1 to 17.2)
• Adjusted myocarditis risk difference (RD) was small due to small number of myocarditis cases
  • aRD 0.126% (95% CI, 0.112 to 0.140)
• The adjusted risk of myocarditis was higher among males
  • Males: aRR 0.165% (95% CI, 0.146 to 0.183)
  • Females: aRR 0.100% (95% CI, 0.087 to 0.113)
• The risk of myocarditis was lowest for patients aged 25 to 39 years, and risk was higher among younger and older ages groups
  • Patients aged 16 to 24 and 25 to 39 years: aRR 7.0
  • Patients aged <16 years and ≥75 years: aRR >30.0

CONCLUSION:

• Risk was higher in males than in females
  • Risk varied by age group, with the youngest and oldest patients having the highest associated risk
• The results of this study corroborate a recent study from Israel that found that while mRNA COVID-19 vaccination is associated with an elevated risk for myocarditis (risk ratio = 3.24; 95% CI = 1.55–12.44), SARS-CoV-2 infection is a strong risk factor for myocarditis (risk ratio = 18.28, 95% CI = 3.95–25.12)
• The authors state

Myocarditis is uncommon among patients with and without COVID-19; however, COVID-19 is a strong and significant risk factor for myocarditis, with risk varying by age group

The findings in this report underscore the importance of implementing evidence-based COVID-19 prevention strategies, including vaccination, to reduce the public health impact of COVID-19 and its associated complications

Learn More – Primary Sources:

Association Between COVID-19 and Myocarditis Using Hospital-Based Administrative Data — United States, March 2020–January 2021

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