Multi-system Inflammatory Syndrome in Children (MIS-C) is a new condition related to COVID-19, the study investigators are still learning about its causes, effects, and long-term impact. "Long-Term Outcomes after the Multisystem Inflammatory Syndrome In Children", the Coronavirus MUSIC Study, is a research study funded by NIH and the National Heart, Lung, and Blood Institute. The study investigators hope to enroll at least 900 young people with MIS-C at children's medical centers in the U.S. and Canada. This research study will help us learn more about MIS-C and its effects on the long-term health of children.

This study is an observational cohort study that will use routinely collected clinical and cardiac (EKG, echocardiogram, Cardiac MRI, exercise testing) data to assess the association between MIS-C and cardiac outcomes within the first year after hospital discharge. Research funding will be available for EKGs, echocardiograms and MRIs in protocol windows that are not ordered by primary caregivers. The principal goal is to determine the spectrum and early time course of coronary artery involvement, LV systolic function, and arrhythmias or conduction system abnormalities, and, using these data, to define associated clinical and laboratory factors. The study investigators planned to include all eligible patients, including retrospective cases beginning January 1, 2020, with follow-up (in-person or telehealth) to up within one year and annual medical history forms until up to 5 years have elapsed since illness onset. Because many patients will have been identified by retrospective review, the study team will obtain consent at different times in their illness course. For this reason, it may be hard to reach some patients and their families. Waiver of consent will be obtained after three attempts have been made to locate the patient and family without success, as well as for the rare child who dies before informed consent can be obtained. The study investigators will include a HIPAA-compliant cryptographic algorithm to create a sharable "hashed" identifier from patient information. If blood work for research purposes is added on to usual clinically indicated blood work during follow-up visits, this will be covered by other informed consent forms.

Inclusion Criteria:

1. Age <21 years.
2. Fever ≥38°C for ≥24 hours, or report of subjective fever lasting ≥24 hours.
3. Laboratory evidence of inflammation, including, but not limited to, one or more of the following: an elevated CRP, ESR, fibrinogen, procalcitonin, d-dimer, ferritin, LDH, or IL-6, elevated neutrophils, reduced lymphocytes and low albumin.
4. Evidence of clinically severe illness requiring hospitalization, with multisystem (≥2) organ involvement, based on clinical judgment from record review, discharge diagnosis, laboratory or diagnostic tests. Organ system involvement includes but is not limited to cardiac, renal, respiratory, hematologic including coagulopathy, gastrointestinal including liver, dermatologic or neurological.
5. Positive for current or recent SARS-CoV-2 infection by RT-PCR, serology, or antigen test; or COVID-19 exposure within the 4 weeks prior to the onset of symptoms

Exclusion Criteria:

• No plausible alternative diagnosis, such as bacterial sepsis, murine typhus, staphylococcal or streptococcal shock syndromes

children and young adults <21 years with Multisystem Inflammatory Syndrome in Children associated with COVID-19 (MIS-C) at a participating hospital