Table II.

Study definitions

Variables	Definition
SARS-CoV-2 infection	Respiratory: any 1 of the following reported or documented clinical features: cough, dyspnea, tachypnea, increased oxygen requirement, or imaging suggestive of pneumonia. MIS-C: aged <21 years, with fever for >24 h, laboratory markers of inflammation, multisystem organ involvement, positive for SARS-CoV-2 testing or exposure to a suspected or confirmed COVID-19 case within 4 weeks of symptom onset, and no plausible alternative diagnoses. Other: Patients who did not meet the criteria for either respiratory COVID-19 or MIS-C.
Excluded cases	Patients with incidental SARS-CoV-2 included those hospitalized for psychiatric diseases (n = 9), trauma (n = 7), cancer treatment (n = 2), gastrostomy tube malfunction (n = 1), skin and soft-tissue infection (n = 8), urinary tract infection (n = 3), bacteremia (n = 2), otorrhea (n = 1), and Epstein–Barr virus infection (n = 1).
Severe disease	Previous definitions for severe disease include any admission to the ICU, need for supplemental oxygen or invasive mechanical ventilation and, for MIS-C, vasopressor support.1,3,5 We defined severe disease as ≥48 h in the ICU. With the exception of 1 patient who was transferred on the day of admission, 1 patient who was chronically ventilator-dependent and discharged on hospital day 1, and 1 patient who died on the day of admission, this definition included all children who were ventilated during hospitalization and/or required vasopressors. There were 16 patients (6%) who were admitted to the ICU for <48 h and none of these required mechanical ventilation or vasopressors.
Multisystem organ involvement	Two or more of the following: •Cardiovascular: require vasopressors, elevated troponins, arrhythmia, abnormal echocardiogram •Renal: acute kidney injury, renal failure •Pulmonary: need for supplemental respiratory support above baseline •Hematologic: elevated d-dimer, thrombocytopenia, anemia for age, leukopenia, thrombotic event •Gastrointestinal: nausea/vomiting, abdominal pain, diarrhea, elevated bilirubin or liver function tests •Dermatologic: rash, oral mucosal changes, conjunctivitis, peripheral extremity changes •Neurologic: encephalopathy, aseptic meningitis, stroke •Musculoskeletal: arthralgias, arthritis, myalgia, myositis
Thrombocytopenia	Defined as platelets count of <150 000/μL
Anemia for age	Defined as hemoglobin <10 g/dL if age <1 y, otherwise hemoglobin <9 g/dL
Lymphopenia	Defined as an absolute lymphocyte count of <1200/μL
Acute respiratory distress syndrome	Based on the Berlin definition45 or a physician diagnosis
Acute kidney injury	Defined as: increase in serum creatinine to 1.5 times baseline/age-appropriate standard32
Carditis	Defined as patients with a physician-diagnosed myocarditis or cardiomyopathy
Shock	Defined as requiring vasopressors
Thrombotic event	Defined as patients with 1 of the following: deep vein thrombus, pulmonary embolus, intracranial thrombus, or atrial thrombus
Obesity	Defined as a body mass index or weight-for-age (if <2 years old) ≥95th percentile for age and sex
Other coexisting conditions	•Respiratory: asthma, oxygen or tracheostomy dependent •Neurologic: cerebral palsy or seizure disorder •Cardiovascular: congenital heart disease, arrhythmia or hypertension •Diabetes: type 1 or type 2 diabetes •Gastrointestinal: gastrostomy tube dependence, gastroesophageal reflux disease, or other gastrointestinal chronic illness
Immunosuppressed	Defined as patients with immunosuppressive conditions or actively receiving immunosuppressant drugs
History of smoking	Defined as self-reported history of smoking (cigarettes or marijuana) or vaping
Medical complexity	Any 1 of the following: multiple comorbidities that require multiple services, technology-dependence, medical fragility (eg, cancer, congenital heart disease), or severe disability (eg, intellectual disability).
COVID-19 exposure	Given the high incidence of COVID-19 infection in the Tri-State area during the study period, all patients who met criteria for MIS-C were considered exposed.
Fever	Defined as having subjective fever or measured temperature of ≥38.0°C by any method
Hypoxia	Defined as oxygen saturation <90%
Tachypnea for age	Refers to a presenting RR per minute above the 95th percentile for age33 as follows: age <1 mo and presenting RR > 60; age 1-12 mo presenting RR > 50; age 1-4 y presenting RR > 40; age 4-12 y presenting RR > 30; age >12 y presenting RR > 25
SES index	Using data from the American Community Survey (2014-2018), we calculated a socioeconomic score index based on patient home addresses as previously described and validated.31 The index includes data from each patient's home zip code using census-derived ZIP code tabulation areas and combines six variables to form a SES score for each geographic area. The variables are the percentage of (1) adults with less than a high school education; (2) families with income below the federal poverty level; (3) households receiving public assistance; (4) female-headed households with children; (5) male unemployment; and (6) median household income. These measures were standardized to a mean of 0 and a standard deviation of 1, with positive values associated with a greater socioeconomic status. The variables were then summed and re-standardized to a mean of 0 and a SD of 1.

RR, respiratory rate.