Table 4. New case definition for multisystem inflammatory syndrome in children of CSTE/CDC from January 1, 2023

Any illness in a person aged less than 21 years that meets:• The clinical AND the laboratory criteria (Confirmed), OR• The clinical criteria AND epidemiologic linkage criteria (Probable), OR• The vital records criteria (Suspect)

Clinical CriteriaAn illness characterized by all of the following, in the absence of a more likely alternative diagnosis1)• Subjective or documented fever (temperature ≥ 38.0℃)• Clinical severity requiring hospitalization or resulting in death• Evidence of systemic inflammation indicated by C-reactive protein ≥ 3.0 mg/dL (30 mg/L)• New onset manifestations in at least two of the following categories: 1. Cardiac involvement indicated by:  · Left ventricular ejection fraction < 55% OR  · Coronary artery dilatation, aneurysm, or ectasia, OR  · Troponin elevated above laboratory normal range, or indicated as elevated in a clinical note 2. Mucocutaneous involvement indicated by:  · Rash, OR  · Inflammation of the oral mucosa (e.g., mucosal erythema or swelling, drying or fissuring of the lips, strawberry tongue), OR  · Conjunctivitis or conjunctival injection (redness of the eyes), OR  · Extremity findings (e.g., erythema [redness] or edema [swelling] of the hands or feet) 3. Shock2) 4. Gastrointestinal involvement indicated by:  · Abdominal pain, OR  · Vomiting, OR  · Diarrhea 5. Hematologic involvement indicated by:  · Platelet count < 150,000 cells/μL, OR  · Absolute lymphocyte count (ALC) < 1,000 cells/μL

Laboratory Criteria for SARS-CoV-2 Infection• Detection of SARS-CoV-2 RNA in a clinical specimen3) up to 60 days prior to or during hospitalization, or in a post-mortem specimen using a diagnostic molecular amplification test (e.g., polymerase chain reaction [PCR]), OR• Detection of SARS-CoV-2 specific antigen in a clinical specimen3) up to 60 days prior to or during hospitalization, or in a post-mortem specimen, OR• Detection of SARS-CoV-2 specific antibodies4) in serum, plasma, or whole blood associated with current illness resulting in or during hospitalization

Epidemiologic Linkage CriteriaClose contact5) with a confirmed or probable case of COVID-19 disease in the 60 days prior to hospitalization

Vital Records CriteriaA person whose death certificate lists MIS-C or multisystem inflammatory syndrome as an underlying cause of death or a significant condition contributing to death

If documented by the clinical treatment team, a final diagnosis of Kawasaki Disease should be considered an alternative diagnosis. These cases should not be reported to national MIS-C surveillance.
Clinician documentation of shock meets this criterion.
Positive molecular or antigen results from self-administered testing using over-the-counter test kits meet laboratory criteria.
Includes a positive serology test regardless of COVID-19 vaccination status. Detection of anti-nucleocapsid antibody is indicative of SARS-CoV-2 infection, while anti-spike protein antibody may be induced either by COVID-19 vaccination or by SARS-CoV-2 infection.
Close contact is generally defined as being within 6 feet (about 183 cm) for at least 15 minutes (cumulative over a 24-hour period).