| Demographic criteria | | |
| 1. Children and adolescents aged <19 years | Children and adolescents with KD | 5-year-old boy |
| 2. Documented or subjective fever (≥ 38.0 ℃) for >24 hours | Fever unresponsive to initial IVIG therapy | Prolonged fever (for 5 days) |
| 3. Clinical severity requiring hospitalization or resulting in death | Hospital stays longer than typical KD | ICU management |
| Clinical and laboratory criteria | (In KDSS) | |
| 4. Systemic inflammation: CRP ≥ 3.0 mg/dL (normal < 0.5) | CRP ≥ 7.0 mg/dL (92%) | CRP 6.7 mg/dL |
| 5. Organ dysfunction: ≥ 2 of 5 categories | Multi-organ dysfunction in most cases | Met 3 of 5 categories |
| ① Shock: clinician documentation in medical records | Shock (100%) | Shock with vasoactive drugs |
| ② Cardiovascular: EF < 55%, CAAs, or Tn elevation | EF < 50% (45%) and CAAs (73%) | Myocarditis (EF 45%) and CAAs (Z score 2.3) |
| ③ Hematologic: platelet count < 150,000 /μL or ALC < 1,000 /μL | Thrombocytopenia (80%) | – |
| ④ Gastrointestinal: abdominal pain, vomiting, or diarrhea | Abdominal pain (43%) and vomiting (59%) | – |
| ⑤ Mucocutaneous: KD-like features | Mucocutaneous (77%) | Complete KD (5 of 5 clinical features) |
| Microbiological criteria | | |
| 6. Evidence of SARS-CoV-2 infection within 60 days | | |
| ① Detection of SARS-CoV-2 RNA (i.e., PCR) or specific Ag/Ab | Co-existing infections in 1/3 of KD cases | SARS-CoV-2 Ab 164 U/L (normal < 1.0) |
| ② Close contact with a confirmed or probable COVID-19 case | For example, EBV- or IFV-associated KD | – |
| 7. Absence of a more likely alternative diagnosis | | No significant pathogens in laboratory tests |