Inclusion Criteria:  patients who required hospitalization since 4th March 2020; diagnosed Kawasaki disease (KD) or incomplete (atypical) Kawasaki disease (aKD) or toxic shock syndrome (TSS) or macrophage activation syndrome (MAS) or unspecified inflammatory syndrome;  Exclusion Criteria:  other infectious and non-infectious causes that could be responsible for the disease  SARS-CoV-2 polymerase chain reaction (PCR) or serology result could have been positive or negative. Due to limited availability and reliability of serologic testing, proven or likely COVID-19 criterion was not a condition determining inclusion to the registry.