The study comprise a nationwide, voluntary, on-line survey of inflammatory syndromes in children for retrospective (since 4th March 2020) and prospective data collection. Our aim was to capture and describe multisystem inflammatory syndrome in children (MIS-C) in Poland.

The voluntary surveillance for retrospective (since 4th March) and prospective data collection was initiated under the National Consultant of Pediatrics auspices. Anonymized patient data from pediatric hospitals from all over the country are extracted from electronic and paper records and collected through online form developed for that purpose. Before the surveillance was launched, reporting clinicians underwent an online training, which included the current state of knowledge about multisystem inflammatory syndrome in children (MIS-C). Patient management is at the discretion of the relevant treating clinicians.

KD and aKD were defined following the American Heart Association (AHA) guidelines.

TSS was established based on modified criteria by the Centers for Disease Control and Prevention.

MAS was diagnosed based on the Paediatric Rheumatology International Trials Organization (PRINTO) criteria for MAS classification.

The definition of the inflammatory syndrome was based on the WHO MIS-C definition with the exclusion of SARS-CoV-2 confirmation.

For patients who met the inclusion criteria, demographic data, past medical history, data on COVID-19 exposure, clinical symptoms, physical examination findings, laboratory, imaging, and cardiologic tests results, treatment, and outcome data are collected.

All study definitions are defined in accordance to relevant guidelines and evaluated automatically with the use of a dedicated software.

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.

Children aged 0-18 years old hospitalized with inflammatory conditions