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.