The decrease of Kawasaki syndrome during the second COVID-19 wave: a potential, unexpected effect of social distancing

Since September 2020, the Tuscan situation has deeply changed with a significant increase of SARS-CoV-2 positive cases. In the six-month period between November 2020 and April 2021, 14 PIMS-TS children were admitted to 5 Paediatric Units (incidence 2.3/month), 10 boys and 4 girls with a mean age of 9.6 years). The PIMS-TS incidence rate, adjusted for the 5,170 children hospitalised, resulted in 0.27% and represented 13.9 % of paediatric COVID-19-related hospital admissions in Tuscany. Conversely, the number of observed KS significantly reduced compared to the first six months of the COVASAKI survey: 3 cases, 0.5 incidence/month versus 11 cases, 1.8 incidence/month (p<0.03, RR 0.27, 95% CI0.0–0.92). Comparing the 2.7 incidence/month of the 165 diagnosed KS from 1 January 2015 to 31 January 2020, a statistically significant difference has been detected (p<0.0005, RR 0.24, 95% CI 0.07– 0.59). The same result has been found limiting the analysis to the 92 children with KS diagnosed during the same corresponding 6 months of the last 5 years: 3.0 versus 0.7 incidence/month (p<0.0002, RR 0.21, 95% CI 0.06–0.53)