Low seroprevalence of SARS-CoV-2 infection among healthcare workers of the largest children hospital in Milan during the pandemic wave

was the first region within a Western country to be severely hit by the spread of severe acute respiratory coronavirus virus 2 (SARS-CoV-2).The coronavirus disease 2019 (COVID-19) pandemic started officially in Italy on February 21, 2020, 1 although today it is recognized that the virus had been circulating unnoticed for at least a month prior to that date.2,3 Several nosocomial outbreaks occurred in the first phase of the epidemic, and healthcare workers (HCWs) were the most vulnerable cohort for COVID-19 due to frequent and close contact with COVID-19 patients without, at least in an initial phase, adhering to strict hygienic measures.We conducted a cross-sectional seroprevalence study among the HCWs of the largest pediatric hospital in Milan during the period of maximum epidemic activity, when Lombardy accounted for 37% of cases and 53% of deaths in the country.