Effects of external factors on admission rates
A relationship between lockdown measures during the pandemic (a complete working from home obligation and/or school closures) and admission numbers is observed and illustrated in Figure 2. It was found that when lockdown measures were most strict and schools were closed, the number of PICU admissions for SAA was the lowest, indicating an association between the two. After lockdown restrictions were lifted, the admission rate tended to increase. Most children (70.2%) showed signs of an airway infection as trigger for their SAA, and in 60.1% a viral test was taken (Table 1). Most often, the clinical diagnosis of a viral infection was not confirmed by a positive viral test, resulting in 38.7% of children being infected with an unknown virus. If confirmed, Rhinovirus (23.8%) was the most commonly detected virus, followed by Bocavirus (5.4%), and Enterovirus (4.2%) (Table S2). Finally, regarding environmental triggers, no relationship was found between the peak in the fall of 2021, and pollen or ambient PM2.5 concentrations (Fig S2). Moreover, no correlations were observed between the monthly PICU admission numbers and pollen or PM2.5 concentrations (rs=-0.04 for pollen and rs=0.23 for PM2.5).