Relation between the implementation of IPC measures and prevalence of anti-SARS-CoV-2 antibodies
SECONDARY
Based on the data collected during the first data collection period (December 2020/January 2021), we assessed whether the implementation of IPC measures was associated with the prevalence of anti-SARS-CoV-2 antibodies among pupils and staff in primary and secondary schools. Only schools that provided an answer for at least 10 out of 14 measures were included in this analysis. Furthermore, in order to have a scale based on uniformly registered and comparable information, measures that were not included in both primary and secondary schools were not included. We also excluded measures related to school or class closures, as the reverse causality of school closures and cases cannot be assessed in this study.Schools were classified according to their compliance with the implementation of IPC measure as ‘poor’, ‘moderate’ or ‘thorough’. This classification was based on the sum of Likert scale scores (each ranging from 1 to 5) for individual IPC measures. Schools in the upper quartile were designated as ‘thorough’, and schools in the lower quartile as ‘poor’ implementers. Schools with a sum of scores in between were considered ‘moderate’ implementers. If the Likert score was missing for a particular IPC measure in a school, we replaced the missing score by the mean score for that particular IPC measure from the other schools. If more than four measures were missing from the same school, it was not included in the analysis. For each of these three IPC measure compliance groups, the prevalence and 95% confidence interval (95% CI) of anti-SARS-CoV-2 antibodies among pupils and staff was calculated using generalized estimation equations to account for possible clustering of cases in schools. Generalized estimation equations for binomial outcomes with a log link function were used to assess if the implementation of IPC measures (poor, moderate, thorough) was associated with the prevalence of anti-SARS-CoV-2 antibodies, taking into account the community exposure (total reported cases in the school district 14 days before testing), socioeconomic tertile and language network (Dutch, French) of the school, type of school (primary, secondary), subject category (staff, pupil; when applicable), and school identification as the clustering variable with an exchangeable correlation structure. Results are expressed as an adjusted Relative Risk (aRR) with 95% CI. This analysis was done for all IPC measures together and for the IPC subcategories (ventilation, hygiene and physical distancing). We used data from the first collection period for this assessment, as this provided the most complete data (for example, during the second period less ventilation measures were assessed and for the third data collection period seroprevalence data were impacted by vaccination among staff).Data were analysed using SAS Enterprise Guide version 7.1 (SAS Institute Inc., Cary, NC, USA) and R version 4.0 (2021, R. Foundation for statistical computing, Vienna, Austria).