Investigating the origin of the Belgian second SARS-CoV-2 wave by using (pre)admission screening samples

The goal of this study was to estimate rates of SARS-CoV-2 carriership and viral loads in the general Antwerp population and to compare the estimated prevalences and incidences with governmental data (numbers of detected positive cases, stringency measure index) in order to evaluate the dynamics leading to the second wave. We used (pre)admission screening results from the major Antwerp hospitals for estimating community prevalences and incidences. 43.545 samples were included (April – November 2020). High SARS-CoV-2 carriership rates (mean week prevalence of 1.3%) were found in the general Antwerp population. 35.4% of positive cases carried high viral loads. Only a small proportion (15.3%) of the viral circulation was detected by the nationally implemented testing policy. In the weeks before the second Belgian wave, increasing prevalences and incidences were found, together with country-wide easing of restriction measures. In our opinion these findings have led to origin of the second viral wave.