Impact of in-school antigen testing on the prevalence of asymptomatic SARS-CoV-2 carriers during the COVID-19 pandemic era

Abstract

In Austria, a nationwide antigen-test-based screening program for all students and educational staff in combination with intensified non-pharmaceutical mitigation measures were initiated in February 2021. We analyzed the first 6 weeks of this program and its impact on the prevalence of asymptomatic SARS-CoV-2 carriers. During the study period, we evaluated the results of 1 million students and approximately 150,000 educational staff members performing self-collected anterior-nasal swabs for antigen self-tests (ANAST) 1 to 3 times a week. Prevalence of asymptomatic SARS-CoV-2 carriers was monitored by an RT-qPCR based surveillance study in a representative school cohort. During the 6 weeks period, 6.979 persons tested positive by ANAST, corresponding to a weekly positivity rate of median 0.08% (range 0.04–0.13) and 0.22% (range 0.12–0.30) for students and educational staff, respectively. Compared to students, staff members had a significantly higher chance of testing positive in all analyzed weeks with odds ratios (OR) up to 3.4 (95% CI: 3.0–3.8). Per week a total of 78.5–89.7% (median 84.1%) of positive ANASTs were reported as isolated cases. Evaluating the prevalence of asymptomatic SARS-CoV-2 carriers with a model adjusted for regional community incidence, the OR for having an RT-qPCR-detected SARS-CoV-2 infection after initiation of the screening program compared to earlier periods was 0.31 (95% CI 0.17–0.54; p < 0.001). The screening program detected a considerable number of screening-positive individuals. Their prevalence was significantly lower during the screening program consistent with a potential contribution of in-school screening programs to reducing the spread of SARS-CoV-2 in educational settings.