Role of Rapid Antigen Testing in Population-Based SARS-CoV-2 Screening

This study evaluates a population-based screening of asymptomatic people, using a rapid antigen diagnostic test (RADT), in areas of high transmission. To detect sources of SARS-CoV-2 infection, nasopharyngeal samples were taken and were tested using RADT. Confirmatory RT-qPCR tests were performed in both positive and negative cases. The internal validity of the RADT, the prevalence of infection, and the positive and negative predictive values (PPV and NPV) were estimated, based on the percentages of confirmed cases with 95% confidence interval. Of the 157,920 people registered, 50,492 participated in the screening; 50,052 were negative, and 440 were positive on the RADT (0.87%). A total of 221 positive RADT samples were reanalysed using RT-qPCR and 214 were confirmed as positive (96.8%; 95% CI: 93.5-98.7%), while 657 out of 660 negative RADT samples were confirmed as RT-qPCR negative (99.5%; 95% CI 98.7-99.9%). The sensitivity obtained was 65.1% (38.4-90.2%) and the specificity was 99.97% (99.94-99.99%). The prevalence of infection was 1.30% (0.95-2.13%). The PPVs were 95.4% (85.9-98.9%) and 97.9% (93.3-99.5%), respectively, while the NPVs were 99.7% (99.4-100%) and 99.2% (98.7-100%), respectively. The high specificity found allow us to report a high screening performance in asymptomatic patients, even in areas where the prevalence of infection was less than 2%.