key: cord-0991588-ghau55or
authors: Fernández-Villa, T; Vazquez-Casares, A; Rivero-Rodriguez, A; Carvajal-Ureña, A; Martín, V
title: Rapid antigen test for SARS-CoV-2 and primary health care
date: 2021-05-08
journal: J Infect
DOI: 10.1016/j.jinf.2021.05.001
sha: 618e31ca8ecce6b490dbec881acac79594d202f6
doc_id: 991588
cord_uid: ghau55or

nan

Fernández-Villa T 1 , Vazquez-Casares A 2 , Rivero-Rodriguez A 3 , Carvajal-Ureña A 4 , Martín V 1, 5 1 Research Group on Gene-Environment Interactions and Health (GIIGAS). Institute of Biomedicine (IBIOMED). Universidad 1 . This is, in our opinion, an excellent article about the usefulness of rapid antigen detection tests (RADTs) in the diagnosis of SARS-CoV-2 infection. Its strengths are that it is a real-life, primary care study, its careful design and the large and calculated sample size, congratulations. However, there are some issues that we believe should be highlighted and others that should be nuanced based on their results, especially with regard to policy implications. Firstly, we believe that the high specificity found in both, symptomatic and asymptomatic patients, close to 100%, has not been sufficiently highlighted. This near absence of false positives, as the authors comment, has been noted in other published articles. This finding is consistent with two recently published papers by our research group in two different contexts: population screening 2 and an outbreak in a nursing home 3 . As the authors conclude, this means that a positive test is a source of infection, but in both symptomatic and asymptomatic patients, so confirmatory tests are unnecessary. Based on the internal validity provided by the manufacturer, other authors recommend confirmatory testing in screening cases because of the expected high false positive rate 4 . It is well known that if the expected prevalence is higher than 1 -Specificity the positive predictive value will be very low and even all positives could be false positives 5 . However, if the prevalence is close to 100% the positive predictive value will be very high even with pre-test probabilities below 5%, which is the WHO recommended limit for the use of RADTs 6 . With regard to nuance, we were surprised that the authors praise the reliability of the negative results in symptomatic subjects and question those of asymptomatic subjects with similar results and with confidence intervals that overlap widely. In both cases we believe that a negative test does not rule out the presence of infection. Even in those cases where the reason for the request for testing is unknown, the pre-test probability is high, 7.8% 1 , and therefore a clear scenario of maintaining caution, the same in the case of close contacts, the quarantine situation should be maintained for the stipulated time regardless of the result of the test not only for antigen, but even for PCR 7, 8 . On the contrary, in a low pre-test probability scenario of less than 5%, as may be the case in population-based screening, the negative predictive value is very high and the presence of infection can be reasonably ruled out 2 . In any case, we would like to congratulate the COVID-19 Primary Care Research Group for its interesting work and just remind that diagnostic tests are not to be read but must be interpreted in their context.

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