Molecular accuracy vs antigenic speed: SARS-CoV-2 testing strategies

Abstract

The pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has hit every corner of the world faster than any infectious disease ever known. In this context, rapid and accurate testing of positive cases are essential to follow the test-trace-isolate strategy (TETRIS), which has proven to be a key approach to constrain viral spread. Here, we discuss how to interpret and combine molecular or/and antigen-based detection methods for SARS-CoV-2 as well as when they should be used. Their application can be cleverly designed as an algorithm to prevent viral dissemination according to distinct epidemiological contexts within surveillance programs.

Keywords: Antigenic test; RT-PCR; SARS-CoV-2; Testing strategies.

Figure 1

SARS-CoV-2 infection time course and detection windows according to antigen and rtRT-PCR tests. The viral load and the diagnostic tests results represented in the scheme are based on nasopharyngeal swab samples. The time period indicated here refers to an unscaled range due to the infectious course diversity observed in SARS-CoV-2 positive cases. The onset of symptoms is stated at Day 0 and can result in different viral loads as represented.

Figure 2

Suggested algorithm for the implementation of SARS-CoV-2 antigen tests and requirements to couple with rtRT-PCR tests for an accurate diagnosis. Population Screening refers to the test performed to asymptomatic individuals with no known contact with a confirmed/suspected SARS-CoV-2 positive case, in order to attend recreational or social events, school screening, and international traveling in a vaccinated context. In this group, the antigen negative result may not need confirmatory testing due to low likelihood of SARS-CoV-2 infection. ∗ In the case of a negative antigen test result, quarantine should be performed until a new nasopharyngeal swab sample is obtained (5–7 days post the onset of symptoms or post confirmed/suspected exposure with a SARS-CoV-2 positive case) and processed by a rtRT-PCR assay.