Abstract
We assessed the relationship between antigen and reverse transcription PCR (RT-PCR) test positivity and successful virus isolation. We found that antigen test results were more predictive of virus recovery than RT-PCR results. However, virus was isolated from some antigen-negative and RT-PCR‒positive paired specimens, providing support for the Centers for Disease Control and Prevention antigen testing algorithm.
Highlights
We assessed the relationship between antigen and reverse transcription PCR (RT-PCR) test positivity and successful virus isolation.We found that antigen test results were more predictive of virus recovery than RT-PCR results
Consistent with previous studies assessing the relationship between antigen tests, RT-PCR, and ability to culture virus [9–11], we found that SARS-CoV-2 was more likely to be recovered among specimen pairs for which antigen test and RT-PCR results were positive than among pairs in which antigen test results were negative and RT-PCR results were positive
Some studies have shown similar Positive predictive value (PPV) for viral culture when comparing RT-PCR and antigen tests [12], we found higher PPV for the antigen test than for RT-PCR [13], suggesting that antigen test positivity might be a better marker of infectiousness than a positive RT-PCR result
Summary
We placed the other specimen in viral transport medium and transported it on ice to the Marshfield Clinical Research Institute laboratory (Marshfield, Wisconsin, USA) for RT-PCR testing. All participants who had culture-positive specimens and false-negative antigen tests were symptomatic (7/9; 77.8%) or had a known exposure in the past 14 days (5/9; 55.6%). Among culture-positive symptomatic participants, those who had false-negative antigen and concordant positive antigen/RT-PCR results were tested a similar number of days after symptom onset (median 2 days vs 3 days) (Table 2). For those who had recoverable virus, nucleocapsid gene Ct values were significantly lower in those with concordant positive results (median 19.1, interquartile range 17.1–21.3) than those who had false-negative antigen test results (median 26.6, interquartile range 25.6–31.0) (p
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