Practical Diagnostic Accuracy of Nasopharyngeal Swab Testing for Novel Coronavirus Disease 2019 (COVID-19)

The novel coronavirus (SARS-CoV-2) is the cause of COVID-19, which has had a devastating international impact. Prior reports of testing have reported low sensitivities of nasopharyngeal polymerase chain reaction (PCR), and reports of viral co-infections have varied from 0-20%. Therefore, we sought to determine the accuracy of nasopharyngeal PCR for COVID-19 and rates of viral co-infection.

We conducted a retrospective chart review of all patients who received viral testing between March 1, 2020-April 28, 2020. Test results of a complete viral pathogen panel and COVID-19 testing were abstracted. We compared patients with more than one COVID-19 test for diagnostic accuracy against the gold standard of chart review.

We identified 1950 patients, of whom 1024 were tested for COVID-19. There were 221 repeat tests for COVID-19. Among patients with a repeat test, COVID-19 swabs had a sensitivity of 84.6% (95% confidence interval (CI), 69.5-94.4%) and a specificity of 99.5% (95%CI, 97-100%) compared to a clinical and radiographic criterion reference by chart review. We found viral co-infection rates of 2.3% in patients without COVID-19 and 6.1% in patients with COVID-19. Rates of co-infection appeared to be related to base rates of infection in the community and not a specific property of COVID-19.

COVID-19 nasopharyngeal PCR specimens are accurate but have imperfect sensitivity. Repeat testing for high-risk patients should be considered, and presence of an alternative virus should not be used to limit testing for COVID-19 for patients where it would affect treatment or isolation.