Sensitivity of RT-PCR testing of upper respiratory tract samples for SARS-CoV-2 in hospitalised patients: a retrospective cohort study.

Williams, T. C.; Wastnedge, E.; McAllister, G.; Bhatia, R.; Cuschieri, K.; Kefala, K.; Hamilton, F. J.; Johannessen, I.; Laurenson, I. F.; Shepherd, J.; Stewart, A.; Waters, D.; Wise, H.; Templeton, K.

Objectives: To determine the sensitivity and specificity of RT-PCR testing of upper respiratory tract (URT) samples from hospitalised patients with COVID-19, compared to the gold standard of a clinical diagnosis. Methods: All URT RT-PCR testing for SARS-CoV-2 in NHS Lothian, Scotland, United Kingdom between the 7th of February and 19th April 2020 (inclusive) was reviewed, and hospitalised patients were identified. All URT RT-PCR tests were analysed for each patient to determine the sequence of negative and positive results. For those who were tested twice or more but never received a positive result, case records were reviewed, and a clinical diagnosis of COVID-19 allocated based on clinical features, discharge diagnosis, and radiology and haematology results. For those who had negative URT RT-PCR tests but a clinical diagnosis of COVID-19, respiratory samples were retested using a multiplex respiratory panel, a second SARS-CoV-2 RT-PCR assay, and a human RNase P control. Results: Compared to the gold standard of a clinical diagnosis of COVID-19, the sensitivity of an initial URT RT-PCR for COVID-19 was 82.2% (95% confidence interval 79.0-85.1%). Two consecutive URT RT-PCR tests increased sensitivity to 90.6% (CI 88.0-92.7%). A further 2.2% and 0.9% of patients who received a clinical diagnosis of COVID-19 were positive on a third and fourth test. Conclusions: The sensitivity of a single RT-PCR test of an URT sample in hospitalised patients is 82.2%. Sensitivity increases to 90.6% when patients are tested twice. A proportion of cases with clinically defined COVID-19 never test positive on URT RT-PCR despite repeated testing.