Combined throat/nasal swab sampling for SARS-CoV-2 is equivalent to nasopharyngeal sampling

Vlek, A. L. M.; Wesselius, T. S.; Achterberg, R.; Thijsen, S. F. T.

PURPOSE: PCR on a nasopharyngeal sample is the reference method for the detection of SARS-nCoV-2. However, combined throat/nasal sampling as a testing method has several advantages. We compared the combined throat/nasal sampling with nasopharyngeal sampling for detection of SARS-CoV-2 in healthcare workers suspected of COVID-19. METHODS: In 107 healthcare workers with symptoms of COVID-19, combined throat/nasal sampling and nasopharyngeal sampling was performed. Detection of SARS-CoV-2 was performed by RT-PCR targeting. RESULTS: A total of 80 healthcare workers (74.8%) tested negative with both sampling methods, and 25 healthcare workers (23.4%) tested positive with both sampling methods. There were two discrepant results with positive PCR in combined throat/nasal swabs and negative PCR in nasopharyngeal swabs (1.9%). The κ index for concordance between the 2 sampling methods was high (0.95). The median cycle threshold (Ct) value of PCR on nasopharyngeal samples was significantly lower than the Ct value of PCR on combined throat/nasal samples (19 (IQR 17–20) versus 21 (IQR 18–29) cycles, p value 0.01). CONCLUSION: Combined throat/nasal swabs yield a similar sensitivity to detect SARS-CoV-2 as nasopharyngeal swabs and are a good alternative sampling method, despite a lower Ct value for the nasopharyngeal samples.