Combined throat/nasal swabs demonstrated a similar sensitivity to nasopharyngeal swabs alone in detecting SARS-CoV-2, according to research results published in European Journal of Clinical Microbiology & Infectious Diseases.
Study investigators found that this sensitivity was achieved despite a lower cycle threshold (Ct) value for the nasopharyngeal samples.
According to investigators, combined throat/nasal sampling has several advantages. They compared both methods by sampling on 107 healthcare workers with symptoms of coronavirus disease 2019 (COVID-19). The detection of virus was then performed by reverse transcription polymerase chain reaction (RT-PCR).
In total, 74.8% of sampled healthcare workers tested negative with both sampling methods and 23.4% tested positive with both methods. Discrepant results with positive PCR in combined throat/nasal swabs and negative PCR in nasopharyngeal swabs occurred twice. The κ index for concordance between both the methods was high (0.95) and the median Ct value of PCR on nasopharyngeal samples was significantly lower than that of PCR on combined throat/nasal samples at 19 vs 21 cycles (interquartile range 17-20 and 18-29, respectively; P =.01)
Investigators acknowledge that the study was limited by the low number of patients and positive samples. They did, however, determine that double sampling of additional workers was unnecessary because, “we did not observe any positive nasopharyngeal samples with negative throat/nasal swab.” They conclude that, despite the lower Ct value for nasopharyngeal samples, combined throat/nasal swabs yield a similar sensitivity to detect SARS-CoV-2. Investigators further suggest that “in future studies assessing the utility of different patient samples for the diagnosis of COVID-19, it would be interesting to compare the combined throat/nasal swab with saliva specimens as well.”
Vlek ALM, Wesselius TS, Achterberg R, Thijsen SFT. Combined throat/nasal swab sampling for SARS-CoV-2 is equivalent to nasopharyngeal sampling. [published online July 14, 2020]. Eur J Clin Microbiol Infect Dis. doi: 10.1007/s10096-020-03972-y