Reliability of a single-nostril nasopharyngeal swab for diagnosing SARS-CoV-2 infection

In this study we compared the viral load measured after collecting a single nasopharyngeal swab from each nostril to that obtained from the standard recommend double-nostril NOS. The study population consisted of 21 consecutive healthcare workers (median age 49 years, 67% females) undergoing routine molecular testing after been diagnosed with COVID-19 at the Pederzoli Hospital of Peschiera del Garda between December 2022 and January 2023. Three upper respiratory specimens were collected from each subject by the same skilled healthcare operator, as follows: 1 single-nostril right nasopharyngeal swab, 1 single-nostril left nasopharyngeal swab, followed by a double-nostril NOS. SARS-CoV-2 RNA was assayed with Xpert Xpress SARS-CoV-2 (Cepheid, Sunnyvale, CA, USA). No statistically significant differences were found between the median Ct values of the first (28.0; IQR; 23.3-31.5) and second (28.0; IQR; 23.3-32.6) single-nostril swabs taken from either nostril (p=0.472). No statistically significant differences were also observed in the median Ct values of NOS (28.9; IQR, 22.9-30.7) and that of the first single-nostril (p=0.236) or the second single-nostril (p=0.336) nasopharyngeal samples. No statistically significant difference could also be found in the median Ct values of single-nostril nasopharyngeal samples collected from the right (28.0; IQR, 23.0-31.7) and left (27.8; IQR, 23.5-31.9; p=0.325) nostrils. The results of our study confirm that collection of a nasopharyngeal swab from a single nostril may be a reliable and less invasive alternative for diagnosing SARS-CoV-2 infection than collecting the standard double-nostril NOS, thus contributing to reduce discomfort and potentially enhance testing compliance.