The sampling efficiencies of commercial nasopharyngeal swabs

Upper respiratory tract samples are the most commonly used samples for coronavirus disease 2019 (COVID-19) diagnosis. The samples collected from the nasopharynx are preferred for viral nucleic acids detection. Commercial nasopharyngeal swabs (NPSs) are the major factor that influences the sampling quality. We here evaluated the acceptability and efficiency of NPSs from five manufacturers by examining the concentration of glyceraldehyde-3-phosphate dehydrogenase gene (GAPDH) retrieved from the swabs using the RT-PCR method. Significant different concentrations of GAPDH were detected, ranged from 4.36 × 10⁸ copies/mL to 6.98 × 10¹⁰ copies/mL among the five swabs (p < 0.05). The designation of the swab head, with or without tip expansion, had limited influence on the collection efficiency. The discrepancy among the NPSs emphasized the improvement of the swab head material.