Comparison of three nasopharyngeal swab types and the impact of physiochemical properties for optimal SARS-CoV-2 detection

Adequate swab specimen collection, release and detection of nucleic acids by molecular diagnostic assays is largely attributed to the physical and chemical characteristics of different swab types. We investigated properties of three types of commercial nasopharyngeal swabs (nylon flocked: Type 1-Media Merge; Type 2-Kang Jian Medical Apparatus, China and Type 3-Wuxi NEST Biotechnology Co. Ltd, China) used in clinical diagnostics with the aim to establish if different swab designs and configurations had any effect on swab performance. Properties investigated included viral absorption, release, capture, extraction and recovery efficiency from each swab for the detection of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). All swab types (n=18) were inoculated with different amounts of SARS-CoV-2 live viral cultures (1:10, 1:100 and 1:1000 copies/ml) and eluted in sterile phosphate buffer saline. RNA was extracted from all swab eluates using a fully automated system (BD MAX System) and cycle threshold (Ct) values were compared. RNA stability was also investigated after dry storage of swabs at room temperature for 72 hours. Statistically significant differences (p<0.05) were observed in the absorption and release capabilities between Type 1 and 3 as well as between Type 2 and 3 swabs, however, no significant difference was observed between Type 1 and 2. Ct values and extraction efficiency amounts of SARS-CoV-2 varied amongst the swab types. We conclude that in order to facilitate accurate SARS-CoV-2 diagnosis, assessment of NP swab characteristics is of importance before implementation for specimen collection in the clinical setting.