Head-to head comparison of anterior nares and nasopharyngeal swabs for SARS-CoV-2 antigen detection in a community drive-through test centre in the UK

ABSTRACT

ObjectiveTo conduct a head-to-head diagnostic accuracy evaluation of professionally taken anterior nares (AN) and nasopharyngeal (NP) swabs for SARS-CoV-2 antigen detection using rapid diagnostic tests (Ag-RDT). MethodsNP swabs for SARS-CoV-2 reverse transcription quantitative polymerase chain reaction (RT-qPCR) testing and paired AN and NP swabs for the antigen detection were collected from symptomatic participants enrolled at a community drive-through COVID-19 test centre in Liverpool. Two Ag-RDT brands were evaluated Sure-Status (PMC, India) and Biocredit (RapiGEN, South Korea). The visual read out of the Ag-RDT test band was quantitative scored and the 50% and 95% limit of detection (LoD) of both Ag-RDT brands using AN and NP swabs was calculated using a probabilistic logistic regression model. ResultsA total of 604 participants were recruited of which 241 (40.3%) were SARS-CoV-2 positive by RT-qPCR. Sensitivity and specificity of AN swabs was equivalent to the obtained with NP swabs 83.2% (75.2-89.4%) and 98.8% (96.5-99.6%) utilising NP swabs and 84.0% (76.2-90.1%) and 99.2% (97.0-99.8%) with AN swabs for Sure-Status and; 81.2% (73.1-87.7%) and 99.0% (94.7-86.5%) with NP swabs and 79.5% (71.3-86.3%) and 100% (96.5-100%) with AN swabs for Biocredit. The agreement of the AN and NP swabs was high for both brands with an inter-rater relatability ({kappa}) of 0.918 and 0.833 for Sure-Status and Biocredit, respectively. The overall 50% LoD and 95% LoD was 0.9-2.4 x 104 and 3.0-3.2 x 108 RNA copies/mL for NP swabs and 0.3-1.1 x 105 and 0.7-7.9 x 107 RNA copies/mL and for AN swabs with no significant difference on LoD for any of the swabs types or test brands. Quantitative read-out of test line intensity was more often higher when using NP swabs with significantly higher scores for both Ag-RDT brands. Conclusionsthe diagnostic accuracy of the two SARS-CoV-2 Ag-RDTs brands evaluated in this study was equivalent using AN swabs than NP swabs. However, test line intensity was lower when using AN swabs which could influence negatively the interpretation of the Ag-RDT results for lay users. Studies on Ag-RDT self-interpretation using AN and NP swabs are needed to ensure accurate test use in the wider community.