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

Objective To 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). Methods NP 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. Results A 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 (κ) of 0.918 and 0.833 for Sure-Status and Biocredit, respectively. The overall 50% LoD and 95% LoD was 0.9-2.4 × 104 and 3.0-3.2 × 108 RNA copies/mL for NP swabs and 0.3-1.1 × 105 and 0.7-7.9 × 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. Conclusions the 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. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The work was funded by the Foundation of Innovative Diagnostics (FIND) ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethical approval was obtained from the National Research Ethics Service and the Health Research Authority (IRAS ID:28422, clinical trial ID: [NCT04408170][1]). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present work are contained in the manuscript [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT04408170&atom=%2Fmedrxiv%2Fearly%2F2023%2F04%2F04%2F2022.09.06.22279637.atom