key: cord-0856025-nsipl7d2
authors: Lindner, A. K.; Nikolai, O.; Rohardt, C.; Burock, S.; Hülso, C.; Bölke, A.; Gertler, M.; Krüger, L. J.; Gaeddert, M.; Tobian, F.; Lainati, F.; Seybold, J.; Jones, T. C.; Hofmann, J.; Sacks, J. A.; Mockenhaupt, F. P.; Denkinger, C.
title: Head-to-head comparison of SARS-CoV-2 antigen-detecting rapid test with professional-collected anterior nasal versus nasopharyngeal swab
date: 2020-12-07
journal: nan
DOI: 10.1101/2020.12.03.20243725
sha: 5d8cd4c1988188cba29ee378bbf73b6715143797
doc_id: 856025
cord_uid: nsipl7d2

Background: Nasopharyngeal (NP) swab samples for antigen-detecting rapid diagnostic tests (Ag-RDTs) require qualified healthcare professionals and are frequently perceived as uncomfortable by patients. Methods: We performed a manufacturer-independent, prospective diagnostic accuracy study, comparing professional-collected anterior nasal (AN) to nasopharyngeal swab, using the test kits of a WHO-listed SARS-CoV-2 Ag-RDT (STANDARD Q COVID-19 Ag Test, SD Biosensor), which is also being distributed by Roche. Individuals with high suspicion for COVID-19 infection were tested. The reference standard was RT-PCR using a combined oro-/nasopharyngeal swab sample. Percent positive and negative agreement, as well as sensitivity and specificity were calculated. Results: Among the 179 participants, 41 (22.9%) tested positive for SARS-CoV-2 by RT-PCR. The positive percent agreement of the two different sampling techniques for the Ag-RDT was 93.5% (CI 79.3-98.2). The negative percent agreement was 95.9% (CI 91.4-98.1). The Ag-RDT with AN-sampling showed a sensitivity of 80.5% (33/41 PCR positives detected; CI 66.0-89.8) and specificity of 98.6% (CI 94.9-99.6) compared to RT-PCR. The sensitivity with NP-sampling was 73.2% (30/41 PCR positives detected; CI 58.1-84.3) and specificity was 99.3% (CI 96.0-100). In patients with high viral load (>7.0 log10 RNA SARS-CoV2/swab), the sensitivity of the Ag-RDT with AN-sampling was 100% and 94.7% with NP-sampling. Conclusion: This study demonstrates that sensitivity of a WHO-listed SARS-CoV-2 Ag-RDT using a professional AN-sampling kit is at least equal to that of the NP-sampling kit, although confidence intervals overlap. Of note, differences in the IFUs of the test procedures could have contributed to different sensitivities. AN-sampling can be performed with less training, reduces patient discomfort, and it enables scaling of antigen testing strategies. Additional studies of patient self-sampling should be considered to further facilitate the scaling-up of Ag-RDT testing.

Antigen-detecting rapid diagnostic tests (Ag-RDTs) are likely to play a substantial role in innovative testing strategies for SARS-CoV-2 [1, 2] . Currently, most Ag-RDTs require nasopharyngeal (NP) swab samples. However, NP-sampling necessitates qualified healthcare professionals, thus limiting scale-up of testing.

We conducted a prospective diagnostic accuracy study with the objective to directly compare the performance of professional-collected anterior nasal (AN) versus NP swab, using a WHO-listed SARS-CoV-2 Ag-RDT. The reference standard was RT-PCR collected from a combined NP/oropharyngeal (OP) swab. The study was continued until 30 positive NP swab samples according to Ag-RDT were obtained, which is the minimum recommended by the WHO Emergency Use Listing Procedure to demonstrate sample type equivalency [3] . This manufacturer-independent study was conducted in partnership with the Foundation of Innovative New Diagnostics (FIND), the WHO collaborating centre for COVID-19 diagnostics.

Adults at high risk for SARS-CoV-2 infection according to clinical suspicion who attended the ambulatory SARS-CoV-2 testing facility of Charité University Hospital Berlin, Germany, were enrolled from 11-18 November 2020. Participants were excluded if either of the swabs for the Ag-RDT or the RT-PCR reference standard could not be collected.

Participants first underwent collection of the AN-sample, using the specific nasal swab provided in the test kit of the manufacturer, according to the instructions for use, which also correspond to the U.S. CDC instructions [4] . Briefly, while tilting the patient's head back 70 degrees, the swab was inserted about 2cm into each nostril, parallel to the palate until resistance was met at turbinates, then rotated 3-4 times against the nasal walls on each side. Subsequently, a separate NP-swab (provided in the manufacturer test kit) for the Ag-RDT and a combined OP/NP-swab (eSwab from Copan placed in 1ml

Amies medium) as per institutional recommendations for RT-PCR were taken from different sides of the nose.

The Ag-RDT evaluated was the STANDARD Q COVID-19 Ag Test (SD Biosensor, Inc. Gyeonggi-do, Korea; henceforth called STANDARD Q) [5] . Study procedures followed the same process as described in the prior study by Lindner et al [6] . The IFUs for AN-and NP-sampling showed differences, with a more elaborate extraction process and a higher volume of extracted specimen used for testing of ANsamples.

Of 181 patients invited, 180 (99.4%) consented to participate. One patient was excluded as both swabs for the Ag-RDT could not be obtained. The average age of participants was 36. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted December 7, 2020. ; of participants had one or more symptoms consistent with COVID-19. Duration of symptoms at the time of presentation on average was 4.2 days (SD 2.6). Among the 179 participants, 41 (22.9%) tested positive for SARS-CoV-2 by RT-PCR (Table 1) .

No invalid Ag-RDT results were observed on either AN-or NP-samples. Table 1) .

The strengths of the study are the standardized sampling methods, two independent blinded readers and an additional semi-quantitative assessment of Ag-RDT results. The cohort was representative, judging from the comparable sensitivity observed in the recent independent validation study of STANDARD Q (sensitivity 76.6%; CI 62.8-86.4) [7] . The study is limited as it was performed in a single centre.

In conclusion, this study demonstrates that sensitivity of a WHO-listed SARS-CoV-2 Ag-RDT using professional AN-sampling kit is at least equal to that of NP-sampling kit, although confidence intervals overlap. Of note, differences in the IFUs of the test procedures could have contributed to different sensitivities. AN-sampling can be performed with less training, reduces patient discomfort, and enables scaling of antigen testing strategies. Additional studies of patient self-sampling should be considered to further facilitate scale-up of Ag-RDT testing [6] . is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted December 7, 2020. ; https://doi.org/10.1101/2020.12.03.20243725 doi: medRxiv preprint TABLE 1 Antigen-detecting RDT results with a professional-collected AN swab and NP swab in RT-PCR positive patients from combined OP/NP swab. CT-values and viral load (in descending order) of the paired RT-PCR samples are shown, as well as the duration of symptoms per patient. The positive percent agreement between nasal AN and NP samples on Ag-RDT, and the respective sensitivities compared to RT-PCR are shown. . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted December 7, 2020. ; https://doi.org/10.1101/2020.12.03.20243725 doi: medRxiv preprint

European Centre for Disease Prevention and Control. Options for the use of rapid antigen tests for COVID-19 in the EU/EEA and the UK

European Centre for Disease Prevention and Control. Surveillance of COVID-19 at long-term care facilities in the EU/EEA

WHO. Instructions and requirements for Emergency Use Listing (EUL) submission: In vitro diagnostics detecting SARS-CoV-2 nucleic acid and rapid diagnostics tests detecting SARS-CoV-2 antigens

Interim Guidelines for Collecting, Handling, and Testing Clinical Specimens for COVID-19

COVID-19 Ag STANDARDTM Q COVID-19 Ag Test 2020

Head-to-head comparison of SARS-CoV-2 antigen-detecting rapid test with self-collected anterior nasal swab versus professional-collected nasopharyngeal swab

Evaluation of the accuracy, ease of use and limit of detection of novel, rapid, antigen-detecting point-ofcare diagnostics for SARS-CoV-2

The study was supported by FIND, Heidelberg University Hospital and Charité University Hospital internal funds, as well as a grant of the Ministry of Science, Research and the Arts of Baden-Württemberg, Germany. FIND provided input on the study design, and data analysis in collaboration with the rest of the study team.

Author contributions: AKL, LJK, FL and CMD designed the study and developed standard operating procedures. AKL and ON implemented the study design, enrolled patients, performed laboratory work and led the writing of the manuscript. FPM and JS coordinated and supervised the study site. CR, SB, CH, AB enrolled patients. MGe coordinated the testing facility. MGa and FT led the data analysis. TCJ and JH were responsible for PCR testing and contributed to the interpretation of the data. JAS supported the study design setup and the interpretation of the data. All authors have reviewed the manuscript.Data availability: All raw data and analysis code are available upon a request to the corresponding author.