key: cord-0792710-xqrj9rws
authors: Thell, R.; Kallab, V.; Weinhappel, W.; Mueckstein, W.; Heschl, L.; Heschl, M.; Korsatko, S.; Toedling, F.; Blaschke, A.; Herzog, T.; Klicpera, A.; Koeller, C.; Haugk, M.; Kreil, A.; Spiel, A.; Kreuzer, P.; Krause, R.; Sebesta, C.; Winkler, S.; Laky, B.; Szell, M.
title: Evaluation of a novel, rapid antigen detection test for the diagnosis of SARS-CoV-2
date: 2021-04-22
journal: nan
DOI: 10.1101/2021.04.22.21255637
sha: 8f57c033207bc27096ea0f1cbc86db263afbfbd8
doc_id: 792710
cord_uid: xqrj9rws

Background. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing coronavirus disease 2019 (COVID-19) is currently finally determined in laboratory settings by real-time reverse-transcription polymerase-chain-reaction (rt-PCR). However, simple testing with immediately available results are crucial to gain control over COVID-19. The aim was to evaluate such a point-of-care antigen rapid test (AG-rt) device in its performance compared to laboratory-based rt-PCR testing in COVID-19 suspected, symptomatic patients. Methods. For this prospective study, two specimen each of 541 symptomatic female (54.7%) and male (45.3%) patients aged between 18 and 95 years tested at five emergency departments (ED, n=296) and four primary healthcare centres (PHC, n=245), were compared, using AG-rt (positive/negative/invalid) and rt-PCR (positive/negative and cycle threshold, Ct) to diagnose SARS-CoV-2. Diagnostic accuracy, sensitivity, specificity, positive predictive values (PPV), negative predictive value (NPV), and likelihood ratios (LR+/-) of the AG-rt were assessed. Results. Differences between ED and PHC were detected regarding gender, age, symptoms, disease prevalence, and diagnostic performance. Overall, 174 (32.2%) were tested positive on AG-rt and 213 (39.4%) on rt-PCR. AG correctly classified 91.7% of all rt-PCR positive cases with a sensitivity of 80.3%, specificity of 99.1%, PPV of 98.3, NPV of 88.6%, LR(+) of 87.8, and LR(-) of 0.20. The highest sensitivities and specificities of AG-rt were detected in PHC (sensitivity: 84.4%, specificity: 100.0%), when using Ct of 30 as cut-off (sensitivity: 92.5%, specificity: 97.8%), and when the symptom onset was within the first three days (sensitivity: 82.9%, specificity: 99.6%). Conclusions. The highest sensitivity was detected with a high viral load. Our findings suggest that AG-rt are comparable to rt-PCR to diagnose SARS-CoV-2 in COVID-19 suspected symptomatic patients presenting both at emergency departments and primary health care centres.

INTRODUCTION diagnostics (IVD) assay, the SARS-CoV-2 Rapid Antigen Test (Roche Diagnostics), for the 108 detection of SARS-CoV-2 antigen. According to the manufacturer's manual [11] , the antigen test 109 shows 96.5% (95% CI 91.3% to 99.0%) of sensitivity and 99.7% (95% CI 98.2 to 99.9%) of 110 specificity. 111

Patients 114

Patients were recruited consecutively between October 30, 2020 and December 13, 2020 at five 115 emergency departments and four primary healthcare centres in Austria. The study was approved 116 by four provincial ethics commissions (EK20-249-1020, GS1-EK-3/182-2020, 33-064 ex 20/21, 117 ABT08GP-15681/2020-18). Signed informed consent was obtained from all participants. 118 591 symptomatic adults (≥18 years) were included, who were willing to undergo sampling twice. 119

Inclusion criteria were cough, fever, ageusia/anosmia, shortness of breath and sore throat. A total 120 of 49 (8.3%) patients were excluded for the following reasons: asymptomatic (n=12), children 121 (<18years, n=10), missing rt-PCR and/or AG-rt data (n=8), unknown symptoms (n=13), and 122 symptom onset more than two weeks prior to testing (n=6). 123 124 Procedure 125

Two swabs per patient were taken by experienced medical staff. The first probe was analysed 126 using the point-of-care device (SARS-CoV-2 Rapid Antigen Test (Roche Diagnostics). Outcome 127 was recorded 15 minutes after sampling as positive, negative, or invalid. Only one case 128

(1/542=0.2%), a 31 year old male patient with a sore throat two days prior testing and a negative 129 rt-PCR, showed an invalid AG-rt reading, which was not included in analysis. All rt-PCR 130 analyses using the second probe of each patient was conducted in hospital's laboratories or in 131 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted April 22, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 other special laboratories. Rt-PCR results were collected as quantitative (Ct) and qualitative 132 (positive or negative) parameters. Ct was reported in 202 of 213 cases. 133

Descriptive statistics was used to describe the characteristics of patients. The distribution of the 135 data was approximated by visual inspection of the histograms and the Kolmogorov Smirnov 136 tests. Normally distributed data were calculated as mean value with standard deviation (SD), 137 otherwise as median and range. 138

Continuous variables were compared between two groups with independent t-tests (parametric) 139 or Mann-Whitney U-tests (non-parametric). Chi-square or Fisher's exact tests were applied to 140 describe the relationship between proportions of categorical variables. Correlations between the 141 continuous parameters were performed using Spearman's rho. 142

Percentage accuracy in classification, sensitivity, specificity, positive predictive value (PPV), 143 and negative predictive value (NPV) were calculated. Positive (+) and negative (-) likelihood 144 ratios (LR) were calculated using sensitivity and specificity. The larger LR(+), the greater the 145 likelihood to be SARS-CoV-2 positive; and similarly, the smaller the LR(-), the lesser the 146 likelihood to be SARS-CoV-2 positive. All values are presented with their 95% confidence 147 interval (95% CI). 148

Statistical significance was set at a p-value of <0.05 (two-sided 

. CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The false negative tested patients (7.8%; ED: 30 and PHC: 12) included 50% females with an 180 average age of 53.0±17.2 years, the following symptoms: fever (n=29); cough (n=27); sore throat 181 (n=12); dyspnoea (n=12); and dysgeusia/anosmia (n= 5) with a median symptom onset of 3 182 (range, 0-14 days), and an average Ct of 31. 2±3.9 . 183 e at . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 22, 2021. ; https://doi.org/10.1101/2021.04.22.21255637 doi: medRxiv preprint (Supplement Table S1 ). 189 190 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 22, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 Diagnostic performance of the AG-rt at ED and PHC are presented in Table 2 . Interestingly, 191 sensitivity was lower and there were more than twice false negatives in ED compared to PHC. 192 193 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 22, 2021. ; https://doi.org/10. 1101 /2021 Sensitivities between ED and PHC regarding days of symptom onset are presented in Figure 2 . 201 202 203 Figure 2 Sensitivities (in % with 95% confidence interval in parenthesis) between ED and PHC 204 regarding days of symptom onset. 205 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 22, 2021. ; https://doi.org/10.1101/2021.04.22.21255637 doi: medRxiv preprint onset of symptoms between 8 and 14 days was associated with a far less sensitivity. However, 208 days of onset did not correlate with Ct (Spearman's rho=0.109; p=0.124). Details regarding 209 diagnostic performance of the AG-rt according symptom onset are presented in Table 3 . 210 211 CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 22, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 Sensitivities between ED and PHC regarding rt-PCR cut offs at 20, 25, 30, and 40 are presented 216 in Figure 3 . 217 218 219 Figure 3 Sensitivities (in % with 95% confidence interval in parenthesis) between ED and PHC 220 regarding rt-PCR cut offs. 221 222 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 22, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 and negative (Ct > 40), and at Ct values of 30, 25, and 20 are presented in Table 4 . The 224 highest sensitivity and specificity was detected when using Ct of 30 as cut-off. 225 226 Figure 4) . 235

. CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 22, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 22, 2021. ; https://doi.org/10.1101/2021.04.22.21255637 doi: medRxiv preprint not rapidly or timely available for every patient, the use of rt-PCR all too often is not adequate 244 neither in emergency departments nor in general practitioner's settings. Patient's flows are 245 crucial in the management of the disease, and so is the diagnostic flow in medical institutions 246 such as emergency departments or primary health care centres. 247

We found the SARS-CoV-2 Rapid Antigen Test (Roche Diagnostics) to produce an overall 248 sensitivity of 80.3% and specificity of 99.1% compared with rt-PCR, both in emergency 249 departments and primary health care centres. From symptom onset days 0 to 7, the sensitivity 250 was much better with 82.2%, whereas it reached 62.5% with disease onset from days 8 to 14. 251

Sensitivities were higher with lower PCR cycle threshold numbers. 252

Our results differ from the numbers claimed by the manufacturer, who reported a sensitivity of 253 96.5% and a specificity of 99.7%, who might have used specimens displaying higher viral 254

Sensitivities of antigen assays in previously published trials including a meta-analysis showed a 256 wide range from 45% to 86%.[9, 10, 12-14] Direct comparison exposes varieties in test systems, 257 onset of disease, performance of the procedure, presence of symptoms, testing institutions, and 258 others. Notably, in our trial results including sensitivities and specificities differed between ED 259 and PHC. We did not find a conclusive explanation for this fact; staffs and their respective 260 training did not differ in any of the centres substantially. 261

Only in few patients (0.6%) a false positive result was detected with the IVD compared to PCR 262 testing. The implication of this number however, is that those patients obviously apparently are 263 to be sequestered into quarantine jointly with patients with true positive results, as long as PCR 264 test results are pending. This requires a careful epidemiological reflection, when mass testing is 265 performed. 266 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted April 22, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 

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