key: cord-0841595-wik2vwfb
authors: Courtellemont, L.; Guinard, J.; Guillaume, C.; Giaché, S.; Rzepecki, V.; Seve, A.; Gubavu, C.; Baud, K.; Le Helloco, C.; Cassuto, G. N.; Pialoux, G.; Hocqueloux, L.; Prazuck, T.
title: High performance of a novel antigen detection test on nasopharyngeal specimens for diagnosing SARS‐CoV‐2 infection
date: 2021-03-01
journal: J Med Virol
DOI: 10.1002/jmv.26896
sha: bde4214107a1ec8f0869e7db066d8dd7cf8c7996
doc_id: 841595
cord_uid: wik2vwfb

The severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) pandemic has become a major public health issue worldwide. Developing and evaluating rapid and easy‐to‐perform diagnostic tests is a high priority. The current study was designed to assess the diagnostic performance of an antigen‐based rapid detection test (COVID‐VIRO(®)) in a real‐life setting. Two nasopharyngeal specimens of symptomatic or asymptomatic adult patients hospitalized in the Infectious Diseases Department or voluntarily accessing the COVID‐19 Screening Department of the Regional Hospital of Orléans, France, were concurrently collected. The diagnostic specificity and sensitivity of COVID VIRO® results were compared to those of real‐time reverse‐transcriptase quantitative polymerase chain reaction (RT‐qPCR) results. A subset of patients underwent an additional oropharyngeal and/or saliva swab for rapid testing. A total of 121 patients confirmed to be infected and 127 patients having no evidence of recent or ongoing infection were enrolled for a total of 248 nasopharyngeal swab specimens. Overall, the COVID‐VIRO® sensitivity was 96.7% (CI, 93.5%–99.9%). In asymptomatic patients, symptomatic patients having symptoms for more than 4 days and those with an RT‐qPCR cycle threshold value ≥ 32, the sensitivities were 100%, 95.8%, and 91.9%, respectively. The concordance between RT‐qPCR and COVID VIRO® rapid test results was 100% for the 127 patients with no SARS‐CoV‐2 infection. The COVID‐VIRO® test had 100% specificity and sensitivity greater than 95%, which are better than the recommendations set forth by the WHO (specificity ≥ 97%–100%, sensitivity ≥ 80%). These rapid tests may be particularly useful for large‐scale screening in emergency departments, low‐resource settings, and airports.

At the end of 2019, a pneumonia of initially unknown origin was first reported to the World Health Organization (WHO) Country Office in China. On January 9th, 2020, the Chinese health authorities and the WHO announced the discovery of a novel coronavirus, first named 2019-nCoV, then officially named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This virus, belonging to the coronavirus family but differing from SARS-CoV-1 and MERSCoV, is responsible for upper/lower respiratory tract infections known as coronavirus disease 2019 . The COVID-19 incubation period is approximately 5.2 days, and the most common onset symptoms are fever, cough, and fatigue. 1 Since SARS-CoV-2 emerged in China, it has become a major public health issue worldwide. To date, more than 40 million cases have been detected worldwide, 2 and the pandemic continues to spread unabated.

Minimizing testing delay seems to have the largest impact on reducing onward transmissions, 3 and the availability of highly sensitive and specific tests is essential to quickly identify new cases and contain virus transmission.

Currently, the real-time reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR) assay is the gold standard method to detect SARS-CoV-2 RNA in respiratory specimens such as nasopharyngeal or oropharyngeal swabs or bronchoalveolar lavage. 4 However, performing RT-qPCR is expensive, time-consuming, and requires special equipment and qualified operators. Faster, cheaper, and easier-to-use alternative tools could be represented by novel antigen-based rapid detection tests or point-of-care tests (POCTs). 5 Recently, the WHO approved the first rapid detection test for large-scale use in low-and middle-income countries, 6 and French health regulation authorities authorized their use in medical settings. 7 Several different POCTs have already been developed, 8 with generally high specificity but variable sensitivity. 9-21 COVID-VIRO® (AAZ) is one of the novel immunochromatographic tests designed to detect SARS-CoV-2 antigen in nasopharyngeal specimens with that of RT-qPCR as a reference test is the principal aim of the current study.

This study was approved by the Regional North West Ethics and Research Committee. Written informed consent was obtained from each participant.

People voluntarily accessing the COVID-19 Screening Department as well as subjects who tested SARS-CoV-2 positive in the previous 5 days and SARS-CoV-2 positive patients hospitalized in the Infectious Diseases Department of the Centre Hospitalier Régional (CHR) of Orléans, France, or Drouot Laboratory, Paris, France, from October 12th, 2020, to October 25th, 2020, were included in the study. The diagnosis of SARS-CoV-2 infection was confirmed in case of positivity of the specific RT-qPCR on nasopharyngeal swabs, in accordance with current recommendations. Subjects who recently tested positive for SARS-CoV-2 at the COVID-19 Screening Department were recontacted and retested within 5 days. The inclusion criteria were age ≥ 18 years old and agreement to undergo two concurrent nasopharyngeal swabs for RT-qPCR and COVID-VIRO® analysis. Patient age was collected at inclusion, as well as symptom onset date for symptomatic patients. Suggestive symptoms were headache, fatigue, fever, or upper or lower respiratory symptoms. Asymptomatic patients were defined as those not reporting any of these symptoms.

All SARS-CoV-2-positive subjects had confirmed RT-qPCR positivity within a maximum of 5 days before study sampling and were then retested in parallel with the rapid test.

SARS-CoV-2-negative subjects were patients having a negative RT-qPCR at the time of inclusion without any previous positive test.

Paired nasopharyngeal swabs were obtained for each patient by trained healthcare personnel (nurses, doctors, or biologists). The collection of the two simultaneous samples was always carried out by the same operator.

A polyester-tipped flexible (viral transport medium tube with swab VTM, Sun-Trine®) was inserted into two of the nostrils until resistance was felt at the nasopharynx, rotated six times, and withdrawn. After swabbing, the swab applicator was cut off. The first absorbent swab was placed into a vial containing 3 ml of inactivating viral transport media and was immediately transferred to the Virology Unit of the CHR of Orléans Hospital, Orléans, or Drouot Laboratory, Paris, to perform RT-qPCR. The rapid antigen test was immediately performed on-site with the second absorbent swab.

An additional oropharyngeal and/or saliva swab specimen was simultaneously collected in a subset of positive patients to determine the diagnostic reliability of these samples in comparison to nasopharyngeal swab specimens. Oropharyngeal specimens were collected on both sides of the tonsillar arches and posterior pharynx. 

Population characteristics are reported as percentages, mean and median values, standard deviations, and ranges. Data were analyzed in the Infectious Diseases Department.

To determine the diagnostic value of the COVID-VIRO®, the study population was stratified into two groups:

1. RT-qPCR-positive patients were already confirmed at the time of inclusion. A comparison between RT-qPCR and COVID-VIRO® results in these patients was used to assess diagnostic test sensitivity.

accessed the COVID-19 Screening Department to detect possible SARS-CoV-2 infection. To analyze the data, RT-qPCR-positive patients were added to the first group to assess diagnostic test sensitivity. Conversely, RT-qPCR-negative patients were selected to quantify the specificity of the rapid test.

The specificity and sensitivity of the COVID-VIRO® were calculated using the RT-qPCR results as reference tests, according to the following formulas:

The size of the study population was calculated on the basis of a 95% sensitivity with a lower margin of the confidence interval over 91% and a 99% specificity with a lower margin over 95% according to the WHO recommendations for antigenic rapid testing. The student's t-test was used to compare means. Table 1 ).

Among the 24 asymptomatic patients, no COVID-VIRO® falsenegative results were reported. Table 2 shows the COVID-VIRO® performances according to the C t value and the delay of symptom onset. COVID-VIRO® sensitivity was extremely high among patients having Gene N, S or ORF C t values ≥ 32, considering that 34 of 37 patients tested positive □ sensitivity: 91.9% (95% CI, 83.1%-100%). Table 3 reports the characteristics of the four COVID-VIRO® falsenegative cases. Three out of four had C t values ≥ 32 and were con- In the current study, the COVID-VIRO® sensitivity and specificity were 96.7% and 100%, respectively, with no observed false positives.

Although the results should be evaluated after 15 min, positive results almost always appeared within the first five minutes and often within one minute.

To date, several studies have evaluated the diagnostic performance of POCTs in real life, yielding conflicting data. [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] In general, the sensitivity ranged from 60.8% to 79.6%. [13] [14] [15] [16] [17] [18] Occasionally, significantly high sensitivity (93.9% and 98.3%) has been reported. [19] [20] [21] Concerning the Panbio COVID-19 Ag Rapid test (Abbott), the manufacturer reported high sensitivity (93.3%; 95% CI, 83.8-98.2) in a highly endemic setting in Brazil, 22 but other independent cohort studies have not confirmed these data. In 257 symptomatic and asymptomatic patients enrolled at the Emergency Department and Primary Health Care Setting in Spain, the overall sensitivity was 73.3%, reaching 86.5% among patients having symptoms for less than seven days. 11 In another multicentric study performed on 200 SARS-CoV-2-positive patients, the POCT sensitivity was 72.6% (95% CI, 64.5%-79.9%) in the Netherlands and 81.0% (95% CI, 69.0%-89.8%) in Aruba. The test sensitivity was as high as 95.2% (95% CI, 89.3%-98.5%) in patients with RT-qPCR test positivity for C t values < 32. 23 T A B L E 1 Performance of the COVID-VIRO® antigenic rapid test in the overall population and in the group of asymptomatic SARS-CoV-2infected patients Detection of viral RNA in nasopharyngeal samples is not necessarily related to infectiousness. 24 However, in the present study, the number of viral particles estimated by the C t value did not differ in asymptomatic and symptomatic SARS-CoV-2-infected patients. COVID-VIRO® appears to be as sensitive as RT-qPCR to detect infected patients in a limited number of asymptomatic patients.

Available data report that the RNA viral load rapidly decreases after the onset of symptoms, and infectiousness generally declines within 7-10 days. 24, [26] [27] [28] [29] 

The authors declare that there are no conflict of interests.

The data that support the findings of this study are available from the corresponding author upon reasonable request. 

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How to cite this article: Courtellemont L

High performance of a novel antigen detection test on nasopharyngeal specimens for diagnosing SARS-CoV-2 infection