








key: cord-314829-tmgmqtjq
authors: Scohy, Anaïs; Anantharajah, Ahalieyah; Bodéus, Monique; Kabamba-Mukadi, Benoît; Verroken, Alexia; Rodriguez-Villalobos, Hector
title: Low performance of rapid antigen detection test as frontline testing for COVID-19 diagnosis
date: 2020-05-21
journal: J Clin Virol
DOI: 10.1016/j.jcv.2020.104455
sha: 
doc_id: 314829
cord_uid: tmgmqtjq

BACKGROUND: Ensuring accurate diagnosis is essential to limit the spread of the SARS-CoV-2 and for the clinical management of COVID-19. Although real-time reverse transcription polymerase chain reaction (RT- qPCR) is the current recommended laboratory method to diagnose SARS-CoV-2 acute infection, several factors such as requirement of special equipment and skilled staff limit the use of these time-consuming molecular techniques. Recently, several easy to perform rapid antigen detection tests were developed and recommended in some countries as the first line of diagnostic. OBJECTIVES: The aim of this study was to evaluate the performances of the Coris COVID-19 Ag Respi-Strip. Study design. We performed a comparison study by testing nasopharyngeal samples with RT-qPCR and antigen rapid test. RESULTS: 148 nasopharyngeal swabs were tested. Amongst the 106 positive RT-qPCR samples, 32 were detected by the rapid antigen test, given an overall sensitivity of 30.2%. All the samples detected positive with the antigen rapid tests were also positive with RT-qPCR. CONCLUSIONS: Highest viral load is associated with better antigen detection rates. Unfortunately, the overall poor sensitivity of the COVID-19 Ag Respi-Strip does not allow using it alone as the frontline testing for COVID-19 diagnosis.

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A week after alerting the WHO of a cluster of pneumonia of unknown etiology in Wuhan, the Chinese authorities announced on 7 January 2020 that a novel coronavirus was identified as the cause of these pneumonia. According to phylogenetic analysis, this novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), previously named 2019-nCoV, belongs to the B lineage of betacoronavirus genus and the sarbecovirus subgenus and has more than 85% J o u r n a l P r e -p r o o f nucleotide sequence identity with a bat SARS-like CoV genome published previously 1,2.

Initially described in China, the coronavirus disease (COVID-19) caused by SARS-CoV-2 rapidly gained ground and evidence of human-to-human transmission rose. On January 30, WHO declared COVID-19 outbreak a public health emergency of international concern and the disease has now spread worldwide. Highly sensitive and specific tests are crucial to identify and manage COVID-19 patients and implement control measures to limit the outbreak. Real 

The aim of this study was to assess the performances of COVID-19 Ag Respi-Strip as a frontline testing in comparison to molecular technique.

J o u r n a l P r e -p r o o f Nasopharyngeal swab specimens were collected from samples received at the microbiology department of the Cliniques universitaires Saint-Luc Hospital, a tertiary hospital of more than 900 beds in Brussels, between April 6 and April 21 2020. Samples were selected at random. If the rapid antigen test was not performed immediately, samples were stored at 4°C until the test. 

In a second time, some samples were ultracentrifuged at 31510g for 2 hours at 4°C. After discarding the supernatant, the 150 µL of residual sample were vortexed and analyzed by the rapid test. 

The criteria used for the performance assessment of COVID-19 Ag Respi-Strip were sensitivity and specificity. RT-qPCR was considered as the gold standard for this evaluation, therefore positive and negative samples by molecular techniques were considered to be true positive and true negative samples, respectively. The overall percentage of agreement and Cohen's kappa coefficient (κ) were used to evaluate assay agreement. Analyses were performed using GraphPad Prism 7.0 (GraphPad Prism Software Inc., San Diego, California) and MedCalc 19.2.0 (MedCalc Software Ltd, Ostend, Belgium).

We collected 148 nasopharyngeal samples from 148 patients. The median age of the study population was 57.5 (range: 0-94) with a sex ratio of 0.8 (64 men and 84 women). According 

In the ongoing pandemic context of COVID-19, diagnostic testing for SARS-CoV-2 is crucial in order to limit the spread of the virus as well as appropriately manage infected patients.

Different diagnostic test manufacturers have developed rapid tests based on SARS-CoV-2 proteins detection in respiratory samples. However, the analytical performances of these rapid antigenic tests depend on different factors including the viral load, the quality of the specimen and how it is processed. The performances also depend on the setting of patients tested.

Although the COVID-19 Ag Respi-Strip has several advantages such as the ease and fast achievement of the test, the rapid answer, the lower cost and the non-requirement of special equipment or skills compared with molecular techniques, data presented here suggested that this rapid test is suffering from poor sensitivity. The rapid antigen detection test is able to detect SARS-CoV-2 with high sensitivity in nasopharyngeal samples with high viral load equivalent at least to 1.7 x 10 5 copies/mL (Ct <25), but the sensitivity declines substantially when the viral load decreases with Ct values over 30, equivalent to 9.4 x 10 3 copies/mL, which is often the case in patients suffering of COVID-19. Actually, in our study, while the specificity was 100%, the overall sensitivity of the COVID-19 Ag Respi-Strip was 30.2%. This lack of sensitivity of rapid diagnostic tests for virus detection was already observed during the Influenza A (H1N1) pandemic 5. Ensuring accurate diagnosis is essential to limit the spread of the virus. The poor sensitivity of the COVID-19 Ag Respi-Strip leads to false negative results, which in these times of pandemic can be of great consequence. This rapid test was thought to be used as a first line COVID-19 diagnostic test in Belgium in order to possibility reduce the number of RT-qPCR testing in case of positive results, but requiring confirmation for negative results. However, because negative results cannot rule out SARS-CoV-2 infection, this test is of little use in a J o u r n a l P r e -p r o o f 

Log (copies/mL)

Genomic characterisation and epidemiology of 2019 novel coronavirus: implications for virus origins and receptor binding

A Novel Coronavirus from Patients with Pneumonia in China

Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR

Laboratory testing strategy recommendations for COVID-19. Interim guidance

Evaluation of rapid influenza diagnostic tests for detection of novel influenza A (H1N1) Virus -United States

COVID-19 Ag Respi-Strip tests were provided by Coris BioConcept, Gembloux, Belgium.

The authors declare no conflicts of interest. 

