key: cord-0863825-t4utndyv
authors: Ciotti, Marco; Maurici, Massimo; Pieri, Massimo; Andreoni, Massimo; Bernardini, Sergio
title: Performance of a rapid antigen test in the diagnosis of SARS‐CoV‐2 infection
date: 2021-02-09
journal: J Med Virol
DOI: 10.1002/jmv.26830
sha: 903463dd2a808798ed2e7f70494110dbb96f9c98
doc_id: 863825
cord_uid: t4utndyv

Diagnostics is crucial for a prompt identification of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infected patients, their isolation and treatment. Real‐time PCR is the reference method for the diagnosis of SARS‐CoV‐2 infection; however, the unprecedented increase in the number of infections worldwide calls for faster and easy methods that do not require skilled personnel and special equipment. Rapid antigen tests have been developed and used as first line screening. Here, we assessed the performance of a rapid antigen test in comparison to a real‐time qualitative PCR as gold standard. Fifty nasopharyngeal swabs from suspected cases of SARS‐CoV‐2 infection have been tested by Coris coronavirus disease 2019 Ag Respi‐Strip test and Allplex 2019n‐CoV assay. Of the 50 nasopharyngeal swabs tested, 11 were negative by both tests, 27 were negative by Ag test but positive by real‐time PCR, and 12 were positive by both methods. PCR detected the 39 positive samples at a median cycle threshold (Ct) value of 22.78 (mean: 24.51; range: 13.59–39.6). In the 12 concordant samples, the median Ct value was 17.37. The sensitivity of the Ag test was 30.77% (95% confidence interval [CI]: 17.02%–47.57%), specificity 100% (95% CI: 71.51%–100.00%), positive predictive value 100%, negative predictive value 85.25% (95% CI: 82.42%–87.69%), and accuracy 86.15% (95% CI: 73.45%–94.28%). The level of agreement between the two tests was poor, k = 0.164. The Ag test performs well in the presence of high viral loads, whereas lower levels are missed. Considering the poor sensitivity of the method, real‐time PCR remains the gold standard as front line screening for SARS‐CoV‐2 infection.

SARS-CoV-2 testing is needed to limit outbreak through identification of infected individuals and for contacts tracing. The ideal test would be no just the one capable of identifying the presence of SARS-CoV-2, but the one that is able to identify those individuals that can transmit the infection to others. They are probably those with the highest viral load in the upper respiratory tract, which usually occurs in the first days of infection. 3 Antigen tests have been indicated as the tests that have the potential of quickly identifying individuals that can transmit infectious viral particles. Although less sensitive than molecular tests that detect viral RNA, antigen tests perform well on individuals with high viral load in their upper respiratory tract. 4, 5 Antigen test is easy to perform, it does not requires skilled personnel and give results in about 15 min.

In this study, we compared the performance of a rapid antigen test, COVID-19 Ag Respi-Strip, with that of a real-time PCR assay, Allplex 2019n-CoV assay. 

We described the sample in terms of age (as mean, median and range in both assay), and sex ratio. The performance of Covid-19 Ag Respi-Strip was assessed calculating its sensitivity and specificity. Allplex 

A prompt diagnosis of suspected cases of SARS-CoV-2 infection is required for properly manage the infected patients as well as to limit the spread of the virus. Antigen tests respond to the need of rapidity, but their performance is conditioned by factors such as the viral load, the quality of the specimen and the processing phase. 

The authors declare that there are no conflict of interests.

Marco Ciotti conceived the study and wrote the manuscript;

Massimo Maurici performed the statistical analysis; Massimo Pieri performed the experiments; Massimo Andreoni and Sergio Bernardini, supervised the study and critically revised the manuscript.

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

https://orcid.org/0000-0002-9943-9130

Massimo Pieri https://orcid.org/0000-0002-3463-0268

A pneumonia outbreak associated with a new coronavirus of probable bat origin

A new coronavirus associated with human respiratory disease in China

Virological assessment of hospitalized patients with COVID-2019

The need for more and better testing for COVID-19

Low performance of rapid antigen detection test as frontline testing for COVID-19 diagnosis

Performance of a rapid antigen test in the diagnosis of SARS-CoV-2 infection