Performance of SARS-CoV-2 antigen testing in symptomatic and asymptomatic adults: a single-center evaluation

Abstract

Background Antigen testing offers rapid and inexpensive testing for SARS-CoV-2 but concerns regarding performance, especially sensitivity, remain. Limited data exists for use of antigen testing in asymptomatic patients; thus, performance and reliability of antigen testing remains unclear. Methods 148 symptomatic and 144 asymptomatic adults were included. A nasal swab was collected for testing by Quidel Sofia SARS IFA (Sofia) as point of care. A nasopharyngeal swab was also collected and transported to the laboratory for testing by Cepheid Xpert Xpress SARS-CoV-2/Flu/RSV RT-PCR (Cepheid). Results Overall, Sofia had good agreement with Cepheid (> 95%) in adults, however was less sensitive. Sofia had a sensitivity of 87.8% and 33.3% for symptomatic and asymptomatic patients, respectively. Among symptomatic patients, testing > 5 days post symptom onset resulted in lower sensitivity (82%) when compared with testing within 5 days of symptom onset (90%). Of the four Sofia false-negative results in the asymptomatic cohort, 50% went on to develop COVID-19 disease within 5 days of testing. Specificity in both symptomatic and asymptomatic cohorts was 100%. Conclusions Sofia has acceptable performance in symptomatic adults when tested < 5 days of symptom onset. Caution should be taken when testing patients with ≥ 5 days of symptoms. The combination of low prevalence and reduced sensitivity results in relatively poor performance of in asymptomatic patients. NAAT-based diagnostic assays should be considered in when antigen testing is unreliable, particularly in symptomatic patients with > 5 days of symptom onset and asymptomatic patients.

Testing Frequency Matters | An Evaluation of the Diagnostic Performance of a SARS-CoV-2 Rapid Antigen Test in United States Correctional Facilities

“…[36] In alignment with prior studies, we found the sensitivity of rapid antigen testing to be significantly higher later in the course of infection (rapid antigen tests collected on the same day or after RT-PCR) and among residents exhibiting COVID-19 symptoms. [37,38] However, contrary to previous findings, we found the specificity to be significantly lower among symptomatic residents than among asymptomatic residents. [38][39][40] While, the magnitude of this difference was minimal for the one-rapid antigen test strategy (specificity among symptomatic residents was 5% lower than asymptomatic residents), the difference was larger (13%) for the three-rapid antigen test strategy.…”

The challenges of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing in low-middle income countries and possible cost-effective measures in resource-limited settings

“…It’s critical to confirm an antigen test result with a PCR test, especially if the result of the antigen rapid test contradicts the clinical setting. Therefore, PCR tests remain the gold standard, and their value remains high [ 73 , 75 ]. To be noted antigen rapid tests are typically used on symptomatic individuals since they perform best in symptomatic individuals and within a particular number of days of symptom onset [ 74 ].…”

Combined Diagnosis of SARS-CoV-2: Rapid Antigen Detection as an Adjunct to Nucleic Acid Detection

“…Frequent screening for SARS-CoV-2 in asymptomatic populations using antigen-based POCT has a very low detection rate and a high false-alarm rate. 24 Therefore, before using LFIA for COVID-19 screening, the characteristic distribution of the infected population, the accuracy of the LFIA kit, and the variation in sensitivity over time need to be carefully evaluated. When using LFIA for COVID-19 screening, it is necessary to increase the number of LFIA tests or combine LFIA with NAAT tests, especially in asymptomatic people and persons with symptomatic episodes >5 days.…”