False-positive results in SARS-CoV-2 antigen test with rhinovirus-A infection

Analysis of diagnostic performance and factors causing nonspecific reactions in SARS-CoV-2 rapid antigen detection tests

INTRODUCTION

Early diagnosis and appropriate infection control are important to prevent the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this study, we aimed to assess the diagnostic performance of SARS-CoV-2 rapid antigen detection (RAD) tests and the factors that cause nonspecific reactions.

METHODS

Nasopharyngeal swab specimens (n = 100), sputum specimens (n = 10), and lithium-heparin plasma samples (n = 100) were collected. We evaluated Espline®SARS-CoV-2 (Espline) and SARS-CoV-2 Rapid Antigen Test that also known as STANDARD Q® (STANDARD Q), with reverse transcription-polymerase chain reaction (RT-PCR) and Lumipulse® Presto SARS-CoV-2 Ag as reference tests. In addition, we investigated the effects of inadequate pretreatment methods and five potential causes of nonspecific reactions.

RESULTS

The sensitivities of Espline and STANDARD Q were 60% and 57%, respectively, and their specificity was 100%. It was confirmed that the judgment line for the positive insufficiently mixed specimens was faint. A false-positive result was observed with STANDARD Q when sputum was used as a specimen to investigate judgment the effect of viscosity.

CONCLUSIONS

Espline and STANDARD Q show good sensitivity for specimens with Ct values less than 25, but specimens collected within 9 days of symptom onset may still give false negatives. The test should be performed carefully, and the results should be judged comprehensively, taking into account clinical symptoms and patient background.

Laboratory Evaluation Links Some False-Positive COVID-19 Antigen Test Results Observed in a Field Study to a Specific Lot of Test Strips

During a household-transmission field study using COVID-19 antigen rapid diagnostic tests (Ag-RDT), a common test strip lot was identified among 3 participants with false-positive results. In blinded laboratory evaluation, this lot exhibited a significantly higher false-positive rate than other lots. Because a positive Ag-RDT result often prompts action, reducing lot-specific false positives can maintain confidence and actionability of true-positive Ag-RDT results.

Suspected Tuberculous Pleurisy and Coronavirus Disease 2019 Comorbidity

A 33-year-old woman with a fever, cough, and pharyngitis was admitted after left-sided pleural effusion was detected. The fever and upper respiratory symptoms were confirmed, and she was diagnosed with coronavirus disease (COVID-19) after showing a positive polymerase chain reaction (PCR) test. After thoracentesis, pleural fluid revealed elevated adenosine deaminase values and a positive QuantiFeron test; tuberculous pleurisy was thus suspected. Subsequent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) PCR and anti-SARS-CoV-2 Spike IgG tests were negative, suggesting that the initial PCR result had been erroneous. However, we were unable to confirm this. Data concerning COVID-19 diagnostics are insufficient at present. It is important to make comprehensive judgments regarding the diagnosis and treatment of patients as well as public health.

Potential for false-positive results with quantitative antigen tests for SARS-CoV-2: A case of a child with acute respiratory infection

The quantitative antigen test based on the chemiluminescent enzyme immunoassay for SARS-CoV-2 has been used in international airports for quarantine in Japan. While cases of false-positive rapid antigen tests for SARS-CoV-2 were reported, false-positive cases of the quantitative antigen test with clinical information are rare. Here, we report a case of acute respiratory infection whose quantitative antigen test for SARS-CoV-2 was suspected to be false positive. A 9-month-old boy who presented with fever and rhinorrhea was admitted to our hospital under the Quarantine Act. He was diagnosed with COVID-19 based on the quantitative antigen test for SARS-CoV-2 performed at the quarantine station. None of the accompanying family members were positive for COVID-19. Nucleic acid amplification tests (NAAT) for SARS-CoV-2 were all negative, and multiplex polymerase chain reaction detected human rhinovirus or enterovirus infection. This case suggests that the results of the quantitative antigen test should be interpreted together with clinical information, and NAAT should be performed when false-positive results are suspected to avoid unnecessary isolation.

Evaluation and clinical implications of the time to a positive results of antigen testing for SARS-CoV-2

INTRODUCTION

Antigen tests for severe acute respiratory coronavirus 2 sometimes show positive lines earlier than their specified read time, although the implication of getting the results at earlier time is not well understood.

METHODS

We prospectively collected additional nasopharyngeal samples from patients who had already tested positive for SARS-CoV-2 by reverse transcription PCR. The swab was used for an antigen test, QuickNavi™-COVID19 Ag, and the time periods to get positive results were measured.

RESULTS

In 84 of 96 (87.5%) analyzed cases, the results of QuickNavi™-COVID19 Ag were positive. The time to obtain positive results was 15.0 seconds in median (inter quartile range: 12.0-33.3, range 11-736) and was extended in samples with higher cycle thresholds (p < 0.001). Positive lines appeared within a minute in 85.7% of cases and within 5 min in 96.4%.

CONCLUSION

QuickNavi™-COVID19 Ag immediately showed positive results in most cases, and the time to a positive reaction may have indicated the viral load.

Diagnostic performance of a novel digital immunoassay (RapidTesta SARS-CoV-2): A prospective observational study with nasopharyngeal samples

Introduction

Digital immunoassays are generally regarded as superior tests for the detection of infectious disease pathogens, but there have been insufficient data concerning SARS-CoV-2 immunoassays.

Methods

We prospectively evaluated a novel digital immunoassay (RapidTesta SARS-CoV-2). Two nasopharyngeal samples were simultaneously collected for antigen tests and Real-time RT-PCR.

Results

During the study period, 1127 nasopharyngeal samples (symptomatic patients: 802, asymptomatic patients: 325) were evaluated. For digital immunoassay antigen tests, the sensitivity was 78.3% (95% CI: 67.3%–87.1%) and the specificity was 97.6% (95% CI: 96.5%–98.5%). When technicians visually analyzed the antigen test results, the sensitivity was 71.6% (95% CI: 59.9%–81.5%) and the specificity was 99.2% (95% CI: 98.5%–99.7%). Among symptomatic patients, the sensitivity was 89.4% (95% CI; 76.9%–96.5%) with digital immunoassay antigen tests, and 85.1% (95% CI; 71.7%–93.8%) with visually analyzed the antigen test, respectively.

Conclusions

The sensitivity of digital immunoassay antigen tests was superior to that of visually analyzed antigen tests, but the rate of false-positive results increased with the introduction of a digital immunoassay device.