Potential usage of anterior nasal sampling in clinical practice with three rapid antigen tests for SARS-CoV-2

Introduction

Anterior nasal sampling (AN) might be more convenient for patients than NP sampling to diagnose coronavirus disease. This study investigated the feasibility of rapid antigen tests for AN sampling, and the factors affecting the test accuracy.

Methods

This single-center prospective study evaluated one qualitative (ESP) and two quantitative (LUMI and LUMI-P) rapid antigen tests using AN and NP swabs. Symptomatic patients aged 20 years or older, who were considered eligible for reverse-transcription quantitative polymerase chain reaction using NP samples within 9 days of onset were recruited. Sensitivity, specificity, and positive and negative concordance rates between AN and NP samples were assessed for the rapid antigen tests. We investigated the characteristics that affected the concordance between AN and NP sampling results.

Results

A total of 128 cases were recruited, including 28 positive samples and 96 negative samples. The sensitivity and specificity of AN samples using ESP were 0.81 and 1.00, while those of NP samples were 0.94 and 1.00. The sensitivity of AN and NP samples was 0.91 and 0.97, respectively, and specificity was 1.00, for both LUMI and LUMI-P. The positive concordance rates of AN to NP sampling were 0.87, 0.94, and 0.85 for ESP, LUMI, and LUMI-P, respectively. No factor had a significant effect on the concordance between the sampling methods.

Conclusions

ESP, LUMI, and LUMI-P showed practical diagnostic accuracy for AN sampling compared to NP sampling. There was no significant factor affecting the concordance between AN and NP sampling for these rapid antigen tests.

Performance of Qualitative and Quantitative Antigen Tests for SARS-CoV-2 Using Saliva

The rapid detection of SARS-CoV-2 is critical for the prevention of disease outbreaks. Antigen tests such as immunochromatographic assay (ICA) and chemiluminescent enzyme immunoassay (CLEIA) can yield results more quickly than PCR. We evaluated the performance of ICA and CLEIA using 34 frozen PCR-positive (17 saliva samples and 17 nasopharyngeal swabs [NPS]) and 309 PCR-negative samples. ICA detected SARS-CoV-2 in only 14 (41%) samples, with positivity rates of 24% in saliva and 59% in NPS. Notably, ICA detected SARS-CoV-2 in 5 of 6 samples collected within 4 days after symptom onset. CLEIA detected SARS-CoV-2 in 31 (91%) samples, with a positivity of 82% in saliva and 100% in NPS. These results suggest that the use of ICA should be limited to an earlier time after symptom onset and CLEIA is more sensitive and can be used in situations where quick results are required.

Immunochromatography and chemiluminescent enzyme immunoassay for COVID-19 diagnosis

Introduction

The rapid and accurate detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is required to prevent the spread of COVID-19. This study evaluated the utility of two SARS-CoV-2 antigen detection methods.

Methods

We evaluated two types of antigen detection methods using immunochromatography (Espline) and quantitative chemiluminescent enzyme immunoassay (Lumipulse). RT-PCR was performed as a standard procedure for COVID-19 diagnosis. Lumipulse and RT-PCR were performed for all 486 nasopharyngeal swabs and 136 saliva samples, and the Espline test was performed for 271 nasopharyngeal swabs and 93 saliva samples.

Results

The sensitivity and specificity of the Espline test were 10/11 and 260/260 (100%), respectively for the nasopharyngeal swabs and 3/9 and 84/84 (100%), respectively for the saliva samples. High sensitivities for both saliva (8/9) and nasopharyngeal swabs (22/24) were observed in the Lumipulse test. The specificities of the Lumipulse test for nasopharyngeal swabs and saliva samples were 460/462 (99.6%) and 123/127 (96.9%), respectively.

Conclusion

The Espline test is not effective for saliva samples but is useful for simple and rapid COVID-19 tests using nasopharyngeal swabs because it does not require special devices. The Lumipulse test is a powerful high-throughput tool for COVID-19 diagnosis because it has high detection performance for nasopharyngeal swabs and saliva samples.

The evaluation of three diagnostic tests for the detection of equine influenza nucleoprotein in nasal swabs

Background

Equine influenza (EI) is a highly contagious respiratory disease of horses.

Objectives

The aim of this study was to evaluate two rapid antigen detection kits (Directigen or DFA, and Espline) and a commercial ELISA for the detection of EI nucleoprotein in nasal swabs.

Method

Nasal swab samples from naturally and experimentally infected horses were used to compare the sensitivity and specificity of these assays to virus isolation (VI) and real-time RT-PCR.

Results

If real-time RT-PCR was considered as the gold standard, the sensitivity of the other tests in field samples was 68% (DFA), 35% (ELISA), 29% (Espline), and 9% (VI). These tests had 100% specificity when compared to real-time RT-PCR. A receiver operating characteristic (ROC) curve indicated that decreasing the cutoff of the ELISA would increase sensitivity with some loss of specificity. In samples from experimentally infected horses, the sensitivity of the tests compared with real-time RT-PCR was 69% (VI), 27% (DFA), 6% (Espline), and 2% (ELISA). The specificity was 100% for Espline and ELISA and 95% for VI and DFA.

Conclusions

This study illustrated that DFA is the most sensitive antigen detection test evaluated for the diagnosis of EI and that it can detect virus in some subclinical infected and vaccinated horses. The results suggest that DFA is a useful adjunct to laboratory tests and may be effective as a screening test in a quarantine station or similar facility where horses are monitored daily.