Examination of the utility of the COVID-19 detection kit, TRC Ready® SARS-CoV-2 i for nasopharyngeal swabs.

The reverse transcription polymerase chain reaction (RT-PCR) offers high sensitivity, but has some drawbacks, such as the time required for the RNA extraction. Transcription reverse-transcription concerted reaction (TRC) Ready® SARS-CoV-2 i is easy to use and can be performed in about 40 minutes. TRC Ready® SARS-CoV-2 i and real-time one-step RT-PCR using the TaqMan probe tests of cryopreserved nasopharyngeal swab samples from patients diagnosed with COVID-19 were compared. The primary objective was to examine the positive and negative concordance rates. A total of 69 samples cryopreserved at -80° C were examined. Of the 37 frozen samples that were expected to be RT-PCR positive, 35 were positive by the RT-PCR method. TRC Ready® SARS-CoV-2 i detected 33 positive cases and 2 negative cases. One frozen sample that was expected to be RT-PCR positive was negative on both TRC Ready® SARS-CoV-2 i and RT-PCR. In addition, one frozen sample that was expected to be RT-PCR positive was positive by the RT-PCR method and negative by TRC Ready® SARS-CoV-2 i. Of the 32 frozen samples that were expected to be RT-PCR negative, both the RT-PCR method and TRC Ready® SARS-CoV-2 i yielded negative results for all 32 samples. Compared with RT-PCR, TRC Ready® SARS-CoV-2 i had a positive concordance rate of 94.3% and a negative concordance rate of 97.1%. TRC Ready® SARS-CoV-2 i can be utilized in a wide range of medical sites such as clinics and community hospitals due to its ease of operability, and is expected to be useful in infection control.

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 100 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.

Negative Results of Nucleic Acid Amplification Tests for SARS-CoV-2 in Clinical Practice May Vary among Six Molecular Assays in Patients with COVID-19.

Several commercial nucleic acid amplification tests (NAATs) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been developed. We used 6 kits available in Japan in 13 NAAT-positive specimens with crossing point values >36 and 7 NAAT-negative specimens from patients with coronavirus disease 2019 (COVID-19), and their results were compared. Specimens positive in ≥2 assays were considered true-positive and examined for concordance with the specimen results. The SARS-CoV-2 Detection Kit -Multi- (Toyobo M; Toyobo, Osaka, Japan) using extracted RNA had the highest concordance (κ = 1.00). This was followed by Cobas® SARS-CoV-2 (Roche, Basel, Switzerland) (κ = 0.79). There was a weak correlation between the number of negative results for each kit and the number of days between onset and testing (Spearman rank correlation: ρ = 0.44; P < 0.05). We believe that the variations in results among kits for specimens with low viral loads should not be problematic when these kits are used for screening infectious patients because these variations are more likely to be observed in specimens tested many days after onset (i.e., those that have lost their infectivity). However, it may be better to use a test for suspected late-stage COVID-19 with a low viral load, such as Toyobo M or Cobas.

Does the SARS-CoV-2 rapid antigen test result correlate with the viral culture result?

Rapid antigen tests (RATs) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have advantages over viral culture in terms of cost and rapidity of testing, but they have low sensitivity. In addition, RATs tend to be negative from approximately 11 days after symptom onset. To determine whether the antigen-negative state indicates a lack of infectiousness, we assessed the association between viral culture and RAT results. Viral culture, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and rapid antigen testing were performed on stored nasopharyngeal samples with threshold cycle values < 30, based on previous RT-qPCR testing. SARS-CoV-2 was isolated by viral culture from nine samples (45%) and one sample (17%) with positive and negative RAT results, respectively. The RAT and viral culture results were both associated with the viral load level and their cutoffs were similar, but the associations were not statistically significant. RAT might be a useful indicator of infectiousness, which can be helpful to control infection. However, further studies with larger sample size are warranted to confirm this observation.