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.

Viral load may impact the diagnostic performance of nasal swabs in nucleic acid amplification test and quantitative antigen test for SARS-CoV-2 detection.

INTRODUCTION: Compared to nasopharyngeal swabs (NPS), there has been insufficient evaluation of the diagnostic performance of nasal swabs (NS) for the detection of severe acute respiratory coronavirus 2 (SARS-CoV-2) in the nucleic acid amplification test (NAAT) and quantitative SARS-CoV-2 antigen test (QAT). METHODS: We prospectively compared healthcare worker-collected and flocked NS within nine days after symptom onset to paired NPS to detect SARS-CoV-2 in NAAT and QAT on the fully automated Lumipulse system. The agreement between sample types was evaluated, and cycle threshold (Ct) values and antigen levels were used as surrogate viral load measures. RESULTS: Sixty sets of NPS and NS samples were collected from 40 patients with COVID-19. The overall agreements between NAAT and QAT samples were 76.7% and 65.0%, respectively. In NAAT, the Ct value of NS was significantly higher, 5.9, than that of NPS. Thirty-nine (95.1%) NS tested positive in 41 positive-paired NPS with Ct ≤ 30. The negative correlation was observed between antigen levels of NS in QAT and Ct values of NS in NAAT (r = -0.88). In QAT, the antigen level of NS was significantly lower than that of NPS. Thirty-six (90.0%) NS tested positive in 40 positive-paired NPS with antigen levels >100 pg/mL, which were collected significantly earlier than those with antigen levels ≤100 pg/mL. CONCLUSIONS: In NAAT and QAT, NS had limited performance in detecting SARS-CoV-2 compared to NPS. However, NS may be helpful for patients with COVID-19 with high viral loads or those in the early stages of the illness.

Comparative study of rapid antigen testing and two nucleic acid amplification tests for influenza virus detection.

INTRODUCTION: This study aimed to evaluate rapid antigen detection (RAD) and rapid nucleic acid amplification tests (NAATs) to detect influenza virus (IV). METHODS: The conventional RAD test (Quick Chaser Flu A, B: QC), using silver amplified immunochromatography (Quick Chaser Auto Flu A, B: QCA), as well as two NAATs (Xpert Xpress Flu/RSV: Xpert, cobas Influenza A/B & RSV: cobas) were evaluated using nasopharyngeal swabs from suspected cases of influenza. A reference method was performed using real-time reverse transcription polymerase chain reaction according to the manual of the Japanese National Institute of Infectious Disease (NIID). RESULTS: From a total of 177 samples, 51 were positive according to the NIID assay. The kappa (κ) coefficient in Xpert and cobas for influenza A virus (IAV)/influenza B virus (IBV) was 1.00, which was the highest among the four detection assays. However, the κ coefficients in QC and QCA for IAV/IBV were 0.71-0.77 and 0.87-0.89, respectively. The sensitivities of the RAD tests were 41.7% in QC and 50.0% in QCA at < 6 h after onset, and 100.0% in both QC and QCA at 24-48 h after onset. The cycle threshold (Ct) values were significantly lower in the group in which all detection assays were positive for IAV. CONCLUSIONS: Xpert and cobas have comparable analytical performances and are highly useful as influenza virus detection assays. QC and QCA could show false negatives frequently in the early stage of infection and when viral load is low.

Does the timing of saliva collection affect the diagnosis of SARS-CoV-2 infection?

We evaluated the optimal timing of saliva sample collection to diagnose the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We obtained 150 saliva samples at four specific time points from 13 patients with confirmed SARS-CoV-2 infection. The time points were (1) early morning (immediately after waking), (2) immediately after breakfast before tooth brushing, (3) 2 h after breakfast, and (4) before lunch. On the 2nd hospital day, patients collected saliva at the four time points by themselves. We collected samples at two time points, (1) and (3), from the 3rd hospital day to day 9 following symptom onset. In 52 samples collected at the four time points, there was no significant difference. Meanwhile, there was no significant difference in the positive proportion or the viral load between the two time points in both analyses by the day from symptom onset and by all samples. In this study, there was no difference in the positive proportions in saliva collected at various time points within 9 days after symptom onset. The timing of saliva collection was not affected by the diagnosis of SARS-CoV-2 infection.

Evaluation of false positives in the SARS-CoV-2 quantitative antigen test.

INTRODUCTION: Highly sensitive reagents for detecting SARS-CoV-2 antigens have been developed for accurate and rapid diagnosis till date. In this study, we aim to clarify the frequency of false-positive reactions and reveal their details in SARS-CoV-2 quantitative antigen test using an automated laboratory device. METHODS: Nasopharyngeal swab samples (n = 4992) and saliva samples (n = 5430) were collected. We measured their SARS-CoV-2 antigen using Lumipulse® Presto SARS-CoV-2 Ag and performed a nucleic acid amplification test (NAAT) using the Ampdirect™ 2019 Novel Coronavirus Detection Kit as needed. The results obtained from each detection test were compared accordingly. RESULTS: There were 304 nasopharyngeal samples and 114 saliva samples were positive in the Lumipulse® Presto SARS-CoV-2 Ag test. All positive nasopharyngeal samples in the antigen test were also positive for NAAT. In contrast, only three (2.6%) of all the positive saliva samples in the antigen test were negative for NAAT. One showed no linearity with a dilute solution in the dilution test. Additionally, the quantitative antigen levels of all the three samples did not decrease after reaction with the anti-SARS-CoV-2 antibody. CONCLUSIONS: The judgment difference between the quantitative antigen test and NAAT seemed to be caused by non-specific reactions in the antigen test. Although the high positive and negative predictive value of this quantitative antigen test could be confirmed, we should consider the possibility of false-positives caused by non-specific reactions and understand the characteristics of antigen testing. We recommend that repeating centrifugation before measurement, especially in saliva samples, should be performed appropriately.

Evaluation of two commercial molecular diagnostic assays: The Xpert Norovirus and the TRCReady NV.

INTRODUCTION: Norovirus is highly contagious, and a few particles of this virus are sufficient to make people sick. It is desirable to develop quick and accurate laboratory methods to detect norovirus. METHODS: We evaluated two commercial molecular diagnostic assays, the Xpert Norovirus and the TRCReady NV, using clinical fecal samples. A reference method was performed using in-house real-time reverse transcriptase polymerase chain reaction (real-time RT-PCR). RESULTS: The results of the real-time RT-PCR analysis of 60 suspected cases of norovirus infection showed 5 cases of Genogroup I (GI) positives and 21 cases of GII positives, among which was 1 GI and GII coinfection. The viral titers of the norovirus-positive samples ranged from 1.54 × 101 to 3.14 × 108 copies/µL. Norovirus GII.17 (12 cases, 48%) was the most frequently detected genotype in this study, followed by GII.4 (6 cases, 24%), GII.13 (2 cases, 8%), GI.2 (2 cases, 8%), GI.3 (2 cases, 8%), GI.1 (1 case, 4%), and GII.2 (1 case, 4%). The kappa coefficient was 1.000 (95% CI: 1.000-1.000) for Xpert Norovirus and 0.966 (95% CI: 0.896-1.000) for TRCReady NV, indicating a strong agreement. CONCLUSIONS: Norovirus detection using Xpert Norovirus and TRCReady NV is highly useful for diagnosis and infection control because these assays are easy to operate, quick, and exhibit almost the same performance as that of real-time RT-PCR.

Clonality investigation of clinical Escherichia coli isolates by polymerase chain reaction-based open-reading frame typing method.

Escherichia coli (E. coli) causes urinary tract infections, pneumonia, surgical site infections, and bloodstream infections and is the important pathogen for both community-acquired and healthcare-associated infections. To investigate the clonality of E. coli is important for infection control and prevention. We aimed to investigate the clonality of clinical E. coli isolates using Cica Geneus E. coli polymerase chain reaction (PCR)-based open-reading frame typing (POT) KIT and clarify the clinical usefulness of this kit. About 124 E. coli isolates obtained from inpatients at Sapporo Medical University Hospital were used. The POT method was used to classify 124 clinical isolates into 87 POT numbers. In addition to the clonality, it was possible to obtain additional information that 20 of the 124 isolates were extended-spectrum ß-lactamase (ESBL) producing E. coli (5 isolates of CTX-M-1 group and 15 isolates of CTX-M-9 group) and 13 were sequence type (ST) 131 clone. Furthermore, when these ESBL-producing 20 isolates were compared with pulsed-field gel electrophoresis (PFGE) or multilocus sequence typing (MLST), Simpson's index of diversity was 0.968 in POT method, 0.979 in PFGE, and 0.584 in MLST. POT method had an analytical power similar to that of PFGE. In conclusion, attention should be paid to the difference in the interpretation of the results between the POT method and the PFGE, but POT method may be useful to timely monitor the spread of E. coli in medical facilities.

Inoculum effect of high concentrations of methicillin-susceptible Staphylococcus aureus on the efficacy of cefazolin and other beta-lactams.

The existence of a cefazolin inoculum effect (InE) of methicillin-susceptible Staphylococcus aureus (MSSA), which is speculated to be a reason for cefazolin treatment failure in MSSA infections, is controversial. In Japan, although cefazolin is one of the therapeutic choices for patients with MSSA infection, there are few reports of this effect. Additionally, the association between InE and blaZ type in beta-lactams other than cefazolin has not been well documented. In this study, we confirmed an MSSA InE in several beta-lactams, including cefazolin, and its relationship with blaZ, using 52 MSSA isolates from blood cultures. Three isolates (5.8%) that possessed type A blaZ showed a pronounced cefazolin InE. Five isolates (9.6%) showed pronounced InE with sulbactam/ampicillin; four isolates had type C blaZ and one had type A blaZ. However, we confirmed InE in MSSA isolates with blaZ not only type A and C but also B and D. For cefotaxime, ceftriaxone, imipenem, and meropenem, regardless of the presence of blaZ, we did not observe a significant increase in MICs at a high inoculum of MSSA. Hence, our results suggest that the above four beta-lactams are good alternatives to cefazolin if InE leads to treatment failure in a patient.