In vitro diagnostics of coronavirus disease 2019: Technologies and application

On Pilot Massive COVID-19 Testing by Antigen Tests in Europe. Case Study: Slovakia

This paper provides a summary of mass COVID-19 testing of almost the entire population in Slovakia by antigen tests. We focused on the results delivered by two testing rounds and analyzed the benefits and weaknesses of such type of testing. We prepared mathematical models to critically examine the effectiveness of the testing, and we also estimated the number of potentially sick people that would become infected by those marked as positives by antigen tests. Our calculations have proven that antigen testing in hotspots can flatten the curve of daily newly reported cases significantly, but in regions with low-risk of COVID-19, the benefit of such testing is questionable. As for the regions with low infection rates, we could only estimate the proportion of true and false-positive cases because the national health authority had not validated the results by RT–PCR tests. Therefore, this work can serve as an introductory study on the first nationwide testing by antigen tests in Europe.

Comparison of Five Serological Assays for the Detection of SARS-CoV-2 Antibodies

Serological assays can contribute to the estimation of population proportions with previous immunologically relevant contact with the Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) virus. In this study, we compared five commercially available diagnostic assays for the diagnostic identification of SARS-CoV-2-specific antibodies. Depending on the assessed immunoglobulin subclass, recorded sensitivity ranged from 17.0% to 81.9% with best results for immunoglobulin G. Specificity with blood donor sera ranged from 90.2% to 100%, with sera from EBV patients it ranged from 84.3% to 100%. Agreement from fair to nearly perfect was recorded depending on the immunoglobulin class between the assays, the with best results being found for immunoglobulin G. Only for this immunoglobulin class was the association between later sample acquisition times (about three weeks after first positive PCR results) and positive serological results in COVID-19 patients confirmed. In conclusion, acceptable and comparable reliability for the assessed immunoglobulin G-specific assays could be shown, while there is still room for improvement regarding the reliability of the assays targeting the other immunoglobulin classes.

Testing for SARS-CoV-2

This review article describes the principles and implications of certain tests for diagnosing SARS-CoV-2 infections. The advantages and disadvantages of certain tests, both those in routine diagnostic application and those that have primarily research significance, are discussed. Also, a review of the practice of reporting results is given, as well as recommendations for its improvement.

Seroprevalence of SARS-CoV-2 infections among children visiting a hospital

IMPORTANCE

In this study, we retrospectively investigated the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies within serum samples from children in Beijing, China. These findings provide preliminary guidance regarding population susceptibility to SARS-CoV-2, which will aid in establishing policy toward coronavirus disease 2019 (COVID-19) prevention and control.

OBJECTIVE

To understand the seropositivity of anti-SARS-CoV-2 IgM/IgG antibodies among children in Beijing, China, evaluate the susceptibility of children in Beijing to SARS-CoV-2, and provide prima facie evidence to guide SARS-CoV-2 prevention and control.

METHODS

IgM/IgG antibody kits (colloidal gold) were used to conduct preliminary screening of SARS-CoV-2 IgM/IgG antibodies in serum samples of children who presented to Beijing Children's Hospital, Capital Medical University, having fever or requiring hospitalization, from March 2020 to August 2020. Statistical analysis of anti-SARS-CoV-2 antibody seropositivity was performed according to the children's general demographic characteristics, timing of admission to hospital, presence of pneumonia, and viral nucleic acid test results.

RESULTS

The study included 19 797 children with both IgM and IgG antibody results. Twenty-four children had anti-SARS-CoV-2 IgM-positive results (positive rate of 1.2‰), twelve children had anti-SARS-CoV-2 IgG-positive results (positive rate of 0.6‰). Viral nucleic acid test results were negative for the above-mentioned children with positive antibody findings; during the study, two children exhibited positive viral nucleic acid test results, but their anti-SARS-CoV-2 IgM/IgG antibody results were negative. Anti-SARS-CoV-2 IgM antibody seropositivity was higher in the <1-year-old group than in the ≥6-year-old group. The rates of anti-SARS-CoV-2 IgM seropositivity was highest in August from March to August; IgG results did not significantly differ over time. The rates of anti-SARS-CoV-2 IgM or IgG seropositivity among children with and without suspected pneumonia did not significantly differ between groups.

INTERPRETATION

During the study period, the rates of anti-SARS-CoV-2 IgM/IgG antibody seropositivity were low among children who presented to Beijing Children's Hospital, Capital Medical University. The findings suggest that children in Beijing are generally susceptible to SARS-CoV-2 infection; COVID-19 prevention and control measures should be strengthened to prevent disease in children.

Population-based seroprevalence surveys of anti-SARS-CoV-2 antibody: An up-to-date review

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has led to a global pandemic. However, the majority of currently available data are restricted to laboratory-confirmed cases for symptomatic patients, and the SARS-CoV-2 infection can manifest as an asymptomatic or mild disease. Therefore, the true extent of the burden of COVID-19 may be underestimated. Improved serological detection of specific antibodies against SARS-CoV-2 could help estimate the true numbers of infections. This article comprehensively reviews the associated literature and provides updated information regarding the seroprevalence of the anti-SARS-CoV-2 antibody. The seroprevalence can vary across different sites and the seroprevalence can increase with time during longitudinal follow-up. Although healthcare workers (HCWs), especially those caring for COVID-19 patients, are considered as a high-risk group, the seroprevalence in HCWs wearing adequate personal protective equipment is thought to be no higher than that in other groups. With regard to sex, no statistically significant difference has been found between male and female subjects. Some, but not all, studies have shown that children have a lower risk than other age groups. Finally, seroprevalence can vary according to different populations, such as pregnant women and hemodialysis patients; however, limited studies have examined these associations. Furthermore, the continued surveillance of seroprevalence is warranted to estimate and monitor the growing burden of COVID-19.

Evaluation of Humoral Immunity to SARS-CoV-2: Diagnostic Value of a New Multiplex Addressable Laser Bead Immunoassay

Despite efforts to develop anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody (Ab) immunoassays, reliable serological methods are still needed. We developed a multiplex addressable laser bead immunoassay (ALBIA) to detect and quantify anti-Spike S1 and nucleocapsid N Abs. Recombinant S1 and N proteins were bound to fluorescent beads (ALBIA-IgG-S1/N). Abs were revealed using class-specific anti-human Ig Abs. The performances of the test were analyzed on 575 serum samples including 192 from SARS-CoV-2 polymerase chain reaction-confirmed patients, 13 from seasonal coronaviruses, 70 from different inflammatory/autoimmune diseases, and 300 from healthy donors. Anti-S1 IgM were detected by monoplex ALBIA-IgM-S1. Comparison with chemiluminescent assays or enzyme-linked immunosorbent assays was performed using commercial tests. Multiplex ALBIA-IgG-S1/N was effective in detecting and quantifying anti-SARS-CoV-2 IgG Abs. Two weeks after first symptoms, sensitivity and specificity were 97.7 and 98.0% (anti-S1), and 100 and 98.7% (anti-N), respectively. Agreement with commercial tests was good to excellent, with a higher sensitivity of ALBIA. ALBIA-IgG-S1/N was positive in 53% of patients up to day 7, and in 75% between days 7 and 13. For ALBIA-IgM-S1, sensitivity and specificity were 74.4 and 98.7%, respectively. Patients in intensive care units had higher IgG Ab levels (Mann-Whitney test, p < 0.05). ALBIA provides a robust method for exploring humoral immunity to SARS-CoV-2. Serology should be performed after 2 weeks following first symptoms, when all COVID-19 (coronavirus disease 2019) patients had at least one anti-S1 or anti-N IgG Ab, illustrating the interest of a multiplex test.

Reliability of RT-PCR tests to detect SARS-CoV-2: risk analysis

The rapid escalation of the number of COVID-19 (Coronavirus Disease 2019) cases has forced countries around the world to implement systems for the widest possible testing of their populations. The World Health Organization (WHO) has in fact urged all countries to carry out as many tests as they can. Clinical laboratories have had to respond urgently to numerous and rising demands for diagnostic tests for SARS-CoV-2. The majority of laboratories have had to implement the RT-PCR (Reverse Transcriptase − Polymerase Chain Reaction) test method without the benefit of adequate experimental feedback. It is hoped that this article will make a useful contribution in the form of a methodology for the risk analysis of SARS-CoV-2 testing by RT-PCR and at the same time result reliability analysis of diagnostic tests, via an approach based on a combination of Fishbone Diagram and FMECA (Failure Mode, Effects, and Criticality Analysis) methods. The risk analysis is based on lessons learned from the actual experience of a real laboratory, which enabled the authors to pinpoint the principal risks that impact the reliability of RT-PCR test results. The probability of obtaining erroneous results (false positives or negatives) is implicit in the criticality assessment obtained via FMECA. In other words, the higher the criticality, the higher the risk of obtaining an erroneous result. These risks must therefore be controlled as a priority. The principal risks are studied for the following process stages: nucleic acid extraction, preparation of the mix and validation of results. For the extraction of nucleic acids, highly critical risks (exceeding the threshold set from experimentation) are the risk of error when depositing samples on the extraction plate and sample non-conformity. For the preparation of the mix the highest risks are a non-homogenous mix and, predominantly, errors when depositing samples on the amplification plate. For the validation of results, criticality can reach the maximum severity rating: here, the risks that require particular attention concern the interpretation of raw test data, poor IQC (Internal Quality Control) management and the manual entry of results and/or file numbers. Recommendations are therefore made with regard to human factor influences, internal contamination within the laboratory, management of reagents, other consumables and critical equipment, and the effect of sample quality. This article demonstrates the necessity to monitor, both internally and externally, the performance of the test process within a clinical laboratory in terms of quality and reliability.

Reliability of real-time RT-PCR tests to detect SARS-Cov-2: A literature review

In the face of the COVID-19 (Coronavirus Disease 2019) pandemic, the World Health Organization (WHO) has urged countries to test the population more widely. Clinical laboratories have been confronted with a huge demand for testing and have had to make urgent preparations for staff training, to establish new analytical processes, reorganize the workspace, and stock up on specific equipment and diagnostic test kits. The reliability of SARS-Cov-2 test results is of critical importance, given the impact it has on patient care and the management of the health crisis. A review of the literature available for the period leading up to and including June 2020 on the reliability of SARS-Cov-2 (Severe Acute Respiratory Syndrome Coronavirus) detection methods using real-time RT PCR (Reverse Transcription - Polymerase Chain Reaction) brings together the primary factors teams of scientists claim or demonstrate to affect the reliability of results. A description is given of the RT-PCR testing method, followed by a presentation of the characteristics and validation techniques used. A summary of data from the literature on the reliability of tests and commercial kits for SARS-Cov-2 detection, including current uncertainties with regard to the molecular targets selected and genetic diversity of SARS-Cov-2 is provided. The limitations and perspectives are then discussed in detail in the light of the bibliographic data available. Many questions have been asked that still remain unanswered. The lack of knowledge about this novel virus, which appeared at the end of 2019, has a significant impact on the technical capacity to develop reliable, rapid and practical tools for its detection.

A needle in the haystack? Assessing the significance of envelope (E) gene-negative, nucleocapsid (N2) gene-positive SARS-CoV-2 detection by the Cepheid Xpert Xpress SARS-COV-2 assay

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Controversy exists surrounding the clinical significance of high Crossing threshold (Ct) detections of SARS-CoV-2.

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Single target detection of SARS-CoV-2 (E-target-negative, N2-target positive) by the Cepheid Xpert Xpress SARS-Cov-2 accounted for 3.9 % of positive detections during a period of high COVID-19 activity (15.4 % overall positivity).

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Most patients with E-target-negative, N2-target-positive results were asymptomatic, but 25 % of those who underwent chest radiographic imaging had findings concerning for viral pneumonia suggesting subclinical infection.

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E-target-negative, N2-target-positive results were present in 8 symptomatic patients with a new diagnosis of COVID-19.

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Our findings suggest that the maximal PCR sensitivity is essential in hospital settings and that E-negative, N2-positive results can be significant.

The clinical significance of high crossing threshold (Ct) detection of SARS-CoV-2 by RT-PCR is inadequately defined. In the course of universal admission screening with the Cepheid Xpert Xpress SARS-CoV-2 assay at our institution, we observed that 3.9 % (44/1123) of SARS-CoV-2 positive results were negative for the envelope (E) gene target but positive for the nucleocapsid (N2) target. The overall SARS-CoV-2 positivity rate during the three-month study period was 15.4 % (1123/7285), spanning April-June 2020. The majority of patients with E-negative, N2-positive results were asymptomatic, with 29.5 % of patients symptomatic for COVID-19 at the time of presentation. Asymptomatic patients with E-negative, N2-positive results were significantly younger than symptomatic patients with the same results (average 37.6 vs. 58.4, p = 0.003). Similar proportions of prior SARS-CoV-2 positivity were noted among symptomatic and asymptomatic individuals (38.5 % vs. 33.3 %, p = 0.82). Among the 16 asymptomatic patients with radiographic imaging performed, four (25 %) had chest radiographic findings concerning for viral pneumonia. Interestingly, we observed an E-negative, N2-positive result in one patient with a previous SARS-CoV-2 by the Xpert Xpress that occurred 71 days prior. Critically, E-negative, N2-positive results were observed in 8 symptomatic patients with a new diagnosis of COVID-19. Thus, though concerns remain about extended SARS-CoV-2 RT-PCR positivity in some patients, the ability of clinical laboratories to detect patients with high Ct values (including E-negative, N2-positive results) is vital for retaining maximal sensitivity for diagnostic purposes. Our data show that a finding of E-positive, N2-negative SARS-CoV-2 should not be used to rule out the presence of subclinical infection.

Multicenter evaluation of two chemiluminescence and three lateral flow immunoassays for the diagnosis of COVID-19 and assessment of antibody dynamic responses to SARS-CoV-2 in Taiwan

This multicenter, retrospective study included 346 serum samples from 74 patients with coronavirus disease 2019 (COVID-19) and 194 serum samples from non-COVID-19 patients to evaluate the performance of five anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody tests, i.e. two chemiluminescence immunoassays (CLIAs): Roche Elecsys® Anti-SARS-CoV-2 Test (Roche Test) and Abbott SARS-CoV-2 IgG (Abbott Test), and three lateral flow immunoassays (LFIAs): Wondfo SARS-CoV-2 Antibody Test (Wondfo Test), ASK COVID-19 IgG/IgM Rapid Test (ASK Test), and Dynamiker 2019-nCoV IgG/IgM Rapid Test (Dynamiker Test). We found high diagnostic sensitivities (%, 95% confidence interval [CI]) for the Roche Test (97.4%, 93.4–99.0%), Abbott Test (94.0%, 89.1–96.8%), Wondfo Test (91.4%, 85.8–94.9%), ASK Test (97.4%, 93.4–99.0%), and Dynamiker Test (90.1%, 84.3–94.0%) after >21 days of symptom onset. Meanwhile, the diagnostic specificity was 99.0% (95% CI, 96.3–99.7%) for the Roche Test, 97.9% (95% CI, 94.8–99.2%) for the Abbott Test, and 100.0% (95% CI, 98.1–100.0%) for the three LFIAs. Cross-reactivity was observed in sera containing anti-cytomegalovirus (CMV) IgG/IgM antibodies and autoantibodies. No difference was observed in the time to seroconversion detection of the five serological tests. Specimens from patients with COVID-19 pneumonia demonstrated a shorter seroconversion time and higher chemiluminescent signal than those without pneumonia. Our data suggested that understanding the dynamic antibody response after COVID-19 infection and performance characteristics of different serological test are crucial for the appropriate interpretation of serological test result for the diagnosis and risk assessment of patient with COVID-19 infection.

Accuracy of a nucleocapsid protein antigen rapid test in the diagnosis of SARS-CoV-2 infection

Objectives

Rapid, reliable and easy-to-implement diagnostics that can be adapted in early severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) diagnosis are critical to combat the epidemic. SARS-CoV-2 nucleocapsid protein (NP) is an ideal target for viral antigen-based detection. A rapid and convenient method was developed based on fluorescence immunochromatographic (FIC) assay to detect the SARS-CoV-2 NP antigen. However, the accuracy of this diagnostic method needs to be examined.

Methods

This prospective study was carried out between 10 and 15 February 2020 in seven hospitals in Wuhan and one hospital in Chongqing, China. Participants with clinically suspected SARS-CoV-2 infection were enrolled. NP antigen testing by FIC assay and nucleic acid (NA) testing by real-time reverse transcriptase PCR (RT-PCR) were performed simultaneously in a blinded manner with the same nasopharyngeal swab sample. The diagnostic accuracy of NP antigen testing was calculated by taking NA testing of RT-PCR as the reference standard, in which samples with a cycle threshold (C_t) value of ≤40 were interpreted as positive for SARS-CoV-2.

Results

A total of 253 participants were enrolled; two participants were excluded from the analyses because of invalid NP testing results. Of 251 participants (99.2%) included in the diagnostic accuracy analysis, 201 (80.1%) had a C_t value of ≤40. With C_t value 40 as the cutoff of NA testing, the sensitivity, specificity and percentage agreement of the FIC assay was 75.6% (95% confidence interval, 69.0–81.3), 100% (95% confidence interval, 91.1–100) and 80.5% (95% confidence interval, 75.1–84.9) respectively.

Conclusions

With RT-PCR assay as the reference standard, NP antigen testing by FIC assay shows high specificity and relatively high sensitivity in SARS-CoV-2 diagnosis in the early phase of infection.

Assessing Viral Shedding and Infectivity of Asymptomatic or Mildly Symptomatic Patients with COVID-19 in a Later Phase

Background: The coronavirus disease (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a major global public health issue. SARS-CoV-2 infection is confirmed by the detection of viral RNA using reverse transcription polymerase chain reaction (RT-PCR). Prolonged viral shedding has been reported in patients with SARS-CoV-2 infection, but the presence of viral RNA does not always correlate with infectivity. Therefore, the present study aimed to confirm the presence of viable virus in asymptomatic or mildly symptomatic patients in the later phase of the disease, more than two weeks after diagnosis. Method: Asymptomatic or mildly symptomatic COVID-19 patients who had been diagnosed with the disease at least two weeks previously and admitted to a community treatment center (CTC) from 15 March to 10 April 2020 were enrolled in this study. Nasopharyngeal and salivary swab specimens were collected from each patient. Using these specimens, RT-PCR assay and viral culture were performed. Result: In total, 48 patients were enrolled in this study. There were no significant differences in baseline characteristics between the asymptomatic and mildly symptomatic patient groups. RT-PCR assay and viral culture of SARS-CoV-2 were performed using nasopharyngeal and salivary swabs. The results of RT-PCR performed using salivary swab specimens, in terms of cycle threshold (Ct) values, were similar to those of RT-PCR using nasopharyngeal swab specimens. In addition, no viable virus could be cultured from swab specimens collected from the late-phase COVID-19 patients with prolonged viral RNA shedding. Conclusions: In conclusion, our study suggests that even if viral shedding is sustained in asymptomatic or mildly symptomatic patients with later phase of COVID-19, it can be expected that the transmission risk of the virus is low. In addition, saliva can be used as a reliable specimen for the diagnosis of SARS-CoV-2 infection.

Enzyme-Linked Immunosorbent Assay for the Detection of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) IgM/IgA and IgG Antibodies Among Healthcare Workers

Background

The outbreak of the novel coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been spreading rapidly across the world. A nucleic acid real-time quantitative polymerase chain reaction (RQ-PCR) test of nasopharyngeal samples is the standard method for the diagnosis of an active SARS-CoV-2 infection. However, many limitations of the RQ-PCR tests make them unsuitable for the simple and rapid diagnosis of COVID-19 patients. Moreover, some individuals with COVID-19 present an asymptomatic infection. Thus, assessing the asymptomatic transmission of COVID-19, especially in healthcare workers (HCWs), is crucial for evaluating the efficiency of the current preventive measures. Serological tests such as enzyme-linked immunosorbent assay (ELISA) are needed to quickly identify a large number of asymptomatic carriers to prevent the further spread of the virus and assess level of possible serological immunity in a community.

Method

Between April 18 and June 17, 2020, 330 HCWs from five Madinah region-affiliated hospitals underwent a seroprevalence screening for anti-SARS-CoV-2 antibodies (immunoglobulin [Ig]M/IgA and IgG) using indirect ELISA testing.

Result

Among the 330 samples, 80 (24.24%) were positive for SARS-CoV-2 IgM/IgA and/or IgG antibodies. There were no significant differences observed in the seroprevalence among the different occupations of the HCWs (excluding the pharmacists) with respect to the percentage of their seropositive samples.

Conclusion

The current study presented the seroprevalence of anti-SARS-CoV-2 IgM/IgA and IgG antibodies in HCWs. The regular screening of HCWs for these antibodies is necessary; subsequently, a molecular test is recommended for those with seropositive (IgM, IgA, and IgG) samples to assess their viral load and potential shedding.

Six decades of lateral flow immunoassay: from determining metabolic markers to diagnosing COVID-19

Technologies based on lateral flow immunoassay (LFIA), known in some countries of the world as immunochromatographic tests, have been successfully used for the last six decades in diagnostics of many diseases and conditions as they allow rapid detection of molecular ligands in biosubstrates. The popularity of these diagnostic platforms is constantly increasing in healthcare facilities, particularly those facing limited budgets and time, as well as in household use for individual health monitoring. The advantages of these low-cost devices over modern laboratory-based analyzers come from their availability, opportunity of rapid detection, and ease of use. The attractiveness of these portable diagnostic tools is associated primarily with their high analytical sensitivity and specificity, as well as with the easy visual readout of results. These qualities explain the growing popularity of LFIA in developing countries, when applied at small hospitals, in emergency situations where screening and monitoring health condition is crucially important, and as well as for self-testing of patients. These tools have passed the test of time, and now LFIA test systems are fully consistent with the world's modern concept of ‘point-of-care testing’, finding a wide range of applications not only in human medicine, but also in ecology, veterinary medicine, and agriculture. The extensive opportunities provided by LFIA contribute to the continuous development and improvement of this technology and to the creation of new-generation formats. This review will highlight the modern principles of design of the most widely used formats of test-systems for clinical laboratory diagnostics, summarize the main advantages and disadvantages of the method, as well as the current achievements and prospects of the LFIA technology. The latest innovations are aimed at improving the analytical performance of LFIA platforms for the diagnosis of bacterial and viral infections, including COVID-19.

Comparison of automated SARS-CoV-2 antigen test for COVID-19 infection with quantitative RT-PCR using 313 nasopharyngeal swabs, including from seven serially followed patients

In routine clinical practice, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is determined by reverse-transcription PCR (RT-PCR). In the current pandemic, a more rapid and high-throughput method is in growing demand. Here, we validated the performance of a new antigen test (LUMIPULSE) based on chemiluminescence enzyme immunoassay. A total of 313 nasopharyngeal swabs (82 serial samples from 7 infected patients and 231 individual samples from 4 infected patients and 215 uninfected individuals) were analyzed for SARS-CoV-2 with quantitative RT-PCR (RT-qPCR) and then subjected to LUMIPULSE. We determined the cutoff value for antigen detection using receiver operating characteristic curve analysis and compared the performance of the antigen test with that of RT-qPCR. We also compared the viral loads and antigen levels in serial samples from seven infected patients. Using RT-qPCR as the reference, the antigen test exhibited 55.2% sensitivity and 99.6% specificity, with a 91.4% overall agreement rate (286/313). In specimens with > 100 viral copies and between 10 and 100 copies, the antigen test showed 100% and 85% concordance with RT-qPCR, respectively. This concordance declined with lower viral loads. In the serially followed patients, the antigen levels showed a steady decline, along with viral clearance. This gradual decline was in contrast with the abrupt positive-to-negative and negative-to-positive status changes observed with RT-qPCR, particularly in the late phase of infection. In summary, the LUMIPULSE antigen test can rapidly identify SARS-CoV-2-infected individuals with moderate to high viral loads and may be helpful for monitoring viral clearance in hospitalized patients.