Journal of Infection and Chemotherapy

Asymptomatic patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection must be quickly identified and isolated to prevent the spread of the virus. The number of asymptomatic healthy people is completely unknown because they remain untested. Detection of specific SARS-CoV-2 antibodies has been widely accepted as a diagnostic test, and an immunochromatographic test, which is simpler and relatively cheaper than other methods, is becoming the gold standard for identifying healthy people who had been infected with SARS-CoV-2 in the past. In this study, 1,528 volunteers who worked at a particular hospital were subjected to an immunochromatographic IgG test for SARS-CoV-2 to determine the ratio of asymptomatic people. Only 12 volunteers (0.79%) were IgG+, with no significant background differences in the sex, age, profession, experiences of working at the emergency department or caring for coronavirus disease 2019 patients. If this IgG+ ratio was to be extrapolated to Wakayama citys population, 2,780 out of 3,54,063 people may be asymptomatic for SARS-CoV-2. The results imply that anyone may get infected with SARS-CoV-2 but remain asymptomatic.

Japan has reported a small number of COVID-19 cases relative to other countries. Because not all infected people receive diagnostic tests for COVID-19, the reported number of COVID-19 cases must be lower than the actual number of infections. Assessments of the presence of antibodies against the spike protein of SARS-CoV-2 can retrospectively determine the history of natural infection and vaccination. In this study, we assessed SARS-CoV-2 seroprevalence by analyzing over 60,000 samples collected in Japan from February 2020 to March 2022. The results showed that about 5% of the Japanese population had been infected with the virus by January 2021. The seroprevalence increased with the administration of vaccinations to adults; however, among the elderly, it was not as high as the vaccination rate, probably due to poor immune responses to the vaccines and waning immunity. The infection was spread during the epidemic waves caused by the SARS-CoV-2 Delta and Omicron variants among children who were not eligible for vaccination. Nevertheless, their seroprevalence was as low as 10% as of March 2022. Our study underscores the low incidence of SARS-CoV-2 infection in Japan and the effects of vaccination on immunity at the population level.

The situation of the COVID-19 pandemic in Japan is drastically changing in the 2nd year, 2021, due to the appearance of SARS-CoV-2 variants of concern and the roll-out of mass vaccination. In addition to PCR diagnosis, periodic seroepidemiologic surveillance is important to analyze the epidemic situation. In this study, we analyzed the rate of seropositivity for the SARS-CoV-2 N and S antigens in Hyogo prefecture, Japan in August 2021. Sera collected from people who received a health check-up in a clinic of the Hyogo Prefecture Health Promotion Association were subjected to analysis of reactivity to the SARS-CoV-2 N and S antigens by electrochemiluminescence immunoassay (ECLIA) and enzyme-linked immunosorbent assay (ELISA), respectively. For a total 1,000 sera, the positive rates to N and S antigens were 2.1% and 38.7%, respectively. The infectious rate estimated by serological analysis based on the presence of the anti-N antibody was 2.5-fold higher than the value reported based on PCR-based analysis, and it increased five-fold compared to the rate determined by our previous seroepidemiologic study in October, 2020. The anti-S positive rate was almost consistent with the vaccination rate in this area. The observed high anti-S antibody level in the seropositive population may indicate that the mass vaccination in Japan is being performed smoothly at this time point, although the infectious rate has also increased.

[Objective]Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody titers level and duration of elevated levels are considered important indicators for confirming the efficacy of coronavirus disease 2019 (COVID-19) vaccines. The objective of this study was to demonstrate the changes in antibody titers after the second and third doses of the COVID-19 vaccine, and to determine the antibody titers in cases of spontaneous infection with SARS-CoV-2 after vaccination. [Materials and Methods]From June 2021 to February 2023, IgG-type SARS-CoV-2 antibody titers were measured in 127 participants, including 74 outpatients and 53 staffs, at the Osaka Dental University Hospital (65 males and 62 females, mean age 52.3 {+/-} 19.1 years). [Results]Consistent with previous reports, the SARS-CoV-2 antibody titer decreased with time, not only after the second dose, but also after the third dose of the vaccine if there is no spontaneous COVID-19 infection. We also confirmed that the third booster vaccination was effective in increasing the antibody titer. 21 cases of natural infections were observed after administering two or more doses of the vaccine. 13 of these patients had post-infection antibody titers exceeding 40,000 AU/mL, and some cases continued to maintain antibody titers in the tens of thousands of AU/mL even after more than 6 months had passed since infection. [Conclusion]The rise in and duration of antibody titers against SARS-CoV-2 are considered important indicators for confirming the efficacy of novel COVID-19 vaccines. A longitudinal follow-up of antibody titers after vaccination in larger studies is warranted.

There are several recommendations for the use of personal protective equipment (PPE) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, the selection of appropriate PPE for the current situation remains controversial. We measured serum antibody titers for SARS-CoV-2 in 10 participants who were engaged in the operation of charter flights for the evacuation of Japanese residents from Hubei Province. All participants wore PPE in accordance with Centers for Disease Control and Prevention guidelines. A total of 17 samples were tested, and all were seronegative. Hence, we conclude that the current PPE recommendation is effective to protect healthcare workers from SARS-CoV-2 infection.

IntroductionAntigen testing is essential in the clinical management of COVID-19. However, most evaluations of antigen tests have been performed before the emergence of the Omicron variant. Thus, an assessment of the diagnostic performance of antigen tests for the detection of SARS-CoV-2 during the circulation of Omicron variant is required. MethodsThis prospective observational study evaluated QuickNavi-COVID19 Ag, a rapid antigen detection test between December 2021 and February 2022 in Japan, using real-time reverse transcription (RT)-PCR as a reference. Two nasopharyngeal samples were simultaneously collected for antigen testing and for RT-PCR. Variant analysis of the SARS-CoV-2 genomic sequencing was also performed. ResultsIn total, nasopharyngeal samples were collected from 1,073 participants (417 positive; 919 symptomatic; 154 asymptomatic) for analysis. Compared with those of RT-PCR, the sensitivity, specificity, positive predictive value, and negative predictive value were 94.2% (95% CI: 91.6%-96.3%), 99.5% (95% CI: 98.7%-99.9%), 99.2% (95% CI: 97.8%-99.8%), and 96.5% (95% CI: 94.8%-97.7%), respectively. The sensitivity among symptomatic individuals was 94.3% (95% CI: 91.5%-96.4%). Overall, 85.9% of sequences were classified as Omicron sublineage BA.1, 12.4% were Omicron sublineage BA.2, and 1.6% were Delta B.1.617.2. (Delta variant). Most of the samples (87.1%) had Ct values <25. ConclusionsThe QuickNavi-COVID19 Ag test showed high diagnostic performance for the detection of the SARS-CoV-2 Omicron sublineages BA.1 and BA.2 from nasopharyngeal samples.

IntroductionRapid qualitative antigen testing has been widely used for the laboratory diagnosis of COVID-19 with nasopharyngeal samples. Saliva samples have been used as alternative samples, but the analytical performance of those samples for qualitative antigen testing has not been sufficiently evaluated. MethodsA prospective observational study evaluated the analytical performance of three In Vitro Diagnostics (IVD) approved COVID-19 rapid antigen detection kits for saliva between June 2022 and July 2022 in Japan using real-time reverse transcription polymerase chain reaction (RT-PCR) as a reference. A nasopharyngeal sample and a saliva sample were simultaneously obtained, and RT-PCR was performed. ResultsIn total, saliva samples and nasopharyngeal samples were collected from 471 participants (140 RT-PCR-positive saliva samples and 143 RT-PCR-positive nasopharyngeal samples) for the analysis. The median Ct values were 25.5 (interquartile range [IQR]: 21.9-28.8) for saliva samples and 17.1 (IQR: 15.5-18.7) for nasopharyngeal samples (p<0.001). Compared with saliva samples of RT-PCR, the sensitivity and specificity were 46.4% and 99.7% for ImunoAce SARS-CoV-2 Saliva, 59.3% and 99.1% for Espline SARS-CoV-2 N, and 61.4% and 98.8% for QuickChaser Auto SARS-CoV-2, respectively. The sensitivity is >90% for saliva samples with a moderate-to-high viral load (Ct<25), whereas the sensitivity is <70% for high-viral-load nasopharyngeal samples (Ct<20). ConclusionCOVID-19 rapid antigen detection kits with saliva showed high specificities, but the sensitivities varied among kits, and the analytical performance of saliva qualitative antigen detection kits was much worse than that of kits using nasopharyngeal samples.

The rapid diagnosis of Campylobacter infections is important for the management of infectious gastroenteritis. Although stool culture is considered the gold standard, its sensitivity is limited and it requires prolonged incubation times. We performed a prospective multicenter study at nine healthcare facilities in Japan to evaluate a Campylobacter rapid antigen test using stool specimens between March 2024 and August 2025. Patients with suspected infectious gastroenteritis were consecutively enrolled and tested using QuickNavi-Campylobacter and compared with the FilmArray Gastrointestinal Panel as the reference method. Discordant results were further evaluated by culturing and additional PCR assays. In total, 410 patients were included in the final analysis. The positive, negative, and total concordance rates between QuickNavi-Campylobacter and FilmArray Gastrointestinal Panel were 79%, 99%, and 93%, respectively. The positive concordance rate decreased in specimens collected [&ge;] 6 days after the onset of symptoms (50%). QuickNavi-Campylobacter demonstrated relatively good concordance with the FilmArray Gastrointestinal Panel in a real-world multicenter setting. These results suggest that this rapid antigen test may be particularly useful for the early diagnosis of suspected campylobacteriosis.

BackgroundRapid antigen tests have been used to prevent the spread of the coronavirus disease 2019 (COVID-19); however, there have been concerns about their decreased sensitivity to the Omicron variant. AimsIn this study, we compared the sensitivity and specificity of the rapid antigen and the polymerase chain reaction (PCR) tests among the players and staff members of the Japan Professional Football League and clubs. Furthermore, we evaluated the relationship between the sensitivity and the duration from the onset of the symptoms to testing, the manufacturer of the rapid antigen test kits, and the PCR test analyte. Design and methodsThis was a retrospective observational study. We used 656 results from both the rapid antigen and PCR tests for COVID-19 using the analytes collected on the same day from January 12 to March 2, 2022, during the Omicron variant outbreak in Japan. ResultsThe sensitivity of the rapid antigen test compared with the PCR test was 0.63 (95% confidence interval: 0.54-0.72) and the specificity was 0.998 (95% confidence interval: 0.995-1.000). There were no significant associations between the sensitivity and the duration from the onset of the symptoms to testing (including asymptomatic cases in the category), vaccination status, manufacturer of the rapid antigen test kit or PCR analyte (P > 0.05) with small effect sizes (Cramers V or {varphi}: [&le;] 0.22). ConclusionsEven during the Omicron outbreak, the sensitivity of the rapid antigen tests did not depend on the duration from the onset of the symptoms to testing.

BackgroundRecent researches reported the impact of the coronavirus disease 2019 (COVID - 19) pandemic on the clinical practice of specific type cancers. The aim of this study was to reveal the impact of the COVID-19 outbreak on the clinical practice of various cancers. MethodsWe included hospitalized patients aged 18 years or older diagnosed between July 2018 and June 2020 with one of the top 12 most common cancers in Japan (colon/rectum, lung, gastric, breast, bladder & urinary tract, pancreas, non-Hodgkin lymphoma, liver, prostate, esophagus, uterus, and gallbladder & biliary tract) using Diagnostic Procedure Combination data, an administrative database in Japan. The intervention was defined April 2020 based on a declaration of emergency from Japanese government. The change volume of number of monthly admissions with each cancer was tested by interrupted time series (ITS) analysis, and monthly cases with radical surgery or chemotherapy for each cancer were descripted. Results403,344 cases were included during the study period. The most common cancer was colon/rectum (20.5%), followed by lung (17.5%). In almost cancer cases, the number of admissions decreased in May 2020. In particular, colorectal, lung, gastric, breast, uterine, or esophageal cancer cases decreased by over 10%. The number of admissions with surgery or chemotherapy decreased in colorectal, lung, gastric, breast, uterine, or esophageal cancer. ITS analysis indicated that cases with gastric or esophageal cancer were affected more than other type of cancer. ConclusionsThe COVID-19 outbreak has a negative impact on the number of admission cases with cancer; the magnitude of impact varied by cancer diagnosis.

AimsThe cycle threshold (Ct) value for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleic acid detection is important because of the criteria for quarantine management, including release from it, which are defined in Guidelines on the Novel Coronavirus-Infected Pneumonia Diagnosis and Treatment (Provisional 9th Edition, China). As this is also currently relevant because of the recent SARS-CoV-2 epidemic in Shanghai, we discuss the SARS-CoV-2 nucleic acid detection and its problems. We focus on the gene fragments and sample types involved in nucleic acid detection and their effect on the latest criteria for release from quarantine. MethodsA total of 215 patients with SARS-CoV-2 infection were included. Pharyngeal swabs (nasopharyngeal swabs plus oropharyngeal swabs) were collected in the early stage of the disease, and pharyngeal swabs, sputum samples, and anal swabs were collected both in the middle and advanced stages of the disease. The Open reading frame 1ab (ORF lab) gene, Nucleocapsid (N) gene and Envelop (E) gene of each sample were quantitatively analyzed using fluorescence qPCR technique. ResultsExclusion of the E gene detection results had no significant effect on the interpretation of the nucleic acid Ct value of 35, with a positive concordance rate of 98.7% (95% CI 86.0%-100%) and an overall concordance rate of 99.7% (95% CI 92.9%-100%). The kappa coefficient was 0.99 (95% CI 0.92-1.00). Compared with nucleic acid detection using both pharyngeal swab and sputum sample, the positive concordance rate of the detection using pharyngeal swab alone was 47.6% (95% CI 27.8%-99.3%). The kappa coefficient was 0.63 (95% CI 0.53-0.75), and the consistency was not ideal. ConclusionsNucleic acid detection using the ORF 1ab gene and the N gene can achieve the purpose of SARS-CoV-2 detection. Nucleic acid detection using sputum samples is significant in the determination of Ct values and its significance in the development of the criteria for release from quarantine needs to be taken into account. It is suggested that to increase the accuracy of nucleic acid detection, instead of unilaterally pursuing increasing the number of target genes for amplification and improving PCR techniques, more attention should be paid to sampling and sample reliability, as well as strict quality control of the detection process.

Serological evaluation with SARS-CoV-2 specific IgG antibody will be an alternative way to know the pandemic of novel coronavirus disease (COVID-19) if the capacity for diagnostic PCR test is limited. The point-of-care test to detect SARS-CoV-2 specific IgG antibody in peripheral blood (n =202) was performed in two community clinics in Tokyo, Japan. The overall positive rate of SRAS-CoV-2 IgG antibody was 5.9% (95% confidence interval[CI]: 3.1-10.1). Higher rate was observed for healthcare workers (n =55, 9.1 [3.0-20.0]). The limitation on antibody tests includes low sensitivity and potent cross-reactivity with the previous coronavirus. Robust healthcare policy to efficiently monitor COVID-19 spread is warranted in Tokyo.

As SARS-CoV-2 and its variants continue to spread, a reliable and convenient alternative to nasopharyngeal swabbing and RT-PCR testing is needed. To test the usability and performance of saliva sample collection, saliva, nasal and nasopharyngeal swab specimens were collected from a total of 338 individuals consisting of confirmed COVID-19 patients and healthy subjects. To evaluate the diagnostic accuracy of self-collected and performed SARS-CoV-2 rapid antigen test on saliva and nasal swabs specimens, we compared its performance to nasopharyngeal swab specimen RT-PCR as a comparator test. In saliva specimens, the positive percent agreement was 90.14%, and the negative percent agreement was 99.61%, while in nasal swab specimens, the positive percent agreement was 91.55%, and the negative percent agreement was 100%, both meeting the sensitivity and specificity criteria required by the FDA. Therefore, when considering both the reliability and convenience of testing, we found saliva testing to be the better method for large-scale and frequent self-testing.

ImportanceFatality rates related to COVID-19 in Japan have been low compared to Western Countries and have decreased despite the absence of lockdown. Serological tests monitored across the course of the second wave can provide insights into the population-level prevalence and dynamic patterns of COVID-19 infection. ObjectiveTo assess changes in COVID-19 seroprevalence among asymptomatic employees working in Tokyo during the second wave. DesignWe conducted an observational cohort study. Healthy volunteers working for a Japanese company in Tokyo were enrolled from disparate locations to determine seropositivity against COVID19 from May 26 to August 25, 2020. COVID-19 IgM and IgG antibodies were determined by a rapid COVID19 IgM/IgG test kit using fingertip blood. Across the company, tests were performed and acquired weekly. For each participant, serology tests were offered twice, separated by approximately a month, to provide self-reference of test results and to assess for seroconversion and seroreversion. SettingWorkplace setting within a large company. ParticipantsHealthy volunteers from 1877 employees of a large Japanese company were recruited to the study from 11 disparate locations across Tokyo. Participants having fever, cough, or shortness of breath at the time of testing were excluded. Main Outcome(s) and Measure(s)Seropositivity rate (SPR) was calculated by pooled data from each two-weeks window across the cohort. Either IgM or IgG positivity was defined as seropositive. Changes in immunological status against SARS-CoV-2 were determined by comparing results between two tests obtained from the same individual. ResultsSix hundred fifteen healthy volunteers (mean + SD 40.8 + 10.0; range 19 - 69; 45.7 % female) received at least one test. Seroprevalence increased from 5.8 % to 46.8 % over the course of the summer. The most dramatic increase in SPR occurred in late June and early July, paralleling the rise in daily confirmed cases within Tokyo, which peaked on August 4. Out of the 350 individuals (mean + SD 42.5 + 10.0; range 19 - 69; 46.0 % female) who completed both offered tests, 21.4 % of those individuals who tested seronegative became seropositive and seroreversion was found in 12.2 % of initially seropositive participants. 81.1% of IgM positive cases at first testing became IgM negative in approximately one month. Conclusions and RelevanceCOVID-19 infection may have spread widely across the general population of Tokyo despite the very low fatality rate. Given the temporal correlation between the rise in seropositivity and the decrease in reported COVID-19 cases that occurred without a shut-down, herd immunity may be implicated. Sequential testing for serological response against COVID-19 is useful for understanding the dynamics of COVID-19 infection at the population-level.

IntroductionVaccination programs are important to preventing COVID-19 infection. BNT162b2 is new type of vaccine, and previous studies have shown that the antibody response was significantly elevated in patients with prior COVID-19 infection after the first vaccination. However, no study has evaluated the efficacy of the vaccination or the adverse reactions of people with prior COVID-19 infection in Japan. The aim of this study is to evaluate the antibody titer and adverse reactions of BNT162b2 vaccine among participants with prior COVID-19 infection in Japan. MethodsThe data for this study was collected between April 15, 2021, and June 9, 2021. All of the hospital staff who received the BNT162b2 vaccine were included in this study and were sorted into either the prior infection group or the control group. We collected the data of adverse reactions through self-reporting and calculated the anti-SARS-CoV-2 spike-specific antibody titer for all participants. ResultsThe antibody titer of the prior-infection group in first antibody test was significantly higher than that of the control group in the second antibody test. There was no significant difference in adverse reactions between the prior infection group receiving its first vaccination and the control group receiving its second vaccination. ConclusionOur study shows that the antibody response following the first vaccination in the prior COVID-19 infection group was found to be comparable to that of the second vaccination in the control group; however, the evaluation of adverse reactions was inadequate and further, large-scale studies are needed.

BackgroundThe Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), designated as a variant of concern by the World Health Organization, spreads globally and was confirmed as the cause of the Omicron wave of the coronavirus disease 2019 (COVID-19) pandemic in Shanghai, China. The viral shedding duration of Omicron variants needs to be determined. MethodsWe retrospectively analyzed 382 patients admitted to a shelter hospital for COVID-19. Of the patients, 8 patients were referred to a designated hospital, 100 were infected asymptomatic patients, and 274 patients had mild COVID-19. ResultsThe vaccination rates (including fully and boosted) in the asymptomatic and mild COVID-19 patients were 92.00% and 94.16%, respectively. Majority of the studied population showed a first reverse transcription-polymerase chain reaction cycle threshold (Ct) value of 20. For 2565 nasopharyngeal swabs from close or sub-close contacts, the Ct value gradually increased to 35 for 8 days, and the median duration of viral shedding time was 10 days after the first positive detection of the SARS-CoV-2 nuclei acid. ConclusionsQuantitative viral RNA load assays in COVID-19 (BA.2.2.1) close or sub-closed contacts could be used to prevent transmissions and control precautions.

We evaluated and compared the diagnostic performance of fluorescence immunoassay (FIA) and two types of serological diagnostic tests: enzyme-linked immunosorbent assay (ELISA) and immunochromatographic assay (ICA) for detection of SARS-CoV-2 antigen and antibody to diagnose COVID-19 infections. This study is aimed to analyze and compare the current status and problems of COVID-19 diagnosis and various alternative diagnostic methods that are viable. The enrolled subjects in our study population were tested with real-time polymerase chain reaction (RT-PCR). ELISA and immunochromatographic diagnostic kit were used to diagnose 362 positive and 3010 negative SARS-CoV-2 specimens, and antigen fluorescence immunoassay kit was used on 62 positive and 70 negative SARS-CoV-2 RT-PCR confirmed samples for diagnosis. As a result, categorizing by the patient symptom onset days, PCL COVID19 Total Ab EIA (ELISA) showed the sensitivity of 93.4% from 15 to 21 days, 94.2% from over 22 days, and the specificity of 99.97%. PCL COVID19 IgG/IgM Rapid Gold (ICA) had a sensitivity of 86.9%, 97.4%, and the specificity of 98.14% respectively. PCL COVID19 Ag Rapid FIA sensitivity was 93.8% from 0 to 7 days, 71.4% from 8 to 12 days and specificity was 98.57%. In conclusion, COVID-19 Ab ELISA and ICA, and COVID-19 Ag FIA are all complementary and applicable diagnostic methods to resolve the current problems of COVID-19 diagnosis.

The 2020/2021 seasonal influenza vaccination was carried out under unique situations during the coronavirus disease 2019 (COVID-19) pandemic. Examining the factors affecting vaccine inoculation in a pandemic situation may provide valuable insights. The purpose of the current study was to investigate how the COVID-19 pandemic affected the 2020/2021 seasonal influenza vaccine intake. A cross-sectional study was conducted on workers aged 20-65 years on December 22-25, 2020, using data from an Internet survey. We set the presence or absence of 2020/2021 seasonal influenza vaccination as the dependent variable, and each aspect of sociodemographic factors, including gender, age, marital status, education, annual household income, and underlying disease, as independent variables. We performed a multilevel logistic regression analysis nested by residence. In total, 26,637 respondents (13,600 men, 13,037 women) participated, and a total of 11,404 individuals (42.8%) received the 2020/2021 influenza vaccine. Significantly more women than men were vaccinated, and the vaccination rate was higher among younger adults, married people, highly educated people, high-income earners, and those with underlying disease. The current results suggested that the relationship between seasonal influenza vaccination behavior and sociodemographic factors differed from the results reported in previous studies in terms of age. These findings suggest that, during the COVID-19 pandemic, young people may have become more aware of the risk of contracting influenza and of the effectiveness of the influenza vaccine. In addition, information interventions may have had a positive effect.

The exact pathology of COVID-19 remains mostly unclear, and accurate epidemiological understanding and rapid testing are crucial to overcome this disease. Several types of nucleic acid tests (NAT) have been used in Japan, but information about the viral RNA load, determined by Ct values, of the patients is limited due to the small number of patients tested in each clinical institution and lack of standardization of the testing kits. We have been performing the qRT-PCR tests established by NIID, and the mean Ct value distribution of 62 cases, which are deemed "first-visit" patients, among the total of 88 positive cases tested in a 4-day window of early April, was 24.9 with SD=5.45. Recently approved antigen testing kits were also used in the same samples (62 positives) along with 100 negative cases, and it revealed the positive predictive value of 80.6% and negative predictive value of 100%, with an overall agreement rate of 92.6%. These results indicate that a certain number of patients with lower Ct values, existed in Japan when SARS-CoV-2 virus started to spread. The newly approved rapid antigen testing kit will be a useful tool to identify such populations rapidly.

The Tokyo 2020 Olympic Games (Games) were held during the height of the coronavirus disease 2019 (COVID-19) pandemic. In order to detect the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) early enough to contain the spread as well as to facilitate the timely arrival of athletes at their game venues, all participating athletes up to 14,000 staying in the Olympic Village were screened daily for the infection. Toward this aim, a two-step strategy was adopted comprising screening of self-collected saliva samples using a chemiluminescence enzyme immunoassay followed by confirmatory testing using polymerase chain reaction. The testing system was integrated with an information management system covering all steps. To ensure the accuracy of testing results, rigorous quality assurance measures and monitoring of performance/specimen quality were implemented. The chronological chart analysis was implemented to monitor the holistic process and to give feedback to improve the sampling. Nearly all test results for 418506 saliva samples were reported within 12 hours of sample collection, achieving the target mean turnaround time of 150 minutes for confirmatory testing. As a result, athlete activity and performance for the Games were ensured. The chronological chart confirmed that no athletes were retired due to a false-positive result and no infection clusters among athletes were identified. In conclusion, continuous quality improvement in the two-step strategy for the large-scale screening of COVID-19 contributed to the success of the Games during the pandemic. The quality practice, systems, and workflows described here may offer a model for future mass-gathering sporting events during similar major infectious disease epidemics.