A Japanese man in his 50s who had lived in high-altitude rural areas, including the Tibet Autonomous Region, Qinghai Province and western Sichuan Province in China, Mongolia, and northern India, for more than 25 years presented with abdominal distension. Imaging studies revealed a cystic lesion in the left hepatic lobe with a 15-cm diameter and water lily sign consistent with cystic echinococcosis (CE) stage CE3a according to the World Health Organization Informal Working Group on Echinococcosis classification. Serum Western blotting detected antigen bands (7 kDa and 17 kDa), thus supporting the diagnosis of CE. Laparoscopic left hepatectomy was performed after initiation of albendazole therapy. Histopathological findings were compatible with a hydatid cyst. An analysis of mitochondrial genes extracted from cyst wall tissue identified Echinococcus granulosus sensu stricto genotype G3, thus confirming the diagnosis of CE. This case highlights the importance of integrating a detailed travel history, imaging studies, serological testing, and molecular analysis when diagnosing imported CE in nonendemic countries such as Japan.

Cholera is an infectious disease caused by Vibrio cholerae which has caused several global pandemics since 1817. Currently, Japan is not a cholera-endemic country, and only a few cases of imported disease are reported annually. Vibrio cholerae is classified into more than 200 serogroups according to the differences in the O antigen on the cell surface, and only the O1 or O139 groups that produce cholera toxins are called cholera.We report a case in which toxigenic Vibrio cholerae O1 was detected in a 64-year-old Japanese traveler returning from Delhi, India, who presented with diarrhea without rice-water stools. Multiple potential diarrheal pathogens were simultaneously detected, including Clostridioides difficile toxin A/B and pathogenic Escherichia coli (E. coli) including enteroaggregative, enteropathogenic, and enterotoxigenic E. coli, making definitive attribution of symptoms to a single pathogen difficult by Genetic testing (BioFire FilmArray Gastrointestinal Panel).This case highlights the diagnostic uncertainty that arises with multiplex PCR-based stool testing: while such panels improve detection sensitivity, distinguishing true infection from colonization remains a clinical challenge. Clinicians should integrate laboratory findings with travel history and clinical course rather than relying solely on molecular test results.

Introduction Older adults are at an increased risk of influenza-related hospitalisation and mortality due to a combination of risk factors. Severe influenza and excess mortality in this population remain major public health concerns, underscoring the need for novel treatment strategies.Methods and analysis This multicentre, investigator-initiated, randomised, double-blind clinical trial evaluated the efficacy and safety of the investigational drug favipiravir injection (T-705IV) in combination with oseltamivir phosphate, compared with oseltamivir monotherapy in hospitalised patients with influenza aged ≥65 years. Both T-705IV and oseltamivir phosphate will be administered for 5 days. The primary endpoint is time from randomisation to recovery within 15 days. Recovery is defined as either actual hospital discharge or sustained clinical status permitting discharge for 3 consecutive days. Clinical status will be assessed using a 7-point ordinal scale based on hospitalisation status and oxygen requirement. The primary analysis employs a Bayesian Cox proportional hazards model with a non-informative prior to estimate the posterior probability that the HR exceeds 1.0. The secondary endpoints include the distribution of 7-point scale scores over a 29-day period; rates of clinical worsening at days 15 and 29; duration of fever; all-cause mortality; intensive care unit admission within 29 days; pneumonia complication rate at 15 days; and changes in viral titre and viral RNA load on days 1, 2, 3 and 7. Safety will be assessed through the collection of adverse events (AEs) up to day 29. Pharmacokinetic evaluation will include measurement of plasma favipiravir concentrations on day 3. The planned sample size is 80 patients (40 per group).Ethics and dissemination Written informed consent will be obtained from all participants. This study was approved by the Center Hospital of the National Center for Global Health and Medicine Institutional Review Board (approval number: NCGM-I-022-24a) and registered in the Japan Registry of Clinical Trials. Study findings will be disseminated through peer-reviewed publications and/or presentations at academic conferences.Trial registration number jRCT2031240586,

Gram staining provides rapid microbiological information that may assist in empirical antimicrobial selection; however, the results are often interpreted by microbiological specialists who are not always available. Therefore, we developed a computer-aided diagnosis system using artificial intelligence trained on microscopic images of Gram-stained urine, captured with an iPhone, using the Bartholomew and Mittwer method. The system interprets Gram-stained urine samples and classifies bacterial morphology (Class 1: 7 predefined morphology categories) and 17 predefined species-level categories (Class 2). In this retrospective observational study, five imaging devices and two staining methods (Bartholomew and Mittwer, Favor) were compared. Urine specimens were collected from two hospitals between 1 April and 31 December 2022. Validation images were generated using five devices (four smartphones and one microscopic camera). We used a micrometer with microscopy with all smartphones; some iPhone images were taken without a micrometer. Favor staining was only imaged using an iPhone without the micrometer. Image data sets were generated from 433 clinical and 17 spiked samples. The overall accuracy was 0.804 for Class 1 and 0.640 for Class 2. Images taken by the microscopic camera had the highest accuracy and kappa coefficient, whereas the AQUOS smartphone had the lowest accuracy and kappa coefficient. The accuracy of images created without a micrometer was 0.885 for Class 1 and 0.666 for Class 2. The Bartholomew and Mittwer method had better accuracy and a better kappa coefficient. Overall, accuracy depended on the staining method used in the training data, not on the imaging device.IMPORTANCEGram staining provides rapid information on both the site of infection and likely pathogens, guiding empirical antimicrobial selection. However, interpretation requires infectious disease expertise, which is not always available. We developed an artificial intelligence-based diagnostic support system trained on iPhone images of Gram-stained urine using the Bartholomew and Mittwer method to classify bacterial morphology (Class 1) and inferred species (Class 2). To provide essential baseline data on factors influencing accuracy and reliability, we compared Gram-stained urine images from two hospitals obtained with five imaging devices and two staining methods. Microscopic camera images showed the highest accuracy, whereas an AQUOS smartphone showed the lowest. Images without a micrometer performed better, and the Bartholomew and Mittwer method outperformed the Favor method. Accuracy increased when confidence levels were higher. Our findings suggest that using the same staining method as the training data and avoiding micrometer noise are critical, while device differences are less influential.

INTRODUCTION:Fluoroquinolones (FQs) and trimethoprim-sulfamethoxazole (TMP-SMX) are first-line outpatient treatments for acute bacterial prostatitis (ABP). Owing to the increasing antimicrobial resistance and side effects of FQs and TMP-SMX, beta-lactams (BLs) are the recommended option; however, few reports have demonstrated the usefulness of oral BLs compared with FQs or TMP-SMX. Here, we evaluated the effectiveness of oral BLs compared with that of FQs and TMP-SMX after initial intravenous antibiotic therapy. PATIENTS AND METHODS:This single-center retrospective observational study included adult men with ABP who received intravenous antibiotic therapy and were subsequently switched to oral therapy. The causative organism was Enterobacteriaceae. The primary outcome was the clinical cure rate. The secondary outcomes included Clostridioides difficile infection, sepsis, and all-cause mortality within 30 days. RESULTS:Overall, 66 episodes in 65 patients met the eligibility criteria; 15 and 51 patients were included in the BL and FQ/TMP-SMX groups, respectively. Clinical cure was observed in 61.5% of the patients in the BL group and in 87.2% of the patients in the FQ/TMP-SMX group. A significant difference was observed for clinical cure with FQs/TMP-SMX (p = 0.049). However, this difference was not noted in the sensitivity analysis, and oral treatment duration between groups was suspected as a major confounder. No cases of C. difficile infection, sepsis, or all-cause mortality were observed. CONCLUSION:When initiating intravenous antimicrobial therapy for ABP and subsequently switching to oral antimicrobials, BLs may not demonstrate the same clinical effectiveness as FQs or TMP-SMX. Larger studies that adjust for background factors are necessary.

BACKGROUND:This randomized controlled trial provided LC16m8 pre-exposure prophylaxis to high-risk individuals to assess its efficacy for mpox prevention, safety, and immunogenicity. METHODS:This multicenter, randomized, open-label trial enrolled men and women aged ≥18 years at high risk of mpox. Participants were randomly assigned 1:1 to early- or late-vaccination groups. The primary endpoint was vaccine efficacy (VE) against mpox. Secondary endpoints included VE against severe mpox, symptoms, "take" incidence, adverse events (AEs), and immunogenicity in participants with human immunodeficiency virus (HIV). RESULTS:In total, 570 and 565 participants were assigned to early- and late-vaccination groups, respectively, with 530 and 476 vaccinated. The median age was 41 years; 99.7% were male, 89.7% were Japanese, and 34.4% had HIV. No mpox cases occurred, precluding VE calculations. The take rates were 89.5% (with HIV) and 93.9% (without HIV). AEs occurred in 97.2% and 98.2% of participants with and without HIV, respectively. No fatal AEs were observed. Serious adverse events (SAEs) were observed in 2/352 (0.6%) and 3/654 (0.5%) of participants with and without HIV, respectively, of which 1 SAE causally related to vaccination occurred in a participant without HIV. Seroconversion rates for LC16m8 and MPXV were 96.2% and 69.2%, respectively, in participants with HIV, and 92.0% and 52.0%, respectively, in individuals without HIV. CONCLUSIONS:LC16m8 efficacy in mpox remains inconclusive. However, in individuals with well-controlled HIV, it was immunogenic and raised no significant safety concerns, suggesting its suitability for targeted vaccination of at-risk groups. (Japan Registry of Clinical Trials number, jRCT1031230137).

Mycobacterium abscessus is a rapidly growing nontuberculous mycobacterium that causes extrapulmonary infections, including surgical site infections. Mycobacterium abscessus subsp. abscessus (MAA) frequently develops macrolide resistance, resulting in difficult-to-treat infections. Recently, surgical site infections caused by MAAs after cosmetic surgeries have become a notable concern, particularly as the number of cosmetic surgery clinics in Japan continues to increase. Therefore, vigilance for MAA infections following cosmetic procedures is necessary. However, reports on the treatment of macrolide-resistant MAA are limited. We report a case of surgical site infection following cosmetic surgery caused by macrolide-resistant MAA. A 47-year-old woman developed subcutaneous erythema, induration, and fistula formation several months after a thread lift procedure. Exudate culture revealed MAA harboring a full-length erm41 gene associated with inducible macrolide resistance, and susceptibility testing confirmed macrolide resistance. Treatment was initiated with combination antimicrobial therapy, including imipenem/cilastatin, amikacin, and tigecycline for 4 weeks, followed by clofazimine and sitafloxacin for 11 months as maintenance therapy. Local debridement was performed; however, complete removal of the threaded material was not feasible because thread had dissolved. After 12 months of treatment, the fistula closed, and no recurrence occurred during follow-up. This case highlights the importance of considering MAA in surgical site infections following cosmetic surgery and suggests that individualized combination antimicrobial therapy based on susceptibility testing may lead to successful outcomes in macrolide-resistant extrapulmonary MAA.

INTRODUCTION:The importation of infectious diseases has increased dramatically in recent years. The diagnosis of such diseases has traditionally been based on symptoms, as well as blood and biochemical tests. In this study, we developed machine-learning models to diagnose influenza cases among international travellers using information on the number of infected individuals in destination countries and the incubation period, which have not been utilised for diagnosis. METHODS:This study examined cases recorded in Japan Registry for Infectious Diseases from Abroad (https://jrida-jprecor.ncgm.go.jp/en/j-rida/index.html), which included influenza test results and information on travel destination and duration. Multivariable logistic regression and machine-learning methods were used to build diagnostic models, with symptoms and an epidemiological score calculated from information on the number of cases in the destination country and the incubation period serving as explanatory variables. RESULTS:Logistic regression analysis revealed that symptoms such as fever (p < 0.001) and cough (p < 0.001), as well as the epidemiological score (p < 0.001), were significant predictors of influenza infection. The machine-learning models were then developed and tested using training and test data, respectively. The constructed models showed good specificity and high accuracy. Among these models, the neural network had the highest accuracy (93%). DISCUSSION:Adding epidemiological information to the usual clinical information can improve diagnostic accuracy. Machine-learning models capable of handling a wide variety of data would be particularly beneficial for diagnosis. The knowledge gained should also be used to raise awareness among travellers.

Gram staining is one of the basic tests to identify the organism in microbiological laboratory, especially in blood culture. However, microbiological specialists are not always available, which can lead to treatment delays. Therefore, we developed a computer-aided diagnosis (CAD) system that uses artificial intelligence to predict causative pathogens from Gram-stained blood culture images, focusing on both morphological (Class 1) and detailed (Class 2) classification. In this retrospective observational study, we compared the accuracy of predictions made by microbiology specialists (MS) and by CAD using iPhone-captured images of clinical samples stained with the Bartholomew and Mittwer method collected from two tertiary care hospitals between 1 October 2022 and 31 January 2023. Among 126 samples (378 images) for aerobic bottles (AE) and 90 samples (270 images) for anaerobic bottles (AN), the accuracy of MS and CAD prediction (95% confidence interval) was 91.5% (90.5%-92.3%) and 75.4% (70.7%-79.7%) for AE and 90.1% (88.9%-91.2%) and 76.7% (71.2%-81.6%) for AN, respectively. Although we could not demonstrate non-inferiority, most of the mispredictions occurred with Gram-negative cocci, Haemophilus influenzae, and Campylobacter spp., while relatively good results were obtained for other species. CAD has the potential to provide early diagnostic results and indicate timely treatment during off-hours and in medical facilities without microbiology specialists. On the other hand, it should be noted that certain bacterial species remain challenging for AI-based identification, and improving accuracy in these areas is an important task for future development. IMPORTANCE:Gram staining of a positive blood culture is essential for early diagnosis and appropriate antibiotic selection, but interpretation requires trained specialists, limiting rapid reporting. While artificial intelligence (AI)-based automation has been explored, most previous studies either focused on a limited range of bacterial species or evaluated only the performance of the device itself. Also, most systems rely on bulky equipment. To address this, we developed a mobile device-based computer-aided diagnosis system for Gram stain interpretation and conducted a non-inferiority trial comparing its accuracy with that of microbiology specialists. Although non-inferiority was not demonstrated, we identified bacterial species that the AI system had difficulty distinguishing. With an appropriate understanding of these limitations, AI-assisted Gram stain interpretation could help reduce turnaround time and support timely clinical decision-making.

Fluoroquinolones (FQ) and trimethoprim–sulfamethoxazole (TMP–SMX) are first-line therapies for acute bacterial prostatitis, but rising antimicrobial resistance and adverse events limit their utility. Evaluating the efficacy of oral β-lactams (BL) may expand available treatment options.Table.Patient Characteristics and Outcomes This retrospective study was conducted at the National Center for Global Health and Medicine, a tertiary hospital in Japan between 2013 and 2023. We included men aged 18 years or older who had received intravenous antimicrobial therapy for acute bacterial prostatitis based on medical records, were subsequently switched to oral therapy, and had Enterobacteriaceae as the cause. The primary endpoint was clinical cure, defined as improvement of symptoms, no recurrence of urinary tract symptoms within 30 days, no discontinuation or change of treatment due to worsening symptoms, and no adverse events. Secondary endpoints included Clostridioides difficile infection (CDI), sepsis, and all-cause mortality within 30 days of initiation of treatment. We compared the oral BL group with the FQ or TMP-SMX group (FQ/ST), receiving statistical analysis with AI support. Of 337 registered prostatitis cases, 71 met inclusion criteria. Seven patients were excluded: two received other drugs and five were lost to follow-up. Finally, 13 patients who received BL and 51 received FQ/ST were included in the analysis. Baseline characteristics were comparable between groups (Table 1). There was no significant difference in the primary endpoint between the BL and FQ/ST groups (odds ratio: 0.255, 95% confidence interval: 0.065-1.005, p=0.056). Secondary endpoints were also not different for sepsis between the two groups; CDI and all-cause mortality did not occur in either group. TMP-SMX was frequently discontinued due to adverse effects, whereas recurrence occurred in both FQ and BL, even with susceptible isolates. In this retrospective study, there was no significant difference between the two groups, which may be attributable to the small sample size. A potential advantage of the FQ/ST group might become apparent with a larger cohort. Further research should employ large sample sizes with rigorous adjustment for patient characteristics. All Authors: No reported disclosures

Abstract Background Since May 2022, the incidence of mpox cases has surged outside endemic regions. Although vaccination remains pivotal in mpox prevention, data on LC16m8, a third-generation smallpox vaccine, are scant. We provided LC16m8 pre-exposure prophylaxis opportunities to high-risk individuals, including those with HIV, and conducted a randomized controlled trial to assess LC16m8’s effectiveness in mpox prevention and safety. Methods Our multicenter randomized open-label trial enrolled men and women aged ≥18 years at high mpox risk who provided written consent. Participants were randomly assigned 1:1 to early or late vaccination groups, receiving vaccinations approximately 70 days apart. Primary endpoint: vaccine effectiveness (VE) against mpox development between early and late vaccinations. VE against severe mpox, symptoms, “take” incidence, and adverse events were secondary endpoints. Results A total of 1,135 participants were recruited; 570 and 565 were assigned to early and late vaccination groups, respectively; 530 and 476 were vaccinated. Median age: 41 years; 99.7% were male; 89.7% Japanese; and 34.4% HIV-infected. No mpox cases occurred during the observation period, precluding VE calculation. “Take” rates: 90.3% (HIV-infected), 94.6% (uninfected). Adverse events related to the study were observed in 96.6% and 98.0% of the HIV-infected and uninfected participants, respectively. No fatal adverse events were observed; serious adverse events (SAE): 0.6% (HIV-infected), 0.5% (uninfected). One HIV-uninfected participant reported pulmonary embolism and deep vein thrombosis as a causally undeniable SAE. Local skin reactions: 96.6% (HIV-infected), 97.9% (uninfected); systemic reactions: 63.6% (HIV-infected), 64.2% (uninfected). Conclusion LC16m8’s effectiveness in mpox prevention remains inconclusive. Yet, its use in well-controlled HIV-infected and -uninfected individuals showed no significant safety concerns, suggesting potential for targeted vaccination strategies in at-risk groups. Disclosures All Authors: No reported disclosures

Introduction. Timely and accurate diagnosis of bacterial infections enables early administration of appropriate antimicrobial treatment and improved outcomes. Hypothesis/Gap Statement. The accuracy of computer-aided diagnosis (CAD) for identifying organisms on urine Gram stains has not been compared with that of microbiology specialists (MS). Aim. To compare the interpretation of urine Gram-stain results by MS and a CAD app designed using artificial intelligence. Methodology. Urine specimens from patients with urinary tract infections were used and collected at two tertiary hospitals between 1 April and 31 December 2022. Using non-inferiority analysis to assess whether CAD was non-inferior to expert interpretation, CAD-predicted microscopic findings of the Gram-stained slide generated from iPhone camera images from two hospitals were compared with those from ten MS. A total of 153 images were taken from each hospital, and CAD interpreted a total of 306. The primary endpoint was the prediction accuracy based on the morphology of the Gram-stained bacteria. Results. The accuracy (95% confidence interval) of MS and CAD predictions was 83.0% (81.6%–84.3%) and 87.9% (83.7%–91.3%), respectively, with a difference of –4.93% (–8.43% to –0.62%) indicating non-inferiority of CAD. Conclusion. CAD was non-inferior to MS predictions for identifying Gram-stained pathogens; therefore, CAD was suggested to have the potential for guiding empirical antibiotic selection in patients with urinary tract infections.

End-of-life decision making regarding invasive mechanical ventilation (IMV) for patients with severe coronavirus disease (COVID-19) is challenging. We aimed to explore the factors associated with the withholding of IMV in patients with COVID-19. This retrospective study included patients registered in a nationwide COVID-19 Registry Japan. We enrolled patients with COVID-19 admitted between January 1, 2020, and June 30, 2021, and died during hospitalization. The enrolled patients were divided into two groups: those who received IMV (IMV group) and those who did not (non-IMV group). To identify the factors associated with withholding of IMV among patients with COVID-19 who died during hospitalization, we conducted a multivariate logistic regression analysis. A total of 2,401 patients were enrolled. Of these, 588 (24.5%) were in the IMV group and 1813 (75.5%) in the non-IMV group. Withholding IMV was positively associated with older age (95% confidence interval [CI]: 0.82-0.88, p < 0.0001), dementia (95% CI: 0.81-0.91, p < 0.0001), chronic lung disease (95% CI: 0.88-1.00, p = 0.036), and malignancy (95% CI: 0.82-0.94, p < 0.0004) although inversely associated with male sex (95% CI: 1.04-1.15, p = 0.0008), body mass index (95% CI: 1.01-1.02, p < 0.0001), and National Early Warning Score (95% CI: 1.01-1.03, p < 0.0001). We subsequently analyzed these results to inform preparedness for future emerging infectious disease pandemics by retrospectively examining the decision-making processes during the COVID-19 crisis, with particular attention to the role of multidisciplinary collaboration. Based on this study, it will be essential in future pandemics to assess decisions concerning life-sustaining treatments, including IMV, from both scientific and ethical perspectives.

A 30-year-old Japanese man who traveled to the Republic of Ghana was diagnosed with falciparum malaria while undergoing chemotherapy for acute leukemia in Japan. We considered him to be at high risk of severe disease; however, he showed no signs of severe malaria and was treated with 3 days of oral artemether/lumefantrine. The patient's medical history may have contributed to the suppression and successful treatment of falciparum malaria without severe complications.

This perspective article outlines Japan’s contributions to strengthening the global health emergency workforce through the Global Outbreak Alert and Response Network. It highlights Japan’s strategic initiatives in training, expert deployment and institutional collaboration, underscoring how national efforts can enhance global health security.

Background: Cefmetazole (CMZ) is a carbapenem-sparing option in the treatment of extended-spectrum betalactamase (ESBL)-producing bacterial infection. In this pilot study, we aimed to compare the effects of antimicrobial treatment (meropenem [MP] and CMZ) with those of no antimicrobial treatment (control group) on the microbiome. Methods: The study was a multicenter, prospective, observational pilot study conducted from October 2020 to October 2022. Feces and saliva samples were collected for microbiome analyses at two time points (early-period: days 1-3; and late-period: days 4-30) for the antimicrobial treatment group, and at one time point for the control group. Results: Five feces (MP-F and CMZ-F) and five saliva (MP-S and CMZ-S) samples were included in the MP and the CMZ groups. Ten feces (C-F) and saliva (C-S) samples were included in the control group. Group alpha diversity was notably lower in the late-period MP-F group than the control group as determined with the Shannon richness index. beta diversity analysis of the feces samples based on weighted and unweighted UniFrac distances revealed distinctions in both the late-period CMZ-F and MP-F groups compared with the control group. Weighted UniFrac analysis showed that only the early-period MP-F group differed from the control group. In the saliva samples, weighted and unweighted UniFrac analyses showed significant differences between the control group and the early CMZ, late CMZ, and late MP groups. Conclusions: MP treatment may cause larger impact on the feces microbiome than CMZ in Japanese patients.

International travel is a risk factor for acquiring sexually transmitted infections (STIs) owing to factors such as increased sexual opportunities, a sense of freedom, and the allure of the sex industry. We investigated the incidence of travel-associated STIs in Japan using data from the Japan Registry for Infectious Diseases from Abroad (J-RIDA) reported by 17 participating medical institutions between October 2017 and December 2022. Data were collected on the patients' age, sex, nationality, chief complaint, whether they had visited a travel clinic before travel, travel history, and final diagnosis. Of 4545 cases of travel-associated illness reported, 52 (1.1%) were STIs. Most patients with STIs were male (81%) with a median age of 31 years. HIV (17%), genital herpes (13%), syphilis (13%), and gonorrhea (12%) were the most frequently reported STIs. Only one patient had visited a travel clinic before travel. Promoting awareness and vaccination is crucial for preventing travel-associated STIs.

Background Dexamethasone is currently administered for Coronavirus disease 2019(COVID-19); however, there are concerns about its effect on specific antibodies’ production. The aim of this study was to evaluate whether specific antibodies were affected by COVID-19 severity and corticosteroid treatment. Methods Of 251 confirmed COVID-19 patients admitted to our hospital between January 26 and August 10, 2020, the early period of the pandemic, 75 patients with sera within 1 month of onset and 1month or longer were included in the research. A total of 253 serum samples from these patients were collected. The levels of specific antibodies for severe acute respiratory syndrome coronavirus 2(SARS-CoV-2), immunoglobulin G (IgG) and M (IgM), were measured retrospectively. The results were compared separately of each COVID-19 severity, and with or without corticosteroid treatment. Results Among the 75 patients, 47, 18, and 10 had mild, moderate, and severe disease, respectively. The median age was 53.0 years and 22 (29%) were women. The most common comorbidities were hypertension and dyslipidemia. Corticosteroids were administered to 20 (27%) and 10 (53%), patients with moderate and severe disease, respectively. The positivity rates IgM increased first, and IgG was almost always positive after day 16, regardless of the severity of COVID-19. On days 6–10, both IgG and IgM positivity rates were higher in patients with moderate disease than in those with mild or severe disease. In patients with moderate disease, IgG positivity was similar over time, regardless of corticosteroid treatment. Conclusions In COVID-19 patients, specific IgG is positive and maintained for a long period of time, even after corticosteroid treatment. The effect of corticosteroid treatment in a COVID-19 epidemiological study using specific IgG antibodies was considered minor. COVID-19 patients were more likely to receive oxygen if IgM was positive 1 week after onset, but not mechanical ventilation. IgM measurement 1 week after onset may predict COVID-19 severity.

Background: To date, few studies from the Asian region have reported the effectiveness of messenger ribonucleic acid coronavirus disease 2019 (COVID-19) vaccines against disease progression and death after hospitalization. Methods: We evaluated the data from the COVID-19 registry in Japan during the delta- and omicron-dominant phases. A propensity score-matched cohort study was conducted between the incompletely (0-1 dose) and fully (2 doses) vaccinated groups during the delta-dominant phase and among the incompletely, fully, and booster (3 doses) vaccinated groups during the omicron-dominant phase. Results: In the delta-dominant phase, 411 pairs were matched. The fully vaccinated group showed a significantly lower oxygen supplementation rate (24.1 % vs. 41.1 %, p < 0.001) but little difference in the mortality rate (2.2 % vs. 2.9 %, p = 0.66). In the omicron-dominant phase, 1494 pairs from the incompletely and fully vaccinated groups, and 425 pairs from the fully and booster vaccinated groups were matched. Full vaccination reduced both the oxygen supplementation rate (18.6 % vs 25.7 %, p < 0.001) and mortality rate (0.7 % vs 2.3 %, p < 0.001). Booster vaccination showed little difference in either the rate of oxygen supplementation (21.2 % vs. 24.7 %, p = 0.25) or mortality (1.2 % vs. 2.6 %, p = 0.21) compared with full vaccination. Conclusions: Full vaccination reduced disease severity during the delta- and omicron-dominant phases; booster vaccination did not further enhance the protective effects against disease progression during the omicron-dominant phase compared to full vaccination. Future vaccine strategies and policy decisions should consider preventing infection or disease progression in the target population, as well as the characteristics of the dominant variant in that phase. Copyright (c) 2023, Taiwan Society of Microbiology. Published by Elsevier Taiwan LLC. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/ 4.0/).