Japanese Journal of Infectious Diseases (2025)

We assessed case fatality rates (CFRs) in adults aged ≥70 years in 10 prefectures in Japan (14.8 million residents) diagnosed between January 2022 and March 2023, when the Omicron variant was dominant in Japan. We selected incident reports on 283,052 cases from participating public health centers reported according to the Infectious Diseases Control Law. Patients were passively followed up until the end of their isolation, date of death, or 28 days after COVID-19 diagnosis, whichever occurred first. We calculated age-standardized CFRs with 95% confidence intervals (CIs) using the Japanese population aged 70–79, 80–89 and ≥90 years in 2022, divided into 16 subgroups according to the period of COVID-19 diagnosis. The overall CFR was 1.59% (95% CI: 1.55–1.64%); ranging between 0.67% (95% CI: 0.38–0.96%, from May 23 to June 19, 2022) and 2.58% (95% CI: 2.36–2.80%, from January 31 to February 27, 2022). The age-standardized CFRs had three peaks, (2.2% from January 31 to February 27, 2022; 1.0% from July 18 to August 14, 2022; and 1.6% from December 26, 2022 to January 22, 2023) coinciding with the 6th, 7th, and 8th COVID-19 waves in Japan caused by the Omicron variant. Population-based CFRs for Omicron variant COVID-19 in adults aged ≥70 years remained <3% throughout the period January 2022 to March 2023, including during three large waves in Japan.

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We estimated the seroprevalence of anti-severe acute respiratory syndrome coronavirus 2 (anti-SARS-CoV-2) immunoglobulin G (IgG) in different island groups in Okinawa. A cross-sectional serosurvey was conducted over three periods between July 2020 and February 2021. A total of 2,683 serum samples were collected from six referral medical centers, each covering a separate region in Okinawa. In the main island, the seroprevalence was 0.0% (0/392; 95% confidence interval (CI), 0.0– 0.9%), 0.6% (8/1,448, 0.2–1.1%), and 1.4% (8/582, 0.6–2.7%) during the 1st, 2nd, and 3rd serosurvey, respectively. In remote islands, the seroprevalence was 0.0% (0/144; 95% CI, 0.0–2.5%) and 1.6% (2/123, 0.2–5.8%) during the 2nd and 3rd survey, respectively. The case detection ratio was 2.7 (95% CI, 1.3–5.3) in the main island and 2.8 (0.7–11.1) in remote islands during the 3rd survey. The case detection ratio was the highest in individuals aged 20–29 years (8.3; 95% CI, 3.3–21.4) in the main island and in those aged 50–59 years (14.1; 2.1–92.7) in remote islands, suggesting underreporting of clinical cases by the surveillance system in these subgroups. A serosurvey conducted during an emerging infectious disease epidemic can be useful for validating the reliability of the surveillance system by providing case detection ratio.

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Escherichia albertii is an emerging foodborne pathogen that causes diarrhea. Although various animals, especially poultry, serve as reservoirs of E. albertii, the transmission of E. albertii among reservoirs and the associated risks to humans remain unclear. This study investigated an E. albertii-infected infant exposed to poultry, and collected samples from contact persons, poultry, and the environment to better understand the transmission dynamics of E. albertii. One E. albertii isolate from a contact person, seven isolates from poultry, and six isolates from the environment were recovered. Whole-genome sequencing analysis showed that eight strains derived from poultry or environment and classified as ST4633 shared great similarity (core genome single-nucleotide polymorphisms [cgSNPs] ≤20). However, the patient-derived strain ESA311 had a cgSNP difference of 1165 with the human strain ESA339 and differed from poultry and environmental strains (cgSNP range 2417–14997), indicating distant relatedness. The whole-genome phylogeny showed that several human-derived E. albertii strains clustered with those of animal origin. Our results suggest that family-bred poultry constitute a possible reservoir for E. albertii, with the environment acting as a crucial vector for the spread of these bacteria and posing a risk to humans. Further surveillance of poultry is required to elucidate the public health risks associated with E. albertii infections.

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This study aimed to understand the clinical characteristics of severe fever with thrombocytopenia syndrome (SFTS) and identify the risk factors for prognosis. In this retrospective study, we collected epidemiological, demographic, clinical, and laboratory data from 101 patients with SFTS. Patients were divided into survival and deceased groups, and a logistic regression model was used to evaluate the association between the predictors and prognostic variables. A joint detection factor model was constructed, and a receiver operating characteristic curve was drawn. A nomogram was established using the R language, and its efficiency in diagnosing SFTS was evaluated using a calibration curve. Patients in the deceased group were more likely to be older, have a shorter hospitalization stay, and have renal and multiple organ failure than those in the survival group. Statistically significant differences were observed in the neutrophil percentage, lymphocyte percentage, neutrophil-to-lymphocyte ratio, platelet (PLT) count, aspartate aminotransferase (AST)/alanine transaminase (ALT) ratio, AST, blood urea nitrogen, lactate dehydrogenase, hydroxybutyrate dehydrogenase, thromboplastin time, and activated partial thromboplastin time between the two groups. Lymphocyte percentage, PLT count, and the AST/ALT ratio were independent risk factors for mortality in patients with SFTS. Thus, we established a prediction model for SFTS mortality with good efficiency.

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Dengue viruses enter the dermal macrophages derived from other tissues following a bite from an infected mosquito. We examined the chemotactic activity of factors derived from the dengue vector mosquito Aedes albopictus on a RAW264 murine macrophage cell line. We found that Elizabethkingia anophelis isolated from the mosquitoes exhibits migration-inducing activity in RAW264 cells. The active substances that induce the chemotactic movement were extracted using ethyl acetate. Chemotactic activity was noted in several of the fractions isolated using reverse-phase chromatography, suggesting that multiple components were responsible for this activity. Next, we isolated three bacterial colonies from wild A. albopictus mosquitoes collected from Toyama Park (Tokyo, Japan). The bacterial 16S rRNA gene sequences shared homology with that of Lonsdalea quercina. These bacteria also exhibited migration-inducing activity in RAW264 cells. The migration-inducing activity of the bacteria in mosquitoes may be a novel aspect of mosquito-mediated viral infections.

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Clostridium perfringens, which produces C. perfringens enterotoxin (CPE), is a major cause of food poisoning because of its gastrointestinal toxicity. In outbreaks of C. perfringens, genotyping is important for identifying the source. We genotyped strains isolated from an outbreak of food poisoning in Toyama Prefecture in 2023, using single-nucleotide polymorphism (SNP) analysis. The strains of C. perfringens were isolated from samples of curry consumed by all the affected patients and from the feces of patients and staff worker. The enterotoxin gene (cpe) was detected in isolates from patients and curry samples. The cpe-negative isolates were found in patients who had consumed curry and in the staff worker. The results of the SNP analysis suggested that the patient and curry isolates were likely from the same source but were unlikely to be related to the staff isolates. The results of SNP and pulsed-field gel electrophoresis (PFGE) analyses were consistent, indicating that the patient and curry isolates originated from the same source. SNP analysis, a whole-genome-based genotyping method, is a promising alternative to traditional PFGE for investigating outbreaks. Further studies are needed to accumulate more experience with genotyping using SNP analysis for the epidemiological investigation of outbreaks of C. perfringens.

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In Japan, as elsewhere, the coronavirus disease 2019 (COVID-19) pandemic has affected notification trends of respiratory syncytial virus (RSV) infection. Here, we describe the epidemiological trends of cases of RSV infection among children reported during 2018–2021 in Japan based on the national surveillance system. Compared with 2018 and 2019, 2020 saw an unprecedented decrease in notifications of RSV infection per sentinel site. However, 2021 experienced an unseasonably early and high peak at week 28 (peak week in 2018 and 2019 was week 37), with a large resurgence in notifications nationwide and across regions. Regarding age, compared with 2018 and 2019, the number and proportion of case-patients aged 2, 3, and ≥4-years increased substantially in 2021, but the number of case-patients aged <1 year decreased slightly. Furthermore, in 2021, the ratio of notifications per site from outpatient clinics to notifications per site from hospitals increased, suggesting a proportionate increase in diagnoses of clinically milder cases. Notably, RSV-attributed deaths from vital statistics also dropped substantially in 2020 and rebounded in 2021 but were fewer than in 2018 or 2019. While the incidence of RSV infections likely declined in 2020 (possibly owing to COVID-19 countermeasures) and increased in 2021, notifications in 2021 appeared to be associated with milder presentations. Given the unpredictable epidemiology of RSV, continuous monitoring and pluralistic assessments are imperative.

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