A localized pertussis outbreak involving 10 unvaccinated infants occurred in Kumamoto, Japan, during March-May 2025. Nine infants were admitted to the pediatric intensive care unit, 6 of whom received a confirmed diagnosis of macrolide-resistant Bordetella pertussis infection. This outbreak highlights the importance of booster vaccinations and resistance surveillance.

Periodontal disease has been associated with adverse pregnancy outcomes, but evidence regarding the association between psychoactive substance use and periodontal pathogens during pregnancy remains limited, particularly in low-resource settings. This study examined the association between psychoactive substance use and salivary periodontal pathogen levels among pregnant women in rural Rwanda. This cross-sectional study was a secondary analysis of baseline data from a pregnancy cohort conducted in 2019 at a district hospital in Rwanda. A total of 178 pregnant women participated. Demographic characteristics, oral health behaviors, and psychoactive substance use were assessed using structured questionnaires. Salivary DNA copy numbers of four periodontal pathogens were quantified by quantitative real-time polymerase chain reaction, and associations were evaluated using multivariable generalized linear models. Women with a history of alcohol consumption before pregnancy had significantly higher levels of Tannerella forsythia than women who had never consumed alcohol (fold change 4.78, p = 0.006). Women with a history of drug use before pregnancy had significantly lower levels of Prevotella intermedia (fold change 0.29, p = 0.011), while women with a history of dental visits had significantly lower levels of Porphyromonas gingivalis (fold change 0.04, p = 0.014). These findings suggest that pre-pregnancy lifestyle factors and oral health behaviors are associated with the maternal oral microbial environment during pregnancy. However, because of the cross-sectional design, causal relationships and their potential implications for maternal and pregnancy outcomes could not be determined. Further longitudinal and mechanistic studies are warranted to clarify these associations and their potential clinical significance.

BACKGROUND:Early-life respiratory infections are associated with subsequent asthma development; however, whether respiratory viruses contribute to asthma onset or merely unmask pre-existing susceptibility remains unclear. The COVID-19 pandemic's non-pharmaceutical interventions (NPIs) suppressed respiratory viruses, followed by their resurgence, offering a natural experiment. We examined whether these population-level changes in respiratory virus activity were associated with changes in newly recorded pediatric asthma diagnoses. METHODS:We conducted a nationwide interrupted time-series study using Japan's National Database of Health Insurance Claims, covering approximately 99% of the population. Segmented negative binomial regression with two intervention points-NPI implementation (T1: March 2020) and COVID-19 reclassification (T2: May 2023)-was applied to monthly counts of newly recorded asthma diagnoses among children aged under 19 years (January 2018-March 2024), with atopic dermatitis as negative control. Age-stratified/sex-stratified analyses and exploratory ecological analyses of pathogen-specific associations were conducted. RESULTS:Among 10,508,387 new asthma diagnoses, incidence declined significantly following NPI implementation (incidence rate ratio [IRR] 0.511, 95% confidence interval [CI] 0.422-0.620) and rebounded following NPI relaxation (IRR 1.395, 95% CI:1.120-1.737). Atopic dermatitis showed attenuated changes at both points. Rate differences were greatest in infants (0-1 years) at T1 and school-aged children (5-9 years) at T2. Rhinovirus, respiratory syncytial virus, influenza, and Mycoplasma pneumoniae, but not SARS-CoV-2, correlated with asthma diagnoses in ecological analyses. CONCLUSIONS:Newly recorded pediatric asthma diagnoses showed bidirectional changes that paralleled respiratory virus suppression and resurgence, compatible with a possible contributory role of respiratory infections, particularly among infants and school-aged children.

Studies examining small-for-gestational-age (SGA) infants and sleep timing during childhood are scarce. We investigated the association between infant SGA status and sleep timing (wake-up time and bedtime) at age of 2.5 and 7 years using data from a Japanese birth cohort study conducted from 2001 (n = 46,563). SGA was defined as birth weight below the 10th percentile for gestational age based on Japanese reference standards. The four sleep-timing outcomes were defined as wake-up time at or after 9:00 am or irregular and bedtime at or after 10:00 pm or irregular at 2.5 years, and wake-up time at or after 7:00 am or irregular and bedtime at or after 10:00 pm or irregular on school days at 7 years. These cut-off points were used as study-specific operational definitions based on the questionnaire response categories. Poisson regression with robust variance was used to estimate risk ratios (RRs) and 95% confidence intervals, adjusting for child and parental factors. In crude analyses, children born SGA had a slightly higher RR for bedtime at or after 10:00 pm or irregular at 2.5 years; however, this association was not significant after adjustment. No significant association was observed for the other outcomes. Sensitivity and stratified analyses yielded similar results.

BACKGROUND:Although participation in organised extracurricular activities has been associated with higher self-esteem, high participation frequency may have adverse effects, as proposed by the overscheduling hypothesis. Longitudinal evidence from non-Western countries is limited. We examined whether the frequency of enrichment-oriented out-of-school lessons (naraigoto) in fourth grade was associated with self-esteem in sixth grade in a Japanese large-scale cohort. METHODS:We analysed longitudinal data from the Japanese Longitudinal Study of Children and Parents from fourth grade (baseline, 2017-2019) to sixth grade (follow-up, 2019-2021) (n = 3399). The exposure was the frequency of enrichment-oriented activities in fourth grade, excluding academic tutoring (juku). The outcome was self-confidence in sixth grade (4-point Likert scale). Ordinal logistic regression models were employed for estimating odds ratios and 95% confidence intervals, and possible confounders (sociodemographic factors, baseline self-confidence) were adjusted. Sensitivity analyses were also conducted using alternative outcome and alternative exposure definitions. RESULTS:In the fully adjusted model, the adjusted odds ratios for higher self-confidence were 1.22 (95% confidence interval 0.96-1.55) for one session/week, 1.30 (1.02-1.66) for two sessions/week, 1.34 (1.04-1.73) for three session/week, 1.41 (1.10-1.82) for four to five sessions/week, and 1.22 (0.87-1.71) for six or more sessions/week, compared with zero sessions/week (reference). Associations were strongest at two to five sessions/week, with no increase at six or more sessions/week. Results were similar in sensitivity analyses. Gender-stratified analyses suggested that these associations were significant only in male participants. CONCLUSIONS:Enrichment activity participation was associated with self-esteem 2 years later, with the strongest associations at moderate frequencies. Future studies should examine total amount of time and qualitative aspects of participation.

Minamata disease, officially recognized in 1956, is a well-known food poisoning event that was caused by the consumption of fish and seafood contaminated with methylmercury. Although patients with congenital Minamata disease (CMD) with severe neurological impairments after birth are widely recognized, few studies have examined the effects of prenatal methylmercury exposure among residents, which is likely at lower levels than in CMD patients. We aimed to investigate the relationship between prenatal methylmercury exposure and subsequent neurological and neurocognitive outcomes. We conducted a cross-sectional study during 2024-2025 among 51 individuals aged approximately 70 years, 27 residents from an existing cohort established in 1970 in Minamata and 24 age-matched individuals who had lived in less-exposed regions. We performed a battery of neurological and neurocognitive tests in both groups and compared the results using multiple linear regression analyses. We also examined the association between intelligence scores obtained in 1970, and intelligence scores obtained in the present investigation, only among exposed participants. We found that exposed individuals had unfavorable neurological and neurocognitive test scores, in comparison with less-exposed controls. Scores on the Montreal Cognitive Assessment, Japanese Edition were 5.91 points lower (95% confidence interval: 3.09 to 8.73) for exposed residents than for the less-exposed group. Moreover, intelligence scores evaluated during exposed participants' adolescence were correlated with their neurocognitive scores in adulthood. Our findings showed that prenatal methylmercury exposure affected subsequent neurological and neurocognitive functions, including among individuals with lower exposure than in CMD patients, and even approximately 70 years after the initial exposure.

AIM:The COVID-19 pandemic had substantial effects on youth mental health. Most previous studies focused on the initial pandemic years, leaving the post-restriction period underexplored. We examined trajectories of newly recorded psychiatric diagnoses among Japanese youths across two policy shifts: March 2020 school closures and May 2023 reclassification of COVID-19 as an influenza-equivalent Category V disease. METHODS:We conducted an interrupted time-series analysis using the National Database of Health Insurance Claims, covering over 99% of the Japanese population. The study included 21 million individuals aged under 19 years to analyze monthly trends in first recorded psychiatric diagnoses from January 2018 to March 2024. Segmented negative binomial regression was used to estimate shifts in levels and trends following both policy interventions. RESULTS:Following the 2020 closures, eating disorders showed sex-specific patterns: males showed an immediate 28.8% decrease (IRR 0.712, 95% CI 0.619-0.819), whereas females showed a 28.4% increase (IRR 1.284, 95% CI 1.045-1.576). Newly recorded ADHD diagnoses showed an 8.1% immediate decrease (IRR 0.919, 95% CI 0.847-0.997). During the restriction period, anxiety/stress-related and mood disorders showed apparent surge patterns following infection waves. After restrictions were lifted in 2023, eating disorders among males showed an upward level shift (IRR 1.214, 95% CI 1.076-1.370). Neurodevelopmental disorders showed preliminary downward trends in the post-restriction period. CONCLUSION:This nationwide study of 21 million youths suggested differential diagnostic patterns across pandemic phases. These contrasting trajectories highlight the need for subgroup-level post-pandemic diagnostic surveillance.

The health effects of heat exposure may be pronounced during periods of seasonal temperature change but may attenuate over time. However, epidemiological studies quantifying the health effects of temperature during seasonal transitions remain limited. We investigated whether increases in Wet-Bulb Globe Temperature (WBGT) during the transition from the rainy season to summer were associated with the risk of cerebrovascular disease onset in Japan. We adopted a time-stratified case-crossover design using Utstein-style registry data from 2014 to 2023. We identified 5,638 out-of-hospital cardiac arrest cases due to cerebrovascular disease during the rainy season (Tsuyu period) and the subsequent five weeks. We used conditional logistic regression to assess the association between categorized WBGT levels at onset (0 h) and case occurrence. We also evaluated the effects of cumulative exposure. During the Tsuyu period, higher WBGT levels did not increase the risk of onset, whereas the rapid increase in WBGT immediately after the Tsuyu period elevated the risk of cerebrovascular disease events, with an odds ration of 4.75 (95% confidence interval: 3.01-7.49) at 28-30°C compared with the reference (<25°C). The risk gradually decreased over the 4–5 weeks following the Tsuyu period. We observed similar findings when we considered cumulative exposure. The risk patterns differed between age groups (≤65 and >65 years). In conclusion, an increase in WBGT immediately after the Tsuyu period elevated the risk of cerebrovascular disease onset. The risk remained high for 2–3 weeks before declining by week 5, likely as individual heat acclimatization progressed.

The proportion of people who have anti-nucleocapsid (N) protein antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been reported as a surrogate for the proportion of previously infected individuals. This seroepidemiologic survey, conducted from 6 November 2023 to 19 January 2024, aimed to measure the levels of anti-N protein antibodies produced in the body by SARS-CoV-2 among residents over 18 years of age in Bizen City, Okayama, Japan. We evaluated the prevalence of SARS-CoV-2 antibodies in the target population at the time of the investigation and assessed changes over time among participants who had previously been infected. Of the 444 participants, a total of 235 (52.9%) were infected within one year. The seroprevalence of participants testing positive remained above 80% until four months post-infection, after which the number of people who remained positive declined rapidly. Six months after infection, around 10% of participants tested positive for anti-N protein antibodies, and this seroprevalence remained the same for up to one year post-infection. We demonstrated that the anti-N protein antibodies test is useful for identifying recently infected individuals for several months post-infection. We showed that it becomes increasingly difficult to detect past infections as time elapses since infection.

The long-term effects of cesarean delivery (CD) on child health and development remain controversial. This study aimed to investigate these effects using an outcome-wide approach in a Japanese context, where perinatal mortality rates are among the world's lowest. We analyzed data from 2,114 children in a nationwide Japanese birth cohort, linking the 21st Century Longitudinal Survey of Newborns with the Perinatal Research Network database. We examined associations between CD and various health and developmental outcomes up to 9 years of age, including hospitalizations, obesity, and developmental milestones. After adjusting for potential confounders, CD was not significantly associated with most outcomes, including all-cause hospitalization (adjusted risk ratio 1.25, 95% CI 0.997-1.56), obesity at 5.5 and 9 years, and various developmental milestones. Subgroup analyses for multiple births and preterm infants showed some differences in point estimates, but were limited by small sample sizes. CD was not significantly associated with adverse long-term child health or developmental outcomes in this Japanese cohort. These findings provide reassurance regarding CD safety when medically indicated in advanced perinatal care settings. Further research with larger samples and longer follow-up is needed, especially for specific subgroups.

Abstract Background The incidence of allergic diseases has been increasing in Japan. In particular, a serious decline in the age of onset of allergic rhinitis has been observed. Passive smoking from parental smoking has a significant impact on children’s health; however, it is difficult to restrict smoking in the home. While various studies have previously reported on the relationship between passive smoking and the development of allergic diseases in children. However, there have been no reports on passive smoking and allergic diseases on a national scale. Methods Using Japanese national longitudinal survey data (n = 38,444) for newborns born between May 10 and 24, 2010, we assessed parental smoking habits when their children were 6 months old and investigated the association with the development of allergic diseases until the age of 5.5 years. The risk ratios and 95% confidence intervals for the development of different allergic diseases were analyzed after adjusting for potential confounders using Poisson regression with a robust error variance. Results The risk ratio for developing allergic rhinitis/allergic conjunctivitis (AR/AC) in children was significantly higher in the maternal smoking groups ( ≦ 10 cigarettes/day; RR 1.15, 95% CI 1.02–1.30; ≧11 cigarettes/day; RR 1.16, 95% CI 0.93–1.44). Furthermore, associations were found between the maternal smoking group in the presence of paternal smoking and the risk of developing bronchial asthma ( ≦ 10, RR 1.33 95% CI 1.17–1.52; ≧11, RR 1.71 95% CI 1.38–2.1), food allergy ( ≦ 10, RR 1.36 95% CI 1.12–1.63; ≧11, RR 1.25 95% CI 0.84–1.86), atopic dermatitis ( ≦ 10, RR 1.42 95% CI 1.22–1.66; ≧11, RR 1.6 95% CI 1.2–2.13), and AR/AC ( ≦ 10, RR 1.21 95% CI 1.07–1.36; ≧11, RR 1.35 95% CI 1.09–1.67). Conclusions Maternal smoking during infancy increases the risk of developing AR/AC in children. Considering paternal smoking, maternal smoking further increased the risk of developing allergic diseases in children, suggesting that reducing parental smoking at home may reduce the risk of developing allergic diseases in children.

OBJECTIVE:The aim of this study was to analyze nationwide patterns of epistaxis treatment in Japan, including temporal trends, demographic distributions, and regional variations. This was a nationwide descriptive observational study using a national administrative database. METHODS:We analyzed open data of the National Database of Health Insurance Claims from fiscal years 2019-2022 to examine two treatment procedures for epistaxis: hemostasis with gauze packing and cauterization. Treatment patterns were evaluated by month, age, sex, and prefecture of residence. The standardized claim ratio was calculated using indirect standardization for regional comparisons RESULTS: During the study period, 870,819 gauze-packing procedures and 523,591 cauterization procedures were recorded. Both procedures exhibited consistent seasonal patterns, peaking in winter (December to February). Age distribution followed a bimodal pattern, with higher incidence in children and older adult individuals, and a male predominance across all age groups. Pediatric patients were more likely to receive gauze packing. Geographic analysis showed a preference for gauze packing in Western Japan, whereas cauterization was more frequently performed in Northern Japan, suggesting a potential association with higher latitudes. CONCLUSION:This is the first nationwide study to identify distinct seasonal, demographic, and regional variations in epistaxis treatment in Japan. These findings suggest that factors beyond climate may influence treatment selection.

Background There is a lack of reported clinical factors associated with the outcomes of children and adolescents with avoidant/restrictive food intake disorder (ARFID) in Japan. This study aimed to identify these clinical factors and explore the relationship between ARFID and autism spectrum disorder (ASD). Methods This retrospective study analyzed data from 48 Japanese children and adolescents with ARFID who visited Okayama University Hospital between January 2011 and March 2022. Clinical characteristics were assessed using medical records and natural history questionnaires. The study compared patients with good and poor prognosis groups and used multiple logistic regression analysis to determine factors influencing prognosis. Results The study included 33 patients with good prognoses and 15 with poor prognoses. Comorbid ASD was more prevalent in the poor prognosis group (60%) compared to the good prognosis group (21%). Additionally, more than half of the ARFID patients with comorbid ASD were initially undiagnosed. Multivariate analysis revealed that older age at first visit ( p = 0.022) and comorbid ASD ( p = 0.022) were statistically significant factors associated with poor prognosis in ARFID patients. There were no significant differences in body mass index standard deviation score and maximal weight loss between the two groups. Conclusions The poor prognosis group had a higher prevalence of comorbid ASD diagnoses. Therefore, it is crucial to evaluate patient's developmental characteristics early in treatment and consider these characteristics throughout the course of care.

INTRODUCTION:Temperature control is a fundamental intervention for neuroprotection following resuscitation from cardiac arrest. However, evidence regarding the efficacy of hypothermia in post-cardiac arrest syndrome (PCAS) remains unclear. Retrospective studies suggest that the clinical effectiveness of hypothermia may depend on the severity of PCAS. The R-CAST OHCA trial aims to compare the efficacy of hypothermia versus normothermia in improving 30-day neurological outcomes in patients with moderately severe PCAS following out-of-hospital cardiac arrest. METHODS AND ANALYSIS:The multicentre, single-blind, parallel-group, superiority, randomised controlled trial (RCT) is conducted with the participation of 35 emergency and critical care centres and/or intensive care units at academic and non-academic hospitals. The study enrols moderately severe PCAS patients, defined as those with a revised post-Cardiac Arrest Syndrome for induced Therapeutic Hypothermia score of 5.5-15.5. A target number of 380 participants will be enrolled. Participants are randomised to undergo either hypothermia or normothermia within 3 hours after return of spontaneous circulation. Patients in the hypothermia group are cooled and maintained at 34°C until 28 hours post-randomisation, followed by rewarming to 37°C at a rate of 0.25°C/hour. Patients in the normothermia group are maintained at normothermia (36.5°C-37.7°C). Total periods of intervention, including the cooling, maintenance and rewarming phases, will occur 40 hours after randomisation. Other treatments for PCAS can be determined by the treating physicians. The primary outcome is a favourable neurological outcome, defined as Cerebral Performance Category 1 or 2 at 30 days after randomisation and compared using an intention-to-treat analysis. ETHICS AND DISSEMINATION:This study has been approved by the Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences and Okayama University Hospital, Ethics Committee (approval number: R2201-001). Written informed consent is obtained from all participants or their authorised surrogates. Results will be disseminated via publications and presentations. TRIAL REGISTRATION NUMBER:jRCT1062220035.

This study investigated the association between outdoor play habits during preschool and school-age obesity. We conducted a longitudinal cohort study of all children born in Japan during 2 weeks in January and July 2001. We defined outdoor play habits at age 2.5 years (third survey) as exposure, while parent-reported height and weight at age 7 years (seventh survey) were defined as overweight and obesity status using the WHO reference. Logistic regression models were used to estimate odds ratios (ORs) for associations between preschool outdoor play habits and school-age obesity, adjusting for parental and child factors. Of 53 575 children born, 42 812 had data on outdoor play habits at age 2.5 years, with 91% (38 970) having such habits. At age 7 years, 31 743/42 812 (74%) children had height and weight data, with 3249/31 743 (10%) classified as overweight or obesity (BMI SD score ≥1.0). Outdoor play habits were negatively associated with obesity (adjusted OR 0.85, 95% confidence interval (CI): 0.74–0.97). Outdoor play habits in early preschool years are associated with a reduced risk of school-age obesity. Parents and caregivers may consider encouraging their children to outdoor play habits at an early age to help prevent obesity later in life.

Minamata disease, officially identified in 1956, refers to methylmercury food poisoning that occurred in Minamata City, Japan. Although many children in the affected areas were born with severe neurological signs after birth (known as congenital Minamata disease [CMD]), little investigation has been conducted to elucidate the health effects on those who were born at the same time in the affected areas. We used historical data from a clinical study conducted in 1970 in the city of Minamata (a methylmercury-polluted area) and the island region of Amakusa (a less polluted area) to evaluate the association between prenatal methylmercury exposure and neurocognitive impairment in a total of 416 junior high school students. We divided the participants into three categories: those who lived in a highly exposed area, those who lived in a moderately exposed area (both in Minamata City), and those who lived in a less exposed area (in the Amakusa island region). We then calculated the prevalence of neurocognitive impairment in each category and estimated prevalence ratios with 95 % confidence intervals (CIs) for neurocognitive impairment compared with the less exposed area, adjusting for potential confounders. We then found that the prevalence for both neurocognitive impairment and severe neurocognitive impairment among students in the highly exposed area were 2.08 (95 % CI: 1.26 to 3.44) and 2.84 (95 % CI: 1.18 to 6.81) times higher, respectively, than those in the less exposed area. Prenatal methylmercury exposure affected neurocognitive function in CMD patients and in Minamata residents born at the same time as CMD patients in the affected areas.

BACKGROUND:The Longitudinal Survey of Newborns in the 21st Century (LSN21) tracks two Japanese national birth cohorts-2001 (baseline n = 47,010) and 2010 (n = 38,554)-from infancy through young adulthood, capturing parenting practices and family environments. Most studies analyze single exposures or outcomes. We conducted a narrative review summarizing the findings published by the Okayama University group on diverse health and developmental outcomes. METHODS:We reviewed 59 LSN21 papers (2013-2025), extracting data on exposures, outcomes, and methods. Evidence was categorized into four exposure types (infant feeding, sleep, environmental, and perinatal) and three outcome domains (obesity, allergies/respiratory tract infections, and neurobehavioral development), including cohort comparisons. RESULTS:Exclusive breastfeeding was associated with a lower obesity risk at ages 7 (adjusted odds ratio 0.55, 95% confidence interval 0.39-0.78) and 15, later puberty, and fewer hospitalizations. Short or irregular sleep before age 3 was linked to behavioral problems and injuries. Maternal smoking and prenatal air pollution were associated with respiratory conditions and developmental challenges. Preterm birth and small-for-gestational-age predicted delays, especially without catch-up growth by age 2. Pneumococcal vaccination likely contributed to declining otitis media after 2010. Additional findings included associations between outdoor play and reduced obesity risk, and complex relationships between breastfeeding and food allergies that varied by infantile eczema status. CONCLUSIONS:LSN21 findings highlight modifiable early-life factors (breastfeeding, sleep patterns, and smoke-free environments) and identify preterm and growth-restricted children for priority monitoring. While LSN21's strength lies in longitudinal social assessments, complementary perspectives from other Japanese cohorts could enhance understanding of biological mechanisms and intergenerational effects.

Background Despite Japan's universal health insurance system, health disparities have increased since the 1990s. However, the impact of area deprivation on various aspects of child health remains understudied. Methods This population-based cohort study followed 38,554 children born in Japan (May 10-24, 2010) from birth to age 5.5 years. Using an outcome-wide approach, Bayesian three-level logistic regression models (individuals in municipalities within eight major regions) assessed associations between municipality-level Area Deprivation Index (ADI) at birth and multiple preschool health outcomes (hospitalizations for all causes; respiratory infections; gastrointestinal diseases; Kawasaki disease; medical visits for asthma, allergic rhinitis, atopic dermatitis, food allergy, injury, intussusception; prevalence of overweight/obesity), adjusting for individual-level factors. Results Higher ADI was associated with increased risk of all-cause hospitalization (adjusted odds ratio [aOR] per 1-standarddeviation increase in ADI, 1.11; 95% credible interval [CI], 1.07-1.14), respiratory infections (aOR, 1.16; 95% CI, 1.11-1.21), gastrointestinal diseases (aOR, 1.19; 95% CI, 1.12-1.27), asthma (aOR, 1.06; 95% CI, 1.02-1.10), and allergic rhinitis (aOR, 1.02; 95% CI,1.00-1.04). Overweight/obesity at age 5.5 years also increased with higher ADI (aOR, 1.08; 95% CI, 1.03-1.11). Higher ADI was inversely associated with Kawasaki disease (aOR, 0.91; 95% CI, 0.83-0.998), though not robust in sensitivity analysis. Geographic clustering was observed for all outcomes, Conclusions We found persistent municipal-level health inequalities across various childhood health outcomes in Japan, despite its universal health insurance system. These findings suggest that policymakers should address health inequalities through comprehensive strategies targeting broader social determinants beyond health care access.