Japan Appendectomy Data Reveals Shifting Age Trends

A nationwide population-based study in Japan reveals that stable overall appendectomy rates mask significant demographic shifts, with surgical rates declining among younger populations while rising among older women. The research, published in Annals of Gastroenterological Surgery, utilized the National Database of Health Insurance Claims and Specific Health Checkups (NDB) Open Data to analyze 323,980 appendectomies performed between 2018 and 2023. This retrospective observational study provides a comprehensive overview of contemporary appendectomy epidemiology in one of the world’s most rapidly aging societies, highlighting the limitations of aggregated nationwide estimates in capturing heterogeneous temporal trends across different age and sex groups.

The study aimed to characterize nationwide temporal trends in appendectomy overall and according to age and sex, evaluate temporal changes in the operative approach from open to laparoscopic surgery, and examine associations between monthly appendectomy volume and meteorological variables. By leveraging the NDB, which accounts for more than 95% of insured medical care in Japan, the researchers were able to assess these trends at the population level with minimal selection bias. The database provides anonymized, aggregated procedure counts based on Japanese national reimbursement codes, specifically K718 for open appendectomy and K718-2 for laparoscopic appendectomy, allowing for a detailed analysis of surgical practices over the six fiscal years.

Between 2018 and 2023, the crude rate of appendectomy in Japan was 43.0 per 100,000 person-years, with an overall man-to-woman ratio of 1.30:1. Age-stratified analysis revealed a prominent peak in appendectomy rates among the young population aged 10 to 19 years, with 80.5% of all surgeries performed in patients under 65 years of age. However, while the overall age-adjusted appendectomy rate remained relatively stable, age-adjusted rates exhibited contrasting temporal patterns across different demographic subgroups. This divergence suggests that the demographic profile of patients undergoing surgery is changing substantially, even as the total number of procedures remains consistent.

Among pediatric and adolescent patients under 20 years of age, the age-adjusted appendectomy rate decreased continuously from 53.9 to 40.8 per 100,000 person-years between 2018 and 2023. In contrast, the rate among adults aged 20 to 64 years remained relatively stable, fluctuating slightly from 47.5 to 49.0 per 100,000 person-years. Conversely, the rate among older adults aged 65 years and older gradually increased from 29.0 to 31.3 per 100,000 person-years. Poisson regression models confirmed a slight but statistically significant overall decline, with a relative risk of 0.991 per year, driven primarily by a significant decrease among men, while no significant temporal change was observed among women in the overall analysis.

Sex-specific analyses further illuminated these divergent trends, showing that among men, appendectomy rates decreased significantly among those aged 5 to 39 years. Among women, rates similarly declined from 5 to 29 years of age but exhibited a plateau in the 30 to 39 age group. In middle-aged and older adults, temporal trends diverged substantially according to sex, with men showing largely stable rates from 40 to 59 years of age followed by modest increases at 60 to 74 years. Women, however, exhibited a continuous, statistically significant annual increase from 40 to 79 years of age, with particularly pronounced increases at 60 to 69 years, reaching a peak relative risk of 1.054 for women aged 60 to 64.

Concurrently, a marked and rapid transition from open to laparoscopic procedures was observed nationwide during the study period. The age-adjusted rate of open appendectomy decreased substantially from 8.68 to 2.69 per 100,000 person-years, whereas the age-adjusted rate of laparoscopic appendectomy increased from 35.07 to 40.17 per 100,000 person-years. Consequently, the proportion of laparoscopic procedures among all appendectomies increased from 80.2% in 2018 to 93.7% in 2023, establishing laparoscopic surgery as the predominant surgical approach in Japan. This shift reflects accumulated surgical experience, improvements in laparoscopic technology, and increased confidence in minimally invasive emergency surgery, representing an important change in contemporary emergency surgical practice.

The study also examined seasonal variations in appendectomy volume, finding significant seasonal variation with higher procedure numbers during summer and lower numbers during winter. Mean monthly procedure counts were highest in summer at 4,966.4 and lowest in winter at 3,887.3. Pearson correlation analyses using 30-day standardized monthly appendectomy counts demonstrated positive correlations between mean monthly temperature and appendectomy volume across five representative Japanese cities: Sapporo, Tokyo, Nagoya, Osaka, and Fukuoka. Correlation coefficients for temperature ranged from 0.837 in Sapporo to 0.845 in Nagoya, indicating a strong association between ambient temperature and surgical volume.

Time-series Poisson regression analysis further confirmed that mean monthly temperature was positively associated with monthly appendectomy volume after adjustment for calendar time and seasonal variation. The association was consistent across the five city-specific meteorological datasets, with relative risks ranging from 1.012 to 1.014 per 1°C increase in mean monthly temperature. All associations were statistically significant, with p-values ranging from 0.0027 to 0.0136. Although the underlying biological mechanisms remain unclear, proposed explanations include dehydration, alterations in gastrointestinal physiology, infectious factors, and seasonal behavioral changes. These findings should be interpreted as population-level associations due to the ecological design of the analysis.

The significant reduction in appendectomies in the younger population is likely multifactorial, potentially reflecting increasing acceptance of non-operative management for selected patients with uncomplicated appendicitis and improvements in diagnostic imaging that may have reduced unnecessary surgeries. Broader changes in environmental exposures, dietary habits, gut microbiota, and healthcare-seeking behavior may also have contributed to the observed decline. However, because patients successfully managed with non-operative management cannot be identified in the NDB Open Data, these findings should not be interpreted as evidence of a corresponding decline in the incidence of acute appendicitis. The consistent decrease observed across pediatric and adolescent age groups indicates a clear age-specific decline in appendectomy rates, but the specific drivers remain difficult to isolate from this dataset.

Conversely, the progressive increase in appendectomy rates among older women represents a distinct phenomenon that cannot be explained by population aging alone, as the analyses were based on age-specific population rates. Improvements in perioperative care, anesthetic management, and minimally invasive surgery have increased the feasibility of emergency surgery for elderly patients who may have previously been considered high-risk candidates. Advances in diagnostic imaging may also facilitate earlier diagnoses in older patients who often present with atypical clinical manifestations. The substantially greater increase observed among women suggests that additional biological, demographic, and healthcare-related factors are contributing, necessitating further investigation using patient-level clinical data to understand the mechanisms underlying this sex-specific trend.

The study had several important strengths, including the near-complete nationwide coverage provided by the NDB under Japan’s universal healthcare system, which minimizes selection bias and enables a comprehensive assessment of nationwide temporal trends. The simultaneous evaluation of demographic characteristics, operative approaches, and meteorological variables provides a broad overview of contemporary appendectomy epidemiology. Importantly, age-specific Poisson regression analyses identified substantial demographic heterogeneity that was completely masked by nationwide summary estimates, highlighting the importance of demographic stratification in population-based surgical studies. This approach allows for a more nuanced understanding of how surgical practices and disease patterns evolve across different segments of the population.

However, the study also had several limitations. The NDB Open Data comprised aggregated administrative data and excluded patient-level clinical information, such as disease severity, laboratory findings, imaging results, pathological diagnosis, and postoperative outcomes. Consequently, the data do not allow differentiation between emergency appendectomy and interval appendectomy following initial non-operative management, and appendectomies performed for uncomplicated and complicated appendicitis were analyzed together. Additionally, cases of appendicitis requiring extended resection beyond appendectomy may not have been captured if recorded under other surgical codes. The exclusion of categories containing fewer than 10 procedures may have influenced estimates in subgroups with low procedure counts, although the effect on nationwide trends is likely minimal.

Furthermore, because the study period encompassed the COVID-19 pandemic, pandemic-related changes in healthcare-seeking behavior, access to emergency care, and treatment strategies may have affected temporal trends in appendectomy rates. Although a sensitivity analysis using fiscal year as a categorical variable showed broadly consistent age-specific patterns, the potential impact of the pandemic remains a confounding factor. Finally, the ecological design of the meteorological analysis precludes causal inferences between environmental factors and the occurrence of appendectomies. The five-city analysis relied on the same nationwide monthly appendectomy counts for all locations, meaning it did not constitute independent regional replication, and the geographic consistency of the association should be interpreted with caution.

Overall, this study demonstrates that stable nationwide appendectomy rates conceal substantial age-specific demographic changes, with declining rates among younger populations and increasing rates among older women. Along with the nationwide transition toward laparoscopic surgery and consistent temperature-associated seasonal variations, these findings highlight the importance of age-stratified analyses for understanding nationwide surgical epidemiology. As Japan continues to experience rapid population aging, these demographic changes may predict future trends in the epidemiology of appendectomies in other aging countries, contributing to future healthcare planning and resource allocation for emergency surgical services.

Subject of Research: Age-specific temporal trends and climate-associated seasonality of appendectomy in Japan

Article Title: Age‐Specific Temporal Trends and Climate‐Associated Seasonality of Appendectomy in Japan: A Nationwide Population‐Based Study Using the National Database

Article References: Sumiyoshi, S., Kido, M., Arita, T., Nakamichi, N., Kurashima, K., Nanishi, K., Kiuchi, J., Shimizu, H., Yoshii, K., & Shiozaki, A. (2026). Age‐Specific Temporal Trends and Climate‐Associated Seasonality of Appendectomy in Japan: A Nationwide Population‐Based Study Using the National Database. Annals of Gastroenterological Surgery, Article ags3.70305. https://doi.org/10.1002/ags3.70305

Image Credits: AI Generated

DOI: 10.1002/ags3.70305

Keywords: appendectomy, Japan, epidemiology, laparoscopic surgery, seasonal variation, population health, surgical trends, demographic shifts, Specific, Temporal, Trends, Climate