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

This study investigated nationwide temporal trends, age-specific changes, and seasonal variations in appendectomies in Japan using the national database of health insurance claims and specific health checkups (NDB).

Data on appendectomies (open [OA] and laparoscopic [LA]) were extracted from the 2018-2023 NDB Open Data. Crude and age-adjusted appendectomy rates per 100,000 person-years were calculated. Temporal trends were assessed using Poisson regression, and age-specific annual relative risks were estimated. Seasonality (April 2019 to March 2024) was evaluated, and correlations with meteorological variables were assessed using Pearson correlation coefficients. Time-series Poisson regression was used to evaluate the association between monthly appendectomy volume and ambient temperature.

During the study period, 323,980 appendectomies were performed. The age-adjusted appendectomy rate declined slightly overall (relative risk [RR] = 0.991, p < 0.0001), with a significant decrease in men (RR = 0.982, p < 0.0001), whereas no significant change was observed in women (RR = 1.003, p = 0.0676). Age-specific analyses demonstrated declining appendectomy rates among younger populations, whereas the overall rates increased after approximately 40 years of age, with larger increases observed among women than men. OA use decreased (RR = 0.793, p < 0.0001), whereas LA use increased (RR = 1.022, p < 0.0001). The monthly appendectomy volume exhibited significant seasonality and was positively correlated with ambient temperature using meteorological data from five cities.

Appendectomy rates decreased in younger populations but increased among older adults, particularly women. A shift toward laparoscopic surgery and temperature-associated seasonality was also observed.