Seasonal and cultural effects on calendar day variations in trauma incidence in Japan.

Trauma incidence patterns are influenced by societal and cultural factors. However, research has mainly focused on short-term periods. This study examined daily trauma trends throughout the year to identify fluctuations aligned with lifestyle patterns under a relatively homogeneous ethnocultural context, using long-term nationwide trauma data. Data from patients with trauma recorded in the Japan Trauma Data Bank (2004-2021; n = 383,473) were retrospectively analyzed. Participants were grouped by transport date into 365 daily cohorts. Daily patient volumes, injury severity, suicide attempts, and mortality were assessed. Outliers were identified using negative binomial regression with periodic functions, logistic regression adjusted for trauma severity, and the Generalized Extreme Studentized Deviate test. Human behavioral patterns appeared to significantly influence the trauma incidence. Cases increased during Golden Week (late April-early May), Sports Day (October 10), Culture Day (November 3), and the end of the year while declining during the Obon holiday (mid-August) and in early January. Suicide attempts peaked in May-June and September, diverging from overall trauma trends. Mortality rates remained consistent, with no significant seasonal variation or outliers. Long-term data suggest that trauma volumes vary in relation to seasonal and cultural events, offering valuable insights for optimizing trauma resource allocation and preventive strategies.