Association between emergency department crowding and mortality: a nationwide analysis stratified by emergency department levels: a retrospective cohort study

Emergency department (ED) crowding is a global health challenge associated with delayed care, compromised quality, and adverse outcomes. This study investigated the association between ED crowding and mortality, stratified by ED level. We conducted a retrospective cohort study using data from the Korean National Emergency Department Information System (NEDIS) between 2018 and 2022. Data on ED visits to Level 1 and Level 2 EDs were included, excluding those with missing data or declared dead on arrival. ED crowding was assessed using occupancy rate, the number of patients divided by available ED beds. Multivariable logistic regression identified independent predictors of in-hospital mortality, and restricted cubic spline models assessed the association between occupancy rate and mortality. Subgroup analyses were stratified by ED level. Among 25,905,347 ED visits, 433,479 in-hospital deaths occurred (1.7%). In-hospital mortality was independently associated with older age, high-acuity presentation, severe clinical conditions, abnormal vital signs. ED crowding (occupancy rate ≥ 100%) was associated with higher mortality (adjusted odds ratio aOR, 1.121; 95% CI, 1.109–1.133 in Level 1 EDs; aOR, 1.209; 95% CI, 1.180–1.238 in Level 2 EDs). Restricted cubic spline analysis showed that mortality risk increased as occupancy rates rose, with a more pronounced increase in odds observed in Level 2 EDs. This study suggests that higher ED occupancy is associated with increased in-hospital mortality, and that lower-level EDs may be particularly vulnerable to crowding-related harm. These findings highlight the potential need for dynamic crowding indicators and targeted resource support to mitigate such risks.