Background: This study aimed to evaluate the association between comorbidity and hospital admission, hospital length of stay (LOS), and in-hospital mortality among adult trauma patients across the injury severity spectrum in South Korea, and to assess whether these associations vary according to injury severity. Methods: We conducted a retrospective cohort study using the national Community-Based Severe Trauma Survey (2019–2023). Adult patients (≥18 years) with trauma were included after excluding records with missing key exposure or outcome variables. Comorbidity was defined using the ICD-10–based Elixhauser comorbidity framework. In addition to a binary classification (any vs. none), comorbidity burden was categorized into 0, 1, 2, and ≥3 conditions to evaluate dose–response relationships. The primary outcomes were hospital admission, LOS, and in-hospital mortality. Multivariable logistic regression models were used for admission and mortality, and regression models were applied for LOS, adjusting for demographic characteristics, injury mechanism, physiologic status, and system-level factors. Effect modification by injury severity was assessed using interaction terms and ISS-stratified analyses. Results: Among 49,259 patients, 32,999 (67.0%) had at least one comorbidity. Patients with comorbidities were older, had higher injury severity, and showed higher admission rates, longer LOS, and higher in-hospital mortality compared with those without comorbidities. After adjustment, comorbidity remained independently associated with increased odds of admission, prolonged LOS, and in-hospital mortality. A dose–response relationship was observed, with increasing comorbidity burden associated with progressively worse outcomes (p for trend < 0.001). In addition, substantial heterogeneity was identified across individual comorbidities, with conditions such as metastatic cancer, liver disease, coagulopathy, renal disease, and fluid and electrolyte disorders showing stronger associations with adverse outcomes. The magnitude of these associations varied across ISS strata, indicating injury severity-dependent effects. Conclusions: In this nationwide cohort, comorbidity burden and type were important determinants of acute-care utilization and in-hospital mortality among trauma patients. Incorporating comorbidity information into early risk stratification may improve prognostic accuracy and support more efficient resource allocation and clinical decision-making across the trauma care continuum.

Background/Objectives: Injury mechanism and intent are key determinants of patient outcomes in the emergency department, yet their combined effects remain insufficiently understood. Emergency department disposition after injury may differ according to mechanism and intent and may be further influenced by specific mechanism–intent combinations. This study aimed to evaluate the associations of injury mechanism, intent, and their interaction with emergency department disposition and injury severity measured using the International Classification of Diseases-based Injury Severity Score (ICISS). Methods: We conducted a retrospective analysis of injury-related emergency department visits recorded between 1 January 2019 and 31 December 2023. Eligible visits included those with valid arrival and departure timestamps and complete disposition data; records with missing key variables or implausible length of stay were excluded. A total of 1,029,875 visits were analyzed. The primary outcome was emergency department disposition, categorized as discharge, admission, or transfer. Multinomial logistic regression was used to estimate relative risk ratios, with discharge as the reference category, and to derive predicted probabilities for selected mechanism–intent combinations. Injury severity was assessed using ICISS and modeled with injury mechanism, intent, their interaction, and prespecified covariates. Results: Of all visits, 69.9% resulted in discharge, 24.3% in admission, and 5.8% in transfer. Compared with traffic accidents, the highest likelihood of admission was observed in suffocation, drowning, and poisoning injuries. Transfer was more frequent in drowning, suffocation, penetrating injuries, and poisoning. Self-harm was associated with increased risks of both admission and transfer compared with unintentional injuries. Interaction analyses showed that certain combinations, particularly poisoning with self-harm and suffocation with self-harm, were associated with substantially higher risks than either factor alone. Predicted probabilities further highlighted high-risk combinations, including markedly elevated admission probabilities in self-harm-related poisoning and suffocation, and increased transfer probability in unintentional drowning. Injury mechanism, intent, and selected interactions were also significantly associated with ICISS-based injury severity. Conclusions: Injury mechanism and intent are independently associated with emergency department disposition and injury severity, with additional risk amplification observed for specific combinations. These findings suggest that mechanism–intent combinations may serve as clinically useful risk indicators in emergency department triage and decision-making, supporting improved risk stratification and system-level coordination.