A national description of emergency medical services patient utilization patterns.

Introduction: Repeat use of 9-1-1 emergency medical services (EMS) reflects complex intersections of medical need, social vulnerability, and health system failures. While high utilization of emergency departments has been extensively studied, national characterizations of EMS utilization patterns remain limited. Methods: We conducted a retrospective analysis of 9 508 809 EMS encounters involving 6 604 938 unique patients using the 2024 ESO Data Collaborative. A novel patient-level linkage approach using the Levenshtein distance method identified repeat encounters across time. EMS utilization was categorized as low (1), moderate (2-4), high (5-11), and very-high (12+ encounters). Results: Three percent of patients accounted for 16% of all encounters. Patients with very-high utilization were disproportionately covered by Medicaid, resided in socioeconomically vulnerable communities, and more commonly presented with chronic conditions. Despite higher transport rates, they were 40% less likely to be admitted than single-encounter patients. The median time between encounters was 10 days for very-high utilizers. Conclusion: These patterns are consistent with broad health and healthcare access challenges rather than individual patient behavior. EMS utilization data may offer a means to identify high-need, low-access populations and develop strategies that improve care coordination and reduce emergency system strain.