Rationale: Severe sepsis is common and highly morbid, yet the epidemiology of severe sepsis at the frontier of the health care systempre-hospital emergency care-is unknown. Objectives: We examined the epidemiology of pre-hospital severe sepsis among emergency medical services (EMS) encounters, relative to acute myocardial infarction and stroke. Methods: Retrospective study using a community-based cohort of all nonarrest, nontrauma King County EMS encounters from 2000 to 2009 who were transported to a hospital. Measurements and Main Results: Overall incidence rate of hospitalization with severe sepsis among EMS encounters, as well as pre-hospital characteristics, admission diagnosis, and outcomes. Among 407,176 EMS encounters, we identified 13,249 hospitalizations for severe sepsis, of whom 2,596 died in the hospital (19.6%). The crude incidence rate of severe sepsis was 3.3 per 100 EMS encounters, greater than for acute myocardial infarction or stroke (2.3 per 100 and 2.2 per 100 EMS encounters, respectively). More than 40% of all severe sepsis hospitalizations arrived at the emergency department after EMS transport, and 80% of cases were diagnosed on admission. Pre-hospital care intervals, on average, exceeded 45 minutes for those hospitalized with severe sepsis. One-half or fewer of patients with severe sepsis were transported by paramedics (n ¼ 7,114; 54%) or received pre-hospital intravenous access (n ¼ 4,842; 37%). Conclusions: EMS personnel care for a substantial and increasing number of patients with severe sepsis, and spend considerable time on scene and during transport. Given the emphasis on rapid diagnosis and intervention for sepsis, the pre-hospital interval may represent an important opportunity for recognition and care of sepsis.Keywords: sepsis; emergency medical services; epidemiology Severe sepsis represents a large and increasing burden on the U.S. health care system. The incidence of severe sepsis is greater than 3.0 per 1,000 population, and case fatalities approach 20%, accounting for more than $17 billion annually in medical costs (1-3). Even sepsis survivors often suffer with cognitive impairment and functional disability (4, 5). Advances in severe sepsis therapy, such as time-sensitive antibiotic administration and fluid resuscitation, require prompt diagnosis, and in some cases, transfer to referral centers for definitive therapy (6-11). Until now, such early recognition occurs after patients arrive at hospitals, when a critical window for treatment and referral may already have passed.An alternative approach may be to diagnose and treat severe sepsis in the pre-hospital period, using emergency medical services (EMS) personnel (12, 13). More than 800,000 EMS personnel provide care to tens of millions of persons as part of an emergency system (14) that transports more than 35 patients every minute of every day (15). EMS systems already play a key role in the management of acute cardiovascular disease, stroke, and trauma, conditions that benefit from care at optimal centers with advanced ...