Defining frequent use of an urban emergency department.

Objective: This study aimed to develop a definition of frequent use of an emergency department (ED) by comparing differences in the observed frequency distribution with that of a theoretical frequency distribution.

Methods: A retrospective analysis of attendance of ED and minor injury unit attendances in one city over 1 year was conducted. From these data, the expected frequency distribution was determined based upon a Poisson distribution.

Results: During the period studied, 75,141 people attended on 98,908 occasions. The theoretical frequency distribution showed that there were 2764 (3.7%) "frequent users" presenting repeatedly due to non-random events. These patients made 12,316 (12.4%) attendances. Frequent users were older than chance users (mean age 49.7 vs 44.5 years). A greater proportion arrived by ambulance (55.3% vs 27.5%), presented with psychiatric problems (5.8% vs 1.1%) or alcohol intoxication (1.3% vs 0.5%), and were admitted to hospital (37.4% vs 19.6%).

Conclusion: We have identified that there is a group of patients who present repeatedly due to non-random events, confirming the existence of "frequent users". Their characteristics are clearly different to other patients in the ED. We propose that "frequent users" be defined as any patient who makes more than four attendances per year.