Community influenza outbreaks and emergency department ambulance diversion☆
Received 16 April 2003; received in revised form 24 September 2003, 4 November 2003 and 24 November 2003; accepted 10 December 2003.
Abstract
Study objective
Influenza has been linked to emergency department (ED) crowding, yet few studies have examined this association. We describe the relationship between ED crowding and influenza outbreaks.
Methods
A retrospective time series analysis was conducted in Toronto from January 1996 to April 1999 (n=170 weeks). We obtained weekly data on laboratory-confirmed influenza and other respiratory virus cases in the community, ED ambulance diversion, and visits to all city EDs (n=20). The main outcome was ambulance diversion, measured as the mean number of hours per week in which EDs were forced to divert all ambulances.
Results
A mean of 10,936 ED visits occurred weekly (average age of patients 39.9 years; 51% female patients). EDs diverted ambulances an average of 3.4 hours per week (range 0.3 to 15 hours). Four influenza seasons occurred, lasting between 18 and 30 weeks each, with weekly influenza case counts ranging from 0 to 236. There were fewer than 10 cases per week in 119 of 170 weeks (70%). In time-series models, influenza was independently associated with ED ambulance diversion (P<.0001). For every 100 cases of influenza in the community in a given week, ED ambulance diversion would be expected to increase by 2.5 h/wk at the average ED (95% confidence interval [CI] 1.2 to 3.9 h/wk). During influenza seasons, 24.3% (95% CI 11.3% to 37.2%) of observed weekly ambulance diversion was attributable to influenza.
Conclusion
Influenza seasons are associated with increased ED ambulance diversion. The impact is substantial but brief because there is little or no influenza activity most of each year.
From the Institute for Clinical Evaluative Sciences (Schull, Mamdani, Fang); the Clinical Epidemiology Unit, Department of Medicine, University of Toronto (Schull); and the Department of Emergency Services, Sunnybrook and Women's College Health Sciences Centre, University of Toronto (Schull), Toronto, Ontario, Canada
Address for correspondence: Michael J. Schull, MD, MSc, G-147, Sunnybrook and Women's College Health Sciences Centre, 2075 Bayview Avenue, Toronto, Ontario, Canada, M4N 3M5; 416-480-6100 ext. 3793, fax 416-480-6048
☆ Author contributions: MJS originated the hypothesis, designed the study, and had main responsibility for interpreting the results and writing the manuscript. MMM helped design the study, conducted multivariate data analyses, helped interpret the results, and helped write the manuscript. JF established the databases necessary for the study and helped with data analysis and manuscript editing. MJS takes responsibility for the paper as a whole.
Supported by a grant from the Peter Lougheed Medical Research Foundation, as well as by Career Awards for both Dr. Schull and Dr. Mamdani from The Canadian Institutes for Health Research.
ABSTRACT