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Flu outbreaks account for nearly 25% of ED overcrowding


Flu patients in emergency departments (EDs) during flu season account for nearly a quarter of ED overcrowding during that period, a new study from the Institute for Clinical Evaluative Sciences (ICES) shows.

To study the specific effect that flu outbreaks have on ED overcrowding, researchers obtained weekly data on laboratory-confirmed flu and other respiratory virus cases, ED overcrowding (measured as the average number of hours per week where EDs were forced to divert all ambulances), and visits to the 21 acute care hospital EDs in the city of Toronto between January 1996 and April 1999. Flu season typically occurs between November and March.


  • Overall, EDs experienced an average of 3.4 hours per week of overcrowding during the study period.
  • During flu season, for every 100 flu cases that occurred in the community, there were an extra 2.5 hours per week of overcrowding in EDs, on average.
  • On average, EDs experienced a total of 344 hours of overcrowding over all four flu seasons in the study period, of which 83 hours were attributable to the flu. This represents 24.3% of the duration of ED overcrowding during the flu seasons.

“Our results confirm what many in the healthcare community have long suspected – that flu outbreaks significantly impact ED overcrowding,” said lead author and ICES scientist Dr. Michael Schull. “But even we were surprised by just how big the effect is.”

“It’s important to note that the impact of flu season on EDs is not because of an increase in the number of young patients visiting EDs with mild flu symptoms. Rather, we think it’s mainly because of a smaller number of patients, particularly the elderly, who are sick with complications of the flu and are more likely to require hospitalization. Hospitals then have trouble coping with the extra burden.

“Measures that could lessen the impact of flu outbreaks on patients and EDs include increasing community-wide rates of flu vaccination, improving access to inpatient beds during outbreaks, and enhancing alternatives to EDs for the medical care of patients suffering influenza complications, particularly the elderly,” said Dr. Schull.

However, Dr. Schull stresses, “the most important message of this study is that every flu case that’s prevented helps reduce the strain on our hospitals. Each of us can do our part to protect ourselves, our family, and the healthcare system by getting the free flu shot.”

The study, “Community influenza outbreaks and emergency department ambulance diversion”, appeared in the July 2004 issue of the Annals of Emergency Medicine.

Author affiliations: ICES (All authors); Clinical Epidemiology Unit, Department of Medicine, University of Toronto (Dr. Schull); Department of Emergency Services, Sunnybrook and Women’s College Health Sciences Centre, University of Toronto (Dr. Schull).

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.


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