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Acad Emerg Med. 2014 Oct;21(10):1092-100. doi: 10.1111/acem.12480.

Increases in emergency department occupancy are associated with adverse 30-day outcomes.

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The Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montréal, Québec; St. Mary's Research Centre, Montréal, Québec.

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The associations between emergency department (ED) crowding and patient outcomes have not been investigated comprehensively in different types of ED. The study objective was to examine the associations of changes over time in ED occupancy with patient outcomes in a sample of EDs that vary by size and location. A secondary objective was to explore whether the relationship between ED occupancy and patient outcomes differed by ED characteristics (size/type and medical and nursing staffing ratios).


Using linked administrative databases, the authors constructed a cohort of 677,475 patients who visited one of 42 hospital EDs with complete data for 2005 on ED bed and waiting room occupancy. Crowding was measured with the relative occupancy ratio separately for ED bed and waiting room patients, defined as the ratio of ED occupancy on the day of the index ED visit to the average annual occupancy at that same ED. Multivariable logistic regression (adjusting for patient and ED characteristics) was used to analyze 30-day outcomes: mortality, return ED visits, and hospital admission at the first return ED visit.


After adjustment for ED and patient characteristics, a 10% increase in ED bed relative occupancy ratio was associated with 3% increases in death and hospital admission at a return visit. A 10% increase in ED waiting room crowding was associated with a small decrease in return visits. There was a stronger association between bed crowding and mortality among larger EDs.


In Quebec EDs, increases in bed occupancy are associated with an increase in the rates of 30-day adverse outcomes, even after adjustment for patient and ED characteristics. The results raise important concerns about the quality of care during periods of ED crowding.

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