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The Ontario Asthma Regional Variation Study: emergency department visit rates and the relation to hospitalization rates.

BACKGROUND
Hospitalization rates for asthma vary more than threefold across regions of Ontario. It is not known whether this variation is primarily due to regional differences in the rate of emergency department (ED) visits or hospital admissions.


OBJECTIVE
To determine the variation in ED visit rates for asthma in Ontario, and the relation between ED visit rates and hospitalization rates.


DESIGN, SETTING, AND PATIENTS
We studied patients with an ED disposition diagnosis of asthma in a stratified sample of 16 hospitals (pediatric facilities, 13; adult facilities, 14) over a 1-year period. Pediatric patients were defined as those patients who were </= 19 years of age.


MEASUREMENTS
Direct age-standardized and sex-standardized ED visit and hospitalization rates, and the percentages of patients presenting to EDs and subsequently admitted to the hospital were calculated for each site. High/low ratios (ie, extremal quotients [EQ]), weighted coefficients of variation (CVs), and the systematic component of variation (SCV) were used to summarize the variation among hospitals.


RESULTS
The total number of ED visits for asthma at participating sites was 12,518 (7,825 children and 4,693 adults). A total of 847 children (10.8%) and 322 adults (6.9%) were admitted to the hospital. Age-standardized and sex-standardized ED visit rates ranged from 8.7 to 25.2 per 1,000 population for children (EQ, 2.9; CV, 30.9%; SCV, 173; p < 0.001) and 1.7 to 10.1 per 1,000 population for adults (EQ, 5.9; CV, 52.9; SCV, 445; p < 0.001). The proportion of pediatric and adult ED visits resulting in admission to the hospital varied significantly by site (p < 0.001) and was inversely related to ED visit rates in children (p < 0.001) but not in adults. ED visit rates were related to hospitalization rates in children (p = 0.042) and adults (p < 0.0001), but only accounted for 4% and 27%, respectively, of the variation in hospitalization rates.


CONCLUSION
Hospitalization rates for asthma in Ontario are primarily influenced by the variation in the percentage of ED visitors admitted to the hospital rather than the ED visit rate.