A population-based study of the burden of severe asthma in Alberta, Canada

Figures & data

Figure 1. Study flow chart.

Table 1. Descriptive statistics for the severe asthma cohort by disease control at index date; Alberta, Canada.

Characteristic	Overall (n, %)	Controlled (n, %)ª	Uncontrolled (n, %)ª
Total
Number of patients	74,134 (100.0)	71,099 (95.9)	3,035 (4.1)
Age (years)^b,c
Mean (SD)	47.0 (19.6)	47.2 (19.6)	42.8 (19.2)
Median (IQR)	47.0 (32.0-62.0)	48.0 (32.0-62.0)	43.0 (27.0 − 57.0)
Age (years)^b,c
12-17	5,910 (8.0)	5,534 (7.8)	376 (12.4)
18-49	33,763 (45.5)	32,270 (45.4)	1,493 (49.2)
50-64	19,167 (25.9)	18,421 (25.9)	746 (24.5)
65-79	11,471 (15.5)	11,122 (15.6)	349 (11.5)
> = 80	3,823 (5.2)	3,752 (5.3)	71 (2.3)
Sex
Female	42,977 (58.0)	41,118 (57.8)	18,59 (61.3)
Male	31,157 (42.0)	29,981 (42.2)	1,176 (38.8)
Health zone at index date
Rural	21,343 (28.8)	20,200 (28.4)	1,143 (37.7)
Urban	52,791 (71.2)	50,899 (71.6)	1,892 (62.3)
Charlson comorbidity index score^d
0	15,566 (21.0)	15,566 (21.9)	0 (0.0)
1 to 3	55,887 (75.4)	52,933 (74.5)	2,954 (97.3)
3+	2,420 (3.3)	2,339 (3.3)	81 (2.7)
No health care visit within the defined time window for CCI index	261 (0.4)	261 (0.4)	0 (0.0)
Comorbid COPD at index
No	67,789 (91.4)	65,210 (91.7)	2,579 (85.0)
Yes	6,345 (8.6)	5,889 (8.3)	456 (15.0)
Chronic oral corticosteroids within 12 months before index date
No	69,686 (94.0)	66,757 (93.9)	2,929 (96.5)
Yes	4,448 (6.0)	4,342 (6.1)	106 (3.5)

Abbreviations: CCI, Charlson Comorbidity Index; COPD, chronic obstructive pulmonary disease IQR, interquartile range N/A, not applicable; SD, standard deviation.

^aAsthma control status as of index date. Values represent the number and percent of patients unless otherwise indicated.

^bAge at index date.

^cAge and sex were derived from the Population Registry.

^dThe Charlson Comorbidity Index Score was derived from the Discharge Abstract Database, National Ambulatory Care Reporting System, and Practitioner Claims, 1 year prior to or including the index date.

Figure 2. Treatment patterns among individuals age 12+ years identified as having severe asthma in Alberta, Canada; fiscal years 2011–2019. The first four lines of therapy were assessed from 1-year pre-index. The height of each bar represents the proportion of patients on each line of therapy. Curves represent the proportion of patients transitioning from one line of therapy to the next. Treatment combinations are defined in Online Supplementary Material 3. Abbreviations: LTRA, leukotriene receptor antagonist; OCS, oral corticosteroid.

Table 2. Asthma exacerbation episodes^a during follow-up by disease control; Alberta, Canada, fiscal years 2012-2019.

	Overall^b	Controlled^c	Uncontrolled^c
Total
Number of exacerbations^a	47,824	37,165	10,659
Mean (SD) annualized ERPP	0.113 (0.33)	0.092 (0.24)	0.602 (1.01)
Mean (SD) exacerbation episode duration in days	6.7 (5.7)	6.6 (5.4)	6.6 (5.0)
Median (IQR) exacerbation episode duration in days	5 (4-8)	5 (4-8)	5 (3-9)
IRR (95% CI); p-value	N/A	Ref	5.5 (5.1-5.8); p < .0001
Hospitalizations
Number of exacerbations^a	1,952	1,146	806
Mean (SD) annualized hospitalization ERPP	0.005 (0.052)	0.003 (0.031)	0.046 (0.201)
Mean (SD) exacerbation episode duration in days	10.3 (9.6)	10.2 (9.0)	10.5 (10.5)
Median (IQR) exacerbation episode duration in days	7 (5-13)	7 (5-12)	7 (5 − 13)
IRR (95% CI); p-value	N/A	Ref	13.2 (11.1-15.8); p < .0001
ED visits
Number of exacerbations^a	17,461	12,741	4,720
Mean (SD) annualized ED visit ERPP	0.041 (0.193)	0.031 (0.123)	0.273 (0.709)
Mean (SD) exacerbation episode duration in days	4.1 (4.5)	4.0 (4.2)	4.5 (5.1)
Median (IQR) exacerbation episode duration in days	2 (1-5)	2 (1-5)	3 (1-6)
IRR (95% CI); p-value	N/A	Ref	6.6 (6.1-7.2); p < .0001
OCS bursts
Number of exacerbations^a	28,411	23,278	5,133
Mean (SD) annualized OCS burst ERPP	0.067 (0.206)	0.058 (0.175)	0.284 (0.516)
Mean (SD) exacerbation episode duration in days	8.0 (5.4)	7.8 (5.2)	8.9 (6.1)
Median (IQR) exacerbation episode duration in days	6 (5-10)	6 (5-9)	7 (5-10)
IRR (95% CI); p-value	N/A	Ref	4.4 (4.1-4.7); p < .0001

Abbreviations: CI, confidence interval; ED, emergency department, ERPP, exacerbation rate per person; IRR, incidence rate ratio; IQR, interquartile range, N/A, not applicable, OCS, oral corticosteroids, Ref, referent group, SD, standard deviation.

^aExacerbations occurring within 48 h of each other were combined into a single exacerbation episode. As such, episode durations may include multiple exacerbation events.

^bOverall: controlled and uncontrolled, combined.

^cAsthma control status as of index date; data represents asthma control status indexed prior to March 31, 2019.

Table 3. Asthma-specific HCRU by disease control^a,b pre-index and during follow-up; Alberta, Canada, fiscal years 2008-2019.

	3 years pre-index			Follow-up
	Overall^c	Controlled	Uncontrolled	Overall	Controlled	Uncontrolled
Total
Number of patients	72,147	69,262	2,885	72,147	69,262	2,885
Hospitalizations
Annualized rate, mean (SD)	0.0 (0.1)	0.0 (0.0)^d	0.1 (0.3)	0.0 (0.1)	0.0 (0.0)^d	0.1 (0.2)
Patients with at least 1 hospitalization, n (%)	1,179 (1.6)	385 (0.6)	794 (27.5)	1,158 (1.6)	816 (1.2)	342 (11.9)
Length of stay (days), mean (SD)^e	4.0 (3.4)	3.9 (3.9)	3.98 (3.2)	4.21 (3.9)	4.25 (4.2)	4.13 (3.2)
Length of stay (days), median (IQR)^e,f	3.0 (2.0-5.0)	3.0 (2.0 − 5.0)	3.0 (2.0-5.0)	3.0 (2.0-5.0)	3.0 (2.0-5.0)	3.0 (2.0-5.0)
ED admissions
Annualized admission rate, mean (SD)	0.1 (0.3)	0.1 (0.2)	0.8 (1.0)	0.1 (0.3)	0.0 (0.2)	0.4 (0.9)
Patients with at least 1 ED admission, n (%)	9,510 (13.2)	7,343 (10.6)	2,167 (75.1)	9,031 (12.5)	7,688 (11.1)	1,343 (46.6)
Length of stay (hours), mean (SD)^e	3.5 (3.1)	3.3 (3.1)	4.0 (3.2)	3.4 (2.7)	3.4 (2.7)	3.7 (2.9)
Length of stay (hours), median (IQR)^e,f	2.6 (1.5-4.4)	2.5 (1.4-4.2)	3.2 (1.9-5.1)	2.8 (1.6-4.4)	2.7 (1.6-4.4)	3.1 (1.9-5.0)
GP visits
Annualized visit rate, mean (SD)	0.7 (1.0)	0.6 (0.9)	2.2 (2.2)	0.6 (1.1)	0.6 (1.0)	1.5 (2.0)
Annualized visit rate, median (IQR)^f	0.3 (0.0-1.0)	0.3 (0.0-0.7)	1.7 (1.0-2.7)	0.3 (0.0-0.8)	0.3 (0.0-0.8)	0.9 (0.4-2.0)
Specialist visits
Annualized visit rate, mean (SD)	0.3 (0.9)	0.2 (0.7)	1.4 (2.5)	0.3 (0.9)	0.2 (0.7)	1.3 (2.9)
Spirometry tests
Annualized visit rate, mean (SD)	0.0 (0.1)	0.0 (0.1)	0.0 (0.1)	0.0 (0.0)	0.0 (0.0)	0.0 (0.1)
Medication dispenses
Annualized dispense rate, mean (SD)	5.8 (7.5)	5.6 (7.2)	10.5 (12.4)	7.8 (9.9)	7.6 (9.2)	14.4 (19.1)

Abbreviations: ED, emergency department; GP, general practitioner; HCRU, healthcare resource utilization; LOS, length of stay; n, sample size; Q, quartile; SD, standard deviation.

^aAsthma control status as of index date.

^bHCRU cohort required at least 1 year of follow up.

^cOverall refers to controlled and uncontrolled, combined.

^dMean (SD) annualized hospitalization rates among controlled patients were zero in the pre-index due to the applied definition of being controlled; rate did not change over follow-up.

^eLength of stay was calculated only for patients who had at least 1 admission.

^fFor outcomes with skewed data, both the mean (SD) and median (IQR) are presented. Medians were not included when the data did not have a skew.

Figure 3. Annual mean healthcare costs associated with severe asthma in individuals age 12+ years in Alberta, Canada; fiscal years 2012–2019. Costs are per patient in Canadian dollars relative to patient index dates when severe asthma was identified. Some values are not shown; specifically, the pre-index annual mean costs of ED admission and inpatient hospitalizations, respectively, were $35.00 and $44.00 overall and $21.00 and $13.00 in the controlled cohort. The post-index annual mean costs of ED admission and inpatient hospitalizations cost, respectively, were $23.00 and $32.00 overall, and $17.00 and $19.00 in the controlled cohort. Abbreviations: ED, emergency department.