Rate and Cost of Hospitalizations for Asthma in Quebec: An Analysis of 1988/89, 1989/90 and 1994/95 Data

Claudine Laurier, Wendy Kennedy, Jean-Luc Malo, Michèle Paré, Daniel Labbé, André Archambault and André-Pierre Contandriopoulos

Introduction

Asthma is a common disease of both adults and children, causing breathing impairment with consequences dependent on the severity of the disorder. Studies have estimated the population prevalence as 3%¹ and 7%² in the adult population and over 10% in children.³ According to the 1987 Santé Québec survey, the prevalence of asthma, bronchitis and emphysema (as one comprehensive category) was 3.9% in the general Quebec population.⁴ Santé Québec has published the prevalence by sex (4.1% among women and 3.9% among men) and by age group for some groups: 4.1% among those aged less than 15 years, 3.2% among those 15S24, 4.4% among those 45S64 and 7.1% among those 65 and older.⁴

Rates of Quebec hospitalizations for asthma increased during the decade from the early 1970s to the early 1980s, by 79% to 1.56 per 1000 among males and by 58% to 1.33 per 1000 among females.⁵ The early 1980s may have seen a decrease: in 1984/85 there were 9080 hospitalizations for asthma in Quebec, down from 11,726 in 1980/81.⁶ Over the entire 1980s there was an average increase in the annual rate of hospitalizations of 3.3%.⁷ In Canada, the number of hospitalizations increased at an average rate of 1.8% per year from 1981 to 1989, and the mean length of stay decreased from 6 to 4.7 days over the same period.⁸ Hospitalization rates differed across age groups—in 1988 the estimated rate was 5.82 per 1000 among those under 15 years old and 0.66 among those aged 15 to 34.⁸ Asthma hospitalization was subject to a substantial seasonal influence, the rate peaking in autumn.^9,10

The preceding data describe the situation in the 1980s. With the increase in use of inhaled corticosteroids (from 6 per 1000 Saskatchewan inhabitants in 1989 to 20 per 1000 in 1993¹¹), reflecting the dissemination of guidelines and recommendations for treatment of asthma, there could be a decrease in the need for hospitalization due to asthma. Such a decrease was seen recently in Sweden.¹² Offsetting this expected trend is the increase in the prevalence of asthma that is generally agreed to be taking place.¹³

Inasmuch as the cost of asthma treatment is important, relatively up-to-date estimates of the cost of hospitalization for asthma—a major component of overall costs—are of interest. The direct costs of asthma in Canada for 1990 were estimated to be $306 million; hospital in-patient care was an estimated $84.4 million, excluding drugs.¹⁴

To explore the hypothesized changes in rates of hospitalization and to estimate the cost of this area of asthma treatment, we examined rates of hospitalization with a primary diagnosis of asthma for the Quebec population during three one-year periods: 1988/89, 1989/90 and 1994/95. Rates and average lengths of stay of such hospitalizations were established, and those for 1994/95 were examined according to age, sex and month of admission. The costs associated with the 1994/95 asthma hospitalizations were then estimated.

Methods

This study used the MED-ECHO database for fiscal years 1988/89, 1989/90 and 1994/95 (i.e. from April 1 until March 31 for each year). MED-ECHO is an electronic database that contains detailed hospitalization summaries. The database includes information on the principal diagnosis and up to 16 associated diagnoses, dates of admission and separation, length of stay, ward, major procedures undergone as well as the age and sex of the patient. All hospitalizations with the principal diagnosis of asthma (ICD-9 codes 493.0 to 493.9) were retrieved for the relevant years. As MED-ECHO annual files are organized according to date of separation, the hospitalizations analyzed in this study included those in which the patient was admitted during the previous period but discharged in the period of study. On the other hand, hospitalizations for patients admitted during the period of study but discharged in the subsequent period were not included. Less than 1% of retrieved hospitalizations were in long-stay hospitals or were for a period of greater than 30 days. These long-stay hospitalizations were excluded from the analysis, as they were likely to be related to conditions other than simple asthma.

Population data represented the population eligible for the Health Insurance Program on July 1st of the respective year (1989, 1990 and 1995) and was lower by about 86,000 than the total estimated population of roughly 7 million.¹⁵ It should be noted that MED-ECHO reports the number of hospitalizations and not the number of people hospitalized in any given period. The rates presented here must be interpreted accordingly.

Rate of hospitalization per 1000 and length of stay were estimated by age group and sex for the three one-year periods. Age (in years) was grouped as follows: less than 1, 1S4, 5S9, 10S14, 15S19, 20S39, 40S64, 65S74, and 75 and older. The 1994/95 hospitalization rates were also analyzed by month of admission. Differences in the average length of stay among patients according to the month of admission, age group and sex were tested for significance using parametric or non-parametric tests (t-test, analysis of variance [ANOVA] or Kruskall-Wallis). A two-way ANOVA was performed for age and sex.

The cost of asthma hospitalization was estimated by means of two methods. The first used the 1994/95 financial data for all short-stay hospitals (excluding psychiatric hospitals). A per diem specific to the hospital ward was calculated, which included nursing care, pharmacy, laboratory, “hotel,” administration and maintenance costs; it excluded capital cost investment and physician reimbursement. The recorded length of stay was multiplied by the per diem.

The second approach used an index reflecting the relative use of resources (NIRRU) for each hospitalization classified according to its All-Patient Refined Diagnostic-Related Group (APR-DRG).¹⁶ These APR-DRGs constitute 1530 groups of clinically homogeneous patients requiring an equivalent level of resources. They are based on diagnosis, severity and probability of poor outcome. Among other changes to the previous versions of the DRG classifications, the APR-DRG system has incorporated certain specific pediatric DRGs. For each APR-DRG, a NIRRU was created.

The NIRRU was based on costs per APR-DRG for typical patients established in Maryland in 1994. The cost for each APR-DRG was divided by the mean cost for all hospitalizations to obtain a relative weight, where 1.00 corresponded to the mean. This index was then adjusted to take into account the differences in lengths of stay between Maryland and Quebec (see Appendix). A NIRRU was calculated for each asthma hospitalization and was applied to the average cost of hospitalizations in the province of Quebec for 1994 to establish a cost per asthma hospitalization.

Total and average costs for all asthma hospitalizations were estimated using both methods, and 95% confidence intervals were calculated for average costs per NIRRU-adjusted asthma hospitalization.

Results

Hospitalization Rates for Asthma

From 1989 to 1995, the population of Quebec eligible for health benefits increased by 4.1%, from 6.91 million to 7.19 million. The rate of the total number of hospitalizations less than 30 days (for any reason) at the end of that period was 14.8% higher than at the beginning, increasing from 142 per 1000 in 1988/89 to 163 per 1000 in 1994/95. The proportion of Quebec hospitalizations associated with asthma as the principal diagnosis was 1.1% in 1994/95, slightly lower than in 1988/89 (1.2%). The rate of hospitalization with asthma as the principal diagnosis was 1.76 per 1000 in 1988/89, fell to 1.44 in 1989/90 and rose to 1.75 in 1994/95 (Table 1).

Rates were estimated at 1.85 per 1000 among men and 1.67 per 1000 among women in 1988/89, falling to 1.79 and 1.71 per 1000, respectively, in 1994/95 (Table 1).

The hospitalization rate for children less than 1 year old in 1994/95 was twice as high as in 1988/89 or 1989/90. In the 1S4 age group, it remained relatively the same but slightly lower than the 1988/89 figure.

Figure 1 shows that hospitalization rates for asthma in 1994/95 were highest among male infants under the age of 1 year, and high among boys aged 1S4. As well, boys under 5 were hospitalized at a rate roughly twice that of their female counterparts. In the age groups of 10 years and older, however, the rates among women were higher, and females aged 20S39 were hospitalized at roughly twice the rate of their male counterparts.

TABLE 2 Quebec hospitalizations with asthma as principal diagnosis (LOS <=30 days) and mean length of stay (LOS), by age and sex, 1994/95
Age group	Hospital separations: MALES			Hospital separations: FEMALES
	n	Mean LOS (days)	LOS 95% CI	n	Mean LOS (days)	LOS 95% CI
<1	783	3.57	3.38–3.74	338	3.49	3.21–3.77
1–4	2,824	2.40	2.33–2.47	1,491	2.36	2.28–2.44
5–9	766	2.23	2.13–2.33	575	2.46	2.34–2.58
10–14	410	2.55	2.39–2.71	449	3.09	2.88–3.29
15–19	188	2.72	2.43–3.01	394	3.10	2.83–3.37
20–39	443	3.88	3.59–4.16	867	4.08	3.85–4.31
40–64	495	5.10	4.73–5.47	1,215	5.97	5.71–6.24
65–74	239	6.83	6.13–7.54	500	7.62	7.13–8.10
75+	186	7.94	7.05–8.82	440	8.48	7.93–9.02
TOTAL	6,335	3.19	3.12–3.26	6,269	4.31	4.21–4.41

Cost of Hospitalizations for Asthma

The results of the cost estimation for asthma hospitalizations in Quebec for the year 1994/95 are presented in Table 3. For the first method of calculation, using the per diem for short-stay hospitals ($379),¹⁷ the average 1994/95 cost per stay was approximately $1400 and the total cost was $17.9 million.

A NIRRU was estimated for all 1994/95 short-stay asthma hospitalizations except 54 (0.4%). The average NIRRU for all the asthma hospitalizations was 0.6 (±0.003), and this varied according to the ward in which the patient was treated (Table 3). The average cost per stay was $1676 (95% CI = 1661S1692). Of the total cost of $21.0 million, the greatest proportion was accounted for by the Pediatrics ward ($9.9 million). The NIRRU-adjusted cost per stay was lowest in Allergy ($1397) and Pediatrics ($1,413) wards, where the average lengths of stay were shortest, and highest in Internal Medicine ($2150) and Other ($2348) wards, where the average lengths of stay were highest.

Discussion

Earlier studies found an increase in the hospitalization rate for asthma in Quebec from the early 1970s to the early 1980s.⁵ The hospitalization increases during that period for all of Canada were greatest in persons under the age of 15.⁵ From 1981 to 1988, the overall Canadian age-standardized rate of hospitalizations rose by roughly 40%. Although the rate in Quebec was lower than the national average, the increase was relatively high, at 70% and 77% for those under 15 and ages 15-35, respectively.⁸

Our data show that asthma hospitalization rates were lower in 1989/90 than in 1988/89. As well, mean length of stay was shorter in 1989/90 than in 1988/89. In 1994/95, a return to the 1988/89 level of asthma hospitalization rate was seen; however, the mean length of stay was shorter than in the preceding period. The decrease in mean length of stay is consistent with that reported elsewhere for Canada.¹⁸

Our analysis has confirmed the differences according to age and sex that have been found in previous studies.^1,8 Longer mean hospital stays were associated with individuals less than 1 year old and those over 75. There was an interaction of the variables of age and sex with respect to length of hospital stay: mean stays were relatively similar until the age of 5, and after that the length of stay was often longer for girls and women. This could be explained by an association between average length of hospital stay and the presence of comorbid conditions, more frequent in older women. Indeed, hospitalizations with a secondary diagnosis were, on average, of longer duration (4.3 days, 95% CI = 4.17–4.34) than those without (2.6 days, 95% CI = 2.52–2.65).

As documented previously,^9,10 most asthma hospitalizations occurred in the fall and the fewest, in the summer. The reduced hospitalization rate in the summer was possibly partially due to holidays and hospital bed closures associated with health care staff reductions. The relatively high numbers in the fall may be associated with increased viral infections occurring near the beginning of the school year¹⁹ and ragweed allergy season (from mid-August until the end of September),²⁰ the asthmatic individual tolerating the reaction for a certain length of time until hospital admission was necessary. An additional cause could be the increased time spent indoors during these fall months, with increased exposure to indoor allergens such as mites and domestic animals.

This seasonal peak does not appear to be an artifact of including patients with chronic obstructive pulmonary disease misdiagnosed as asthma (whose problems may increase in the fall months) because the increase, when analyzed by age group, seemed to be accounted for mostly by children under the age of 10. There was a small rise in the number of admissions in the 40-64-year-old group in September and October, but not in those aged 65 and over (data not shown).

Length of hospital stay was also associated with month of admission, in that the shortest stay was associated with fall admission and the longest with winter admission. Although at first glance this could reflect the availability of hospital beds, since the length of stay appeared to be inversely related to the number of admissions, it was probably more likely due to the increased numbers of hospitalizations of young children during the fall, with their concomitant shorter average stays.

The NIRRU-adjusted cost estimate was higher than that calculated from the average hospitalization cost. Most likely this was due to the ability of the NIRRU to account for the higher cost of days at the beginning of a hospitalization. Asthma hospitalizations are shorter, on average, than overall hospitalizations in Quebec, by almost 50%. Economic evaluations that apply average costs per hospital day could be underestimating the true cost.

The NIRRU index was based upon costs in Maryland, US, and this could limit its usefulness. It is assumed that although the absolute costs per APR-DRG could differ between Maryland and Quebec, the relative costs of one group compared with another should be the same. The adjustments for the Quebec situation did take into consideration differences in the average length of stay between Maryland and Quebec (Quebec hospital stays are normally longer) and the fact that the end of a hospital stay was less resource-intensive than the beginning. There are limitations, however, in using an index based on a different system: we cannot account for structural differences in costs, such as for nursing care and equipment, nor do we have information on the differences between the US and Canada in terms of the severity of the condition of patients admitted to hospital. Even with these limitations, the NIRRU does give us some advantages over a simple per diem, which does not account for differences in resource-intensity during the stay or for differences in severity of illness among patients.

Assuming that Quebec’s hospitalizations represent 21% of those for Canada (based on the rate reported for 1989), the estimate by Krahn et al.¹⁴ for 1990, inflated at 3% per year (or $20 million), is very similar to the estimate we have reached in this study. Their study used a more macro approach, taking the proportion of total Canadian hospital days accounted for by patients with asthma and multiplying this by the aggregate cost data for all Canadian public hospitals. Our research study involved a micro approach, using the Quebec Ministry of Health and Social Services reported cost and length of stay by service and ward, in the majority of cases adjusted specifically for the ward in which the patient was treated. Nonetheless, the current study may have left some asthma hospitalization costs unaccounted for, as we reviewed only short-term hospital centres and only hospitalizations for a period of 30 days or less. However, those hospitalizations not included accounted for less than 1% of the total asthma hospitalizations for 1994/95.

Conclusion

This study shows similar overall rates of hospitalization in 1988/89 and 1994/95, but with an important rise in the rates among very young children. There were decreases in rates in very few age groups. A small decrease in mean length of stay was seen.

Many of the trends and variations in asthma hospital use found in this study have been seen previously and their causes discussed. Certainly, in analyses of institutional database information it is difficult to determine the causes of changing patterns of use. However, even if the increases in rates of hospitalization seen in very young children could be attributed in part to a change in physician practice or an increase in the use of asthma diagnosis, the rate has doubled since the beginning of the decade and should signal an alarm that justifies further investigation.

A one-year cost of $18–21 million may seem high for asthma hospital costs, but it is most likely a considerable underestimation of the true hospital cost because emergency department visits and physician costs were not included in the analysis.

Acknowledgements

Partial funding of this study was provided by Glaxo Canada Inc. Dr Laurier holds the Hoechst Marion Roussel Chair on Use of Medications: Policy and Outcomes at the University of Montreal.

References

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Claudine Laurier, Faculté de pharmacie and Groupe de recherche interdisciplinaire en santé, Université de Montréal, Montreal, Quebec

Wendy Kennedy and André-Pierre Contandriopoulos, Administration de Santé and Groupe de recherche interdisciplinaire en santé, Université de Montréal, Montreal, Quebec

Jean-Luc Malo, Faculté de médecine, Hôpital du Sacré-Cœur, Université de Montréal, Montreal, Quebec

Michèle Paré, Groupe de recherche interdisciplinaire en santé, Université de Montréal, Montreal, Quebec

Daniel Labbé, Direction générale de la planification et de l’évaluation, Ministère de la Santé et des Services sociaux du Québec, Quebec

André Archambault, Faculté de pharmacie, Université de Montréal, Montreal, Quebec

Correspondence: Claudine Laurier, Faculté de pharmacie, Université de Montréal, C.P. 6128, succursale Centreville, Montréal (Québec) H3C 3J7

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