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(Chest. 2003;124:438-448.)
© 2003 American College of Chest Physicians

Stabilization of an Increasing Trend in Physician-Diagnosed Asthma Prevalence in Saskatchewan, 1991 to 1998*

Ambikaipakan Senthilselvan, PhD; Joshua Lawson, MSc; Donna C. Rennie, PhD and James A. Dosman, MD, FCCP

* From the Department of Public Health Sciences (Dr. Senthilselvan), University of Alberta, Edmonton, AB, Canada; and the Institute for Agricultural Rural and Environmental Health (Mr. Lawson, and Drs. Rennie and Dosman), University of Saskatchewan, Saskatoon, SK, Canada.

Correspondence to: A. Senthilselvan, PhD, Department of Public Health Sciences, University of Alberta, 13-106D Clinical Sciences Bldg, Edmonton, AB, Canada T6G 2G3; e-mail: sentil{at}ualberta.ca


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Objectives: To determine the prevalence of asthma, bronchitis, and COPD using the physician services database of the Saskatchewan Health Department from 1991 to 1998.

Design: Descriptive population-based study.

Setting: The Province of Saskatchewan, Canada.

Participants: Residents of Saskatchewan covered by universal health care in the province.

Results: In all age groups, asthma prevalence increased between 1991 and 1995 and either was stable or declined between 1996 and 1998. Preschool children had the highest asthma prevalence during the study period, followed by children aged 5 to 14 years, young adults aged 15 to 34 years, and adults aged 35 to 64 years. Children aged 0 to 4 years and adults aged 35 to 64 years in the Registered Indian population had greater asthma prevalence than persons in other urban or rural populations during the study period. Asthma prevalence rates in rural populations were less than or similar to the rates of urban populations in all age groups during the study period. The prevalence of bronchitis was greater in the Registered Indian population than in urban and rural populations in all age groups throughout the study period. When persons who had visited a physician for bronchitis were excluded from the prevalence calculation, the original increases seen in asthma prevalence among very young children and older adults of Registered Indian origin disappeared, with the urban population having greater asthma prevalence in all age groups. In the Registered Indian population, adults aged 35 to 64 years had almost twofold increases in the prevalence of COPD in comparison to other Saskatchewan populations.

Conclusions: Asthma prevalence, which had been on the increase in the 1980s and early 1990s, was either stable or declining during the latter part of 1990s in Saskatchewan. Preschool children and older adults from the Registered Indian population had greater asthma prevalence than did those from other Saskatchewan populations. Asthma prevalence among the rural populations was either similar or lower in comparison to the rates for the urban populations in all age groups during the study period. Further research is required to elucidate the findings in this study.

Key Words: American Indians • asthma • bronchitis • COPD • prevalence • rural • sex • trend


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Asthma prevalence has been increasing in the last 2 decades among children in developed countries including Canada and the United States.1 2 Asthma hospitalization rates, however, have shown a decline in recent years in Canada and the United States.1 2 In the International Study of Asthma and Allergies in Childhood (ISAAC), which was conducted in 91 centers from 38 countries among children 6 to 7 years old and in 155 centers from 56 countries among children 13 to 14 years old, cumulative asthma prevalence ranged between 1.3% and 30.8% in younger children, and between 1.4% and 30.2% in older children.3 In the ISAAC study, the cumulative prevalence of asthma was found to be greater in English-speaking and Latin American countries. In the ISAAC study conducted in the Canadian centers, asthma prevalence in children 6 to 7 years old was 11.2% in Saskatoon and 17.2% in Hamilton, while in children 13 to 14 years old it was 12.2% in Saskatoon and 19.2% in Hamilton.4 In a study5 of adults aged 20 to 44 years that was conducted in six cities in Canada using the sampling strategy and standardized questionnaire of the European Community Respiratory Health Survey, asthma prevalence varied between 4.4% and 6.3% in men, and 5.2% and 9.5% in women.

Several studies have reported lower asthma prevalence among rural populations.6 7 8 Children living on farms were reported to have a lower prevalence of asthma and allergy in comparison to those children living in a nonfarming environment.9 10 11 12 13

Asthma prevalence was reported to be greater in non-white children than in white children.14 However, some of the racial differences in asthma prevalence were attributed to income, area of residence, and level of education.14 Only a few studies have investigated asthma morbidity among American Indians. In a reanalysis15 of the 1987 Survey of American Indians and Alaska Native children aged 1 to 17 years, asthma prevalence was reported to be 7.06%, which was slightly lower than that reported for the US population. However, the same group of researchers conducted a retrospective analysis16 of Washington State hospitalization data for 1987 through 1996, and reported that hospitalization rates for asthma and bronchiolitis among American Indian and Alaska Native children who were aged > 1 year were two to three times greater than that observed for all other children combined. In a study conducted in Saskatchewan, Registered Indians and other Saskatchewan children < 4 years of age had similar asthma hospitalization rates in the early 1970s (range, 0.41 to 0.63%), but this pattern changed in the late 1980s with Registered Indian children having three times greater asthma hospitalization rates than those observed in other children in Saskatchewan.17 These differences were not seen in older children.

In a previous study, we investigated trends and age-sex differences in asthma prevalence from 1981 to 1990 using the physician services database of the Saskatchewan Health Department.18 Asthma prevalence increased in all age groups during the study period in Saskatchewan.18 In this manuscript, we use the data from the physician services database to determine asthma prevalence with and without a diagnosis of bronchitis for both Registered Indian and other urban and rural populations in the Province of Saskatchewan from 1991 to 1998. To determine the number of asthma-related drug purchases by persons with physician-diagnosed asthma, asthma visits were linked to the outpatient prescription drug database. Asthma-related drug purchase then was used to determine the accuracy of the asthma diagnosis. For comparison with asthma prevalence, we also determined the prevalence of bronchitis and COPD among Registered Indian and other rural and urban populations in Saskatchewan.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Saskatchewan Population
As reported in the 1996 census, the population of Saskatchewan was composed of 976,615 persons, which included people of European origin (81.7%), aboriginal origin (11.4%), and other single (2.3%) and multiple (4.7%) origins.19 20 The Registered Indians of Saskatchewan are of aboriginal origin and have registered under section 6 of the Indian Act with the Federal Government of Canada. This population is made up of mainly Cree and Chipewyan origins, and a small number of Saulteaux, Assinibione, Dakota, Ojibwa, and Dene origins. The Federal Government is responsible for the health, education, and welfare of Registered Indians. In 1998, the population of Registered Indians in Saskatchewan was 87,310 persons.21 Of this population, about 50% lived on the reserves, while the rest lived in urban areas of Saskatchewan.22

Saskatchewan Health Databases
All residents of Saskatchewan, except members of the Royal Canadian Mounted Police, members of the Canadian Forces, and inmates of federal penitentiaries, are eligible to receive universal health coverage from the Provincial Government. The excluded group is about 1% of the Saskatchewan population. Each eligible Saskatchewan resident receives a health services card that contains a unique nine-digit health services number. The Person Registry System is a central computer file that contains the unique health services number, name, address, sex, date of birth, and dates of health coverage initiation and termination. This file is updated daily for name or address changes, births, deaths, and new arrivals and departures from the province.23 The physician services database contains information sent by physicians for medical services rendered to patients. Visits to emergency departments are captured in this database only when nonsalaried physicians attend to these patients. The outpatient prescription drug database includes information of all prescription drugs listed in the Saskatchewan Formulary and purchased by Saskatchewan residents, excluding the Registered Indian population who are covered by the Federal Government of Canada. Under the Prescription Drug Plan, Saskatchewan residents receive benefits from the Provincial Government, which include copayments for drugs when a family exceeds a deductible amount. The Provincial Government made major changes to the deductibles and copayments under the Prescription Drug plan in 1987, 1991, 1992, and 1993.24

Identification of Asthma, Bronchitis, and COPD Cases
For each year, from January 1, 1991, to December 31, 1998, data on all visits to physicians for the treatment of asthma, bronchitis, and COPD were abstracted from the physician services database using the following International Classification of Diseases, ninth revision (ICD-9), clinical modification codes: asthma (ICD 493); bronchitis, which included acute bronchitis and bronchiolitis (ICD 466); bronchitis not specified as acute or chronic (ICD 490); and COPD, which included chronic bronchitis (ICD 491), emphysema (ICD 492), and chronic airway obstruction, not elsewhere classified (ICD 496). The primary diagnosis for each visit is determined by physicians to support the claim for payment. The claims that are submitted electronically to the Medical Services Branch include ICD-9 codes, which are assigned by persons working at physician practices. Claims not submitted in electronic form would include a written diagnosis, and then trained coders within the Medical Services Branch of Saskatchewan health would assign the specific ICD-9 code. During the early period of the study, the majority of claims would have been submitted in paper form and the coding would have been done in the Medical Services Branch.

For each visit, the following information was obtained: pseudo-identification number; age (5-year age categories from 0 to 64 years and an indicator for > 65 years); sex; residence type (cities with population > 10,000, towns that are either large city neighborhoods or cities with populations of < 10,000, and other areas which did not fall into any of the above categories); health district; Registered Indian status; physician specialty; service date; and primary diagnosis (three-digit ICD-9 code). A subject with at least one visit to a physician for asthma (ie, bronchitis or COPD) during the index year was defined as a case of physician-diagnosed asthma (ie, bronchitis or COPD) in that year.

Definition of Rural and Urban Populations
A rural population included all persons except Registered Indians living in rural towns or cities with populations of < 10,000. An urban population included all persons except Registered Indians living in cities with populations of >= 10,000.

Prevalence Estimation
If a subject made more than one physician visit in a calendar year, only the first visit was considered for a prevalence estimation of that calendar year. The total number of first visits formed the numerator of the prevalence estimate, while the denominator was obtained from the person registry system. Age-specific, sex-specific, and study group-specific prevalence estimates were obtained for each calendar year from 1991 to 1998.

Verification of Asthma Diagnosis
For each calendar year, asthma cases, excluding Registered Indians, identified from the physician services database were linked to the outpatient prescription drug database to check whether they had purchased an asthma-related drug during the 12-month period following the (first) visit. Asthma-related drugs included short-acting inhaled and oral ß2-agonists, long-acting inhaled ß2-agonists, methylxanthine, ipratropium bromide, ipratropium/salbutamol, inhaled corticosteroids, oral corticosteroids, sodium cromoglycate, nedocromil, and ketotifen. The age-specific and sex-specific proportion of asthma patients with evidence of an asthma-related drug purchase was used as an indicator of accuracy of asthma diagnosis in our study. For prevalence estimation, we included all persons regardless of whether they had evidence of an asthma-related drug purchase or not. Since the study ended on December 31, 1998, asthma cases identified during 1998 did not have a 12-month period following the first visit, which in turn resulted in a slight underestimate of the proportion of asthma cases with evidence of an asthma-related drug purchase in that year.

Statistical Analysis
In each age group, a Poisson regression analysis was used to test the association between asthma prevalence and sex, study group, and calendar time.25 The strength of association was described using rate ratios with 95% confidence intervals.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Asthma Prevalence
As shown in Figure 1 , asthma prevalence rates were highest in preschool children aged 0 to 4 years during the study period, followed by school-going children, young adults, and older adults. This pattern was consistent throughout the study period. There was a rapid increase in asthma prevalence rates from 1991 to 1995, and a steady increase from 1996 to 1998 among preschool children as well as young adults and older adults. In school-going children aged 5 to 14 years, an increase was observed in asthma prevalence rates from 1991 to 1995, which was followed by a decrease in rates from 1996 to 1998. In 1998, physician-diagnosed asthma prevalence rates were 8.1% in preschool children (0 to 4 years), 5.9% in school-going children (5 to 14 years), 3.5% in youths and young adults (15 to 34 years), and 2.7% in older adults (35 to 64 years).



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  		Figure 1.. Age-specific prevalence rates of physician-diagnosed asthma in Saskatchewan, 1991 to 1998.

 
Sex Distribution of Asthma Prevalence
Asthma prevalence rates were greater in boys than in girls for preschool and school-going children, but this pattern was reversed in young and older adults with women having a greater prevalence of asthma than men (Fig 2 ). Although Figure 2 depicts this pattern among the total Saskatchewan population for 1998, a similar pattern was seen for other calendar years and for persons in the Registered Indian, urban, or rural population in Saskatchewan.



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  		Figure 2.. Prevalence of asthma by age group and sex in Saskatchewan, 1998.

 
Asthma Drug Purchases
The proportions of asthma subjects who purchased an asthma-related drug during the first 12 months following their visit to a physician are given in Table 1 for each age group and calendar year. In all age groups, about 70% of the asthmatic patients purchased at least one asthma-related drug during the study period. A slightly greater proportion of asthmatic patients in the adult groups compared to the younger age groups purchased at least one asthma-related drug.


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  		Table 1.. Distribution of Physician-Diagnosed Asthma and Evidence of Asthma Drug Purchase by Age and Calendar Year in Saskatchewan, 1991–1998*

 
Asthma Prevalence by Registered Indian Status
In Figure 3 , asthma prevalence rates are shown for the Registered Indian population and other populations living in urban and rural areas of Saskatchewan. In preschool children and adults aged 35 to 64 years, asthma prevalence rates were greater among the Registered Indian population than among the non-Registered Indian population living in urban and rural areas from 1991 to 1998. In other age groups, this pattern was reversed, with urban and rural populations having higher rates of asthma prevalence than the Registered Indian population. In comparison to the urban population, the rural population had lower asthma prevalence rates in all age groups from 1991 to 1998. These differences are further quantified by the adjusted odds ratios and 95% confidence intervals, which are given in Table 2 . Preschool children from the Registered Indian group are 1.39 times more likely to receive diagnoses of asthma than are other children in Saskatchewan, while Registered Indians in the group who were 35 to 64 years of age were 1.49 times more likely to receive a diagnosis of asthma than were other persons in that age group. In all age groups, the rate ratios of asthma diagnosis for the rural population, in comparison to the urban population, are < 1, confirming the protective effect of rural dwelling for asthma diagnosis that is seen in Figure 3 .



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  		Figure 3.. Age-specific prevalence rates of physician-diagnosed asthma in the Registered Indian population, and in other urban and rural populations in Saskatchewan, from 1991 to 1998.

 

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  		Table 2.. The Association Between Asthma and Demographic Factors Obtained From Age-Specific Multivariate Poisson Regression Analyses*

 
Bronchitis Prevalence
In all age groups, prevalence rates of bronchitis decreased from 1991 to 1998 among Registered Indian, urban, and rural populations. Prevalence rates for bronchitis were greater in the Registered Indian population than in the urban or rural populations in all groups (Fig 4 ), whereas asthma prevalence rates for the Registered Indian population were greater only in preschool children and older age groups. In 1998, physician-diagnosed bronchitis prevalence rates among Registered Indians were 31.8% in preschool children (0 to 4 years), 15.6% in school-going children (5 to 14 years), 13.7% in youths and young adults (15 to 34 years), and 22.6% in older adults (35 to 64 years), which were two to three times greater than those observed in rural and urban populations.



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  		Figure 4.. Age-specific prevalence rates of physician-diagnosed bronchitis in the Registered Indian, and in other urban and rural populations in Saskatchewan, from 1991 to 1998.

 
Asthma Prevalence Excluding Bronchitis
In Figure 5 , asthma prevalence is shown for the Registered Indian population and for other populations in urban and rural areas, after excluding persons who also had a visit to the physician for bronchitis during the same calendar year. The pattern seen in Figure 3 is changed in the groups who were 0 to 4 years of age and 35 to 64 years of age, with the urban population having higher asthma prevalence than the Registered Indian population.



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  		Figure 5.. Age-specific prevalence rates of physician-diagnosed asthma without a physician visit for bronchitis in the Registered Indian, and in other urban and rural populations in Saskatchewan, from 1991 to 1998.

 
COPD Prevalence
The prevalence rates of COPD decreased from 1991 to 1998 in all three study groups. Children and young adults of Registered Indian origin had greater COPD prevalence rates than did other urban and rural populations from 1991 to 1997, and this pattern was reversed in 1998 with urban population having greater or almost equal prevalence of COPD. However, COPD prevalence rates were greater throughout the study period among older Registered Indian populations (Fig 6 ).



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  		Figure 6.. Prevalence of COPD in the Registered Indian, and in other urban and rural populations in Saskatchewan, from 1991 to 1998.

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
In our study, we used the physician services database of the Saskatchewan Health Departments to estimate the period prevalence of asthma from 1991 to 1998. The period prevalence estimates of 8.1% in preschool children (0 to 4 years) and 5.9% in school-going children (5 to 14 years) in 1998 from our study are consistent with those of a Canadian cross-sectional study,1 which reported a lifetime asthma prevalence of 10% among children aged 0 to 14 years of age.

In our previous report,18 asthma prevalence increased from 1981 to 1990 in all the age groups in Saskatchewan. In the present study, this trend continued until 1996, and thereafter asthma prevalence was either stable or decreased in 1997 and 1998. In a report of the National Health Interview Survey by the US Centers for Disease Control and Prevention,26 the annual rates of asthma episodes or attacks between 1997 and 1999 were lower than the rates reported for previous years. These findings indicate that the increasing trend seen in asthma prevalence in the last 2 decades has entered into an apparent decline. The reasons for the decline in asthma prevalence are not known, however, they may be related to new asthma medications and to improved self-management or parental management of asthma.

In our study, asthma prevalence was greater in boys than in girls until the age of 15 years, and it was reversed in young and older adults with women showing greater prevalence than men. This was true not only in the whole Saskatchewan population, but also in the Registered Indian, urban, and rural populations. This is a well-known finding, and several studies have made similar observations.1 2 4 5 18 26 27 The reasons for the sex differences in asthma prevalence are not known. However, smaller airways relative to the lung volume in boys and differences in hormonal changes between male children and female children at puberty have been investigated as possible pathophysiologic mechanisms for the sex differences in asthma prevalence.28

In the Registered Indian population in Saskatchewan, asthma prevalence was greater among preschool children and older adults throughout the study period from 1991 to 1998 in comparison to rural and urban populations. Interestingly, we observed similar patterns in asthma hospitalization rates among the Registered Indian population, although the study periods were different (1991 to 1998 vs 1970 to 1989).17 In a recent study29 conducted in the Province of Alberta, young children and older adults from the aboriginal population had greater age-standardized rates for emergency department visits and physician office visits for asthma or COPD than those rates in non-aboriginal populations. However, when persons with visits to physicians for both asthma and bronchitis were removed in each calendar year, preschool children from urban areas showed evidence for greater asthma prevalence than preschool children of Registered Indian origin. Therefore, we cannot rule out the possibility of physician labeling of bronchitis as asthma as a possible reason for the observed increases in asthma prevalence among preschool children of Indian origin. This might be an underestimate, however, as it would be possible for an individual to have both asthma and bronchitis, resulting in a visit for both in a calendar year.

In a 2000 study conducted among American Indian and Alaska Native children using Washington State hospitalization data for 1987 through 1996, asthma and bronchiolitis hospitalization rates for Indian children aged 1 to 4 years were similar to the rates of all children in Washington State, whereas in children < 1 year of age, these rates were two to three times greater in American Indian and Alaska Native children in comparison to the rates for all children in Washington State.16 In a previous study,15 the same group of researchers reported that asthma prevalence in American Indian children and Alaska native children aged 1 to 17 years was 7.06% in 1987, which was similar to the asthma prevalence in the United States (8.40%). In a 2001 survey30 of American Indian children and Alaska Native children aged 11 to 16 years, asthma prevalence was 2.3 times greater in metropolitan Tacoma, WA, than in a nonmetropolitan area of Alaska. In our study, differences in the prevalence rates of reported COPD between Registered Indian and other populations were similar to that of asthma prevalence for the four age groups. In contrast, the prevalence rates of bronchitis were greater in the Registered Indian population than in other Saskatchewan populations in all age groups throughout the study period.

These higher bronchitis prevalence rates among the aboriginal population may be related to higher rates of smoking, which is reported to be about 71 to 72% in young adults aged 20 to 29 years, which is almost double the overall rate of the Canadian population.31 32 The possibility of differences in the preventive injection of flu vaccination between aboriginal and other populations explaining the differences in the observed bronchitis rates cannot be ruled out. In Saskatchewan, flu vaccinations are provided free of charge to persons aged >= 65 years, and for a small charge to persons < 65 years of age. From 2000 to 2001, 155,000 persons (about 15.8% of the total population) received the flu vaccine in Saskatchewan,33 and, interestingly, in the same year, the population of persons aged >= 65 years was about 15.1% of the total population,34 which suggests that only a small percentage of persons < 65 years of age might have had the flu vaccination. Since our study included only persons aged <= 64 years, it is very unlikely that differences in flu vaccination rates between the aboriginal and other populations could have resulted in the higher bronchitis rates for the aboriginal population.

The aboriginal population in Canada, which includes Registered Indians, has lower income and lower educational attainment in comparison to the non-aboriginal population in Canada.35 The living conditions of the aboriginal population are different from those of other populations in Canada. The homes of persons in the aboriginal population are overcrowded, and children are exposed to passive smoking in these homes. In a recent report on the 1996 Census,36 31% Registered Indian households had more than one person per bedroom, whereas only 14% of non-aboriginal households had more than one person per bedroom in the Province of Manitoba. In a study37 conducted among Inuit school children from northern Quebec, atopy, determined by skin-prick tests, was found in only 5.3% of children, and mite allergens were almost absent in 50 house dust samples taken from the mattresses and bedroom floors from the homes of these children. In our study, only the preschool children and older adults from the Registered Indian population had greater asthma prevalence than did other Saskatchewan populations, indicating that biological age could be more important than race, socioeconomic status, and indoor allergen exposure in explaining the observed variations in asthma prevalence between the Registered Indian and other populations in Saskatchewan. In a study conducted in Montreal, Canada,38 socioeconomic status indicated by parental occupation was not associated with asthma or wheeze prevalence. These findings are different from those reported in studies conducted in the United States, where minorities with diverse ethnic and racial background, and persons with lower socioeconomic status had increased asthma morbidity in comparison to white populations with higher socioeconomic status.39 The reasons for this difference are not known but might include access to health care and exposure to indoor environmental allergens. Registered Indian and other populations have access to universal health care in Canada, whereas only a subgroup of the population has access to adequate health care in the United States.40 A 2001 study41 reported that African-American children are more likely to be sensitized to dust mite or cockroach allergens than are other children in the United States.

In our study, the rural population had either similar or lower asthma and bronchitis prevalence rates than did the urban population in all age groups. Several studies from Europe6 7 8 have reported a lower prevalence of asthma and allergy among children living in rural areas than in urban areas. Although the reasons are not known for the apparent lower prevalence of asthma in rural areas in our study, the majority of persons in rural areas of Saskatchewan live either on a farm or in the vicinity of farms. These persons may be exposed to bacterial compounds from animals that were raised on farms during their early childhood and might be at reduced risk of developing asthma.9 10 11 12 13

Several studies have used administrative databases to determine asthma prevalence,18 42 43 and risk factors for asthma.44 45 The Saskatchewan population receives universal health care by means of a Provincial Government agency, and the physician services database used in our study includes almost all asthma visits to physicians for the total study period. However, one of the limitations of our study was that a physician-billing database was used to determine the prevalence of asthma, bronchitis, and COPD. A single three-digit ICD-9 code was used to indicate the primary diagnosis, regardless of other conditions that patient may have had. The ICD-9 code is determined from the information on physician billing data or is assigned by the staff at the physician services department, and if an asthma episode was related to bronchitis, there might have been a misclassification in the coding between asthma and bronchitis or between COPD and bronchitis. Different diagnostic criteria between physicians may have affected how the visit was coded. In order to verify the accuracy of the asthma diagnosis, we used asthma-related drug purchase to determine the accuracy of asthma diagnosis and documented that > 70% of the persons had purchased at least one asthma-related drug in the 12 months following a visit to the physician. The reasons for the other 30% of the population having no record of purchasing an asthma drug are not known but might include mild asthma not requiring an asthma medication, asthma subjects not purchasing medication prescribed by the physician (noncompliance), or coders assigning the asthma code for other conditions.

We conclude that, first, asthma prevalence, which was on the increase in the 1980s and early 1990s, either stabilized or declined during the latter part of 1990s in Saskatchewan. Second, preschool children and older adults of Registered Indian origin had increased asthma prevalence. Finally, during the study period, rural populations in Saskatchewan had similar or lower asthma prevalence in comparison to urban populations in all age groups. Further research is required to elucidate the findings in this study.


   Acknowledgements
 
The authors thank Winanne Downey of Research Services, Population Health Branch, Saskatchewan Department of Health for assistance with abstracting the data and reviewing the manuscript.


   Footnotes
 
Abbreviations: ICD-9 = International Classification of Diseases, ninth revision; ISAAC = International Study of Asthma and Allergies in Childhood

The research was supported by a grant from the Health Services and Utilization Research Commission, Saskatchewan, Canada.

This study is based in part on nonidentifiable data provided by the Saskatchewan Department of Heath. The interpretations and conclusions contained herein do not necessarily represent those of the Government of Saskatchewan or the Saskatchewan Department of Health.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (e-mail: permissions{at}chestnet.org).

Received for publication June 27, 2002. Accepted for publication January 8, 2003.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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