Original articleSex difference in hospitalization due to asthma in relation to age
Introduction
Asthma is a multifactorial disease, and its genetic and environmental risk factors have not been fully understood. Sex and age are important determinants of asthma occurrence and hospitalization, and the effect of sex on asthma varies with age. Several epidemiologic studies have documented sex differences in asthma prevalence, incidence, and hospitalization, and these differences change considerably over the life span 1, 2, 3, 4, 5, 6, 7. Results from previous studies are consistent for young children that boys have a higher risk of asthma compared with girls, and such a difference is more pronounced in early childhood 1, 2, 3, 4, 5, 6. The influence of sex on asthma has a different pattern among adolescents and adults. Somehow the sex difference in asthma risk disappears during puberty, and then adolescent girls overtake adolescent boys and have more asthma [7]. Greater prevalence [5], incidence [6], and hospitalization [2] of asthma have been found in women than in men. However, it is not clear if the sex difference stays similar in adults across ages.
The aim of this analysis was to examine the interrelationship among sex, age, and hospitalization due to asthma using a national hospitalization database, which contained almost all hospitalizations of the Canadian residents over a 3-year period, with an individual linkage using a standardized health identification number (HIN). Because of the large size of study population, we were able to observe detail changes in the incidence of asthma hospitalization over the life span in both sexes. We discussed a number of hypotheses for such sex- and age-related changes in asthma hospitalization.
Section snippets
Methods
We used the hospital discharge (separation) data collected by the Canadian Institute for Health Information. Each record contains information abstracted from a patient's hospital chart, and pertains to one hospital stay. These records were subjected to linkage procedures to create person-oriented information on patients diagnosed with asthma. Hospital records for each province for the fiscal years 1994/1995 to 1996/1997 were linked using patient identification numbers. The information is
Results
There were approximately 9.5 million hospitalizations with a valid HIN from 1994/1995 to 1996/1997 in Canada excluding Yukon Territory. Table 1 shows that 3.0% of these hospitalizations had asthma listed as one of the first five underlying diagnoses, and 1.5% had asthma listed as the first underlying diagnosis. The proportion of asthma hospitalization, either broadly or narrow defined, was constant across the 3-year study period, while the number of both total hospitalizations and
Discussion
Asthma is an important disease that imposes a heavy burden on the health care system in all countries studied [9]. In an analysis based on the 1987 National Medical Expenditure Survey in the Unite States, Smith et al. [10] estimated direct expenditures of $5.1 billion and indirect expenditures of 673 million in 1994 U.S. dollars for asthma in that country, with a significant portion of the expenditures being accounted for by hospitalizations. In Canada, the total costs of asthma in 1990 were
Acknowledgements
Yue Chen is a Canadian Institutes of Health Research Investigator Award recipient. The authors thank Gary Catlin and Cyril Nair for their helpful comments, and Peter Walsh, John Menic, and Trong Huynh for their assistance in data access and computing.
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