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An investigation of the increase in preschool-age asthma in Manitoba, Canada
1Canadian Centre for Health Information, Ottawa, Ontario.
Insights
Childhood asthma prevalence increased in Manitoba, Canada. This rise in pediatric asthma cases is linked to diagnostic changes and potential air pollution, not increased severity or healthcare use.
Area of Science:
- Pediatric Respiratory Medicine
- Environmental Health
- Epidemiology
Background:
- Asthma is a significant cause of childhood illness and disability in Canada.
- Hospital admissions for asthma in Canadian children under fourteen rose significantly between 1970-71 and 1987-88.
- Hypotheses for increased asthma prevalence include true increases in disease, or artifacts from changes in detection, diagnosis, treatment, or coding.
Purpose of the Study:
- To review hypotheses explaining the rise in asthma prevalence.
- To test specific hypotheses for children aged 0-4 in Manitoba.
- To estimate asthma prevalence and incidence rates and identify contributing factors.
Main Methods:
- Merged physician claims and hospital separation data to create unique, person-oriented medical records.
- Analyzed data for children aged 0-4 in Manitoba from 1984-85 to 1988-89.
- Estimated prevalence and incidence rates, hospitalization rates, and average hospital stay durations.
Main Results:
- Both asthma prevalence and incidence rates increased for children under five years old.
- Prevalence rates exhibited seasonal peaks in spring and fall.
- No evidence of increased asthma severity was found; hospitalization rates remained stable.
Conclusions:
- Increased preschool-aged asthma in Manitoba is not explained by increased healthcare utilization, coding changes, severity, or income.
- Changes in diagnostic practices appear to contribute to the observed increase in asthma rates.
- Air pollution, particularly ozone (O3) and nitrogen dioxide (NO2), warrants further investigation as a significant contributing factor, especially in spring.
Abstract:
Asthma has long been a major cause of illness and disability among young Canadians. From 1970-71 to 1987-88, hospital admissions for asthma increased significantly among Canadian children under the age of fourteen. Many hypotheses may explain this increase in asthma prevalence. There could be a true increase in the number of people developing symptoms of the disease or increased asthma rates could be an artifact due to changes in detection, diagnosis, treatment, or coding. This study reviews hypotheses put forward to explain the increase in asthma prevalence, and tests some of them in Manitoba for children aged 0-4. Physician claims data and hospital separation data were merged to create unique person oriented medical records. These records were used to estimate the number of children seeking medical services for asthma during a five-year period (1984-85 to 1988-89) and the change in rates over this time period. From 1984-85 to 1988-89, both prevalence and incidence rates for children less than five years of age increased. Prevalence rates showed strong seasonal peaks in the spring and the fall. There is no indication that asthma increased in severity. The hospitalization rate (the number visiting a hospital for asthma divided by the total number seeking medical care for asthma), the average number of hospital admissions per year, and the average number of days spent in a hospital per year did not increase. Levels of ozone (O3) and nitrogen dioxide (NO2) in downtown Winnipeg increased over the study period and asthma prevalence increased twice as fast in Winnipeg as in the rest of the province. For Manitoba, the increase in preschool-aged asthma does not appear to be due to increased use of medical services, a change in ICD coding, an increase in the severity of the cases, or a decrease in income levels. The increases appear to be at least partly due to changes in diagnostic practices. The relationship between asthma and air pollution needs more detailed study as pollution is likely to be an important factor, particularly during the spring. Other areas for further investigation are changes in allergy and virus precursors, maternal smoking, and increased levels of pollens, molds and dust mites.