Chest
Volume 126, Issue 4, October 2004, Pages 1147-1153
Journal home page for Chest

Clinical Investigations
ASTHMA
Risk of Physician-Diagnosed Asthma in the First 6 Years of Life

https://doi.org/10.1378/chest.126.4.1147Get rights and content

Objective:

The objective of this cohort study was to determine if complications of pregnancy and labor, characteristics at birth, and exposure to infections influence the incidence of asthma in the first 6 years of life.

Design:

We identified all children born between 1980 and 1990 in the Province of Manitoba, Canada. We used records of physician contacts (inpatient and outpatient) and services of the universal provincial health insurance plan to follow up 170,960 children from birth to the age of 6 years to identify the first diagnosis of asthma. Information on mothers and siblings was also obtained to determine family history of disease and exposure to infections.

Results:

During the study period, a diagnosis of asthma was made in 14.1% of children by the age of 6 years. The incidence was higher in boys than in girls, in those with family history of allergic diseases. It was higher in urban than in rural areas, and lowest in those born in winter. Asthma was more likely in those with low birth weight and premature birth. Certain congenital abnormalities and complications of pregnancy and labor also increased the risk of asthma. The risk of asthma increased with maternal age. Both upper and lower respiratory infections increased the risk of subsequent asthma, and this effect was more important than exposure to familial respiratory infections, which also tended to increase asthma risk. The risk of asthma decreased with the number of siblings when siblings had a history of allergic disorders.

Conclusions:

In addition to genetic influences, intrauterine and labor conditions are determinants of asthma. Exposure to both upper and lower respiratory tract infections increases the risk; these infections do not explain the protective effect associated with the increasing number of siblings.

Section snippets

Database

The Province of Manitoba has a relatively stable population of approximately 1.2 million people, and a universally accessible health-care system with fee for service as the method of physician payment. Payments depend on submission of claims that include the diagnosis, type of service, and the patient's identifier, date of birth, gender, and residential postal code. There is no record of ethnicity. Nonnominal records of medical services, including hospitalizations, are stored in the Manitoba

Results

There were 170,960 newborns followed up to their sixth birthday. Of these, 24,026 newborns (14.1%) were seen for asthma. The incidence was the highest in the first 2 years of life (2.6% and 2.9%, respectively) and declined to 2.0% in years 5 and 6. The cumulative incidence increased 2.3 times (95% CI, 2.2 to 2.5) from the cohort born in 1980 to that born in 1990.

Tables 1234show variables with significant HRs for the incidence of asthma. These HRs were derived from the model that included all

Discussion

There are several weaknesses associated with using administrative databases to study asthma. The first is the diagnosis of asthma. There is no objective test for asthma in children,15 and there may be labeling problems in relation to related diseases. We relied on the diagnosis submitted by the physician for payment of services. We defined the onset of asthma in three different ways and carried out analyses with each definition as the outcome. Because the same variables were identified as risk

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    Support was provided by the Medical Research Council Canada.

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