Table 1.

Ascertainment criteria used to define asthma in the cohort

Patients were considered to have definite asthma if a physician made a diagnosis of asthma and/or if each of the following 3 conditions were present. Patients were considered to have probable asthma if the first 2 of the following 3 conditions were present: History of cough with dyspnea and/or wheezing, OR history of cough and/or dyspnea plus wheezing on examination Substantial variability in symptoms from time to time or periods of weeks or more when symptoms were absent Two or more of the following: Sleep disturbance caused by nocturnal cough and wheeze, Nonsmoker (14 y or older) Nasal polyps Blood eosinophilia higher than 300/μL Positive wheal and flare skin tests OR elevated serum IgE level History of hay fever or infantile eczema OR cough, dyspnea, and wheezing regularly on exposure to antigen Pulmonary function tests showing one FEV1 or FVC <70% predicted and another with at least 20% improvement to an FEV1 of higher than 70% predicted OR a methacholine challenge test showing ≥20% decline in FEV1 Favorable clinical response to bronchodilator

Patients were excluded from the study if any of these conditions were present: Pulmonary function tests that showed FEV1 to be consistently below 50% predicted or diminished diffusion capacity Tracheobronchial foreign body at or about the incidence date Hypogammaglobulinemia (IgG less than 2.0 mg/mL) or other immunodeficiency disorder Wheezing occurring only in response to anesthesia or medications Bullous emphysema or pulmonary fibrosis on chest radiograph PiZZ α1-antitrypsin Cystic fibrosis Other major chest disease, such as juvenile kyphoscoliosis or bronchiectasis

FVC, forced vital capacity; and FEV₁, forced expiratory volume in one second.