Asthma diagnosis required that three essential clinical features be present: presence of at least three of four typical asthmatic manifestations: (a) episodic cough and/or sputum production; (b) wheezing; (c) nocturnal episodes of cough, wheezing, and breathlessness; and (d) “bronchial irritability,” the patient experiencing respiratory complaints after exposures to various nonspecific irritants, physical factors, and odors; spirometric evidence of the following: (a) variable airflow limitation or(b)a. positive response to an inhaled bronchodilator and/or (c) the confirmation of nonspecific airway hyperresponsiveness by provocation testing; and corroboration that a diagnosis and/or treatment of bronchial asthma had been made by a physician before the USF evaluation. For the provocation testing, a methacholine (or histamine) challenge testing procedure employed the protocol of Juniper et al and Cockcroft et al, aerosolizing increasing concentrations (0.03 mg/mL to 16 mg/ mL) of the test solution using a nebulizer (Wright; S & M Instruments Co Inc; Doylestown, Pa) driven by a compressed air source. Methacholine or histamine challenges were not performed in subjects with significant impairment of lung function.
The 86 patients were classified into one of the three following categories.
1. Allergic occupational asthma (11 patients) criteria consisted of the following: initiation of asthma caused by exposure in the workplace to a sensitizing agent known to cause allergic-type asthma; cases of asthma occurring after a latent period of exposure lasting at least 4 months; and cases with a consistent temporal relationship between attacks of asthma and workplace exposures.
2. Irritant-induced asthma (54 patients) criteria required the following: initiation of asthma was temporally related to an irritant exposure; asthma symptoms developed during the time period that an irritant exposure was taking place; exposures could be either intermittent or continuous in nature; and subjects were excluded if the irritant exposure lasted >16 weeks (4 months) before initiation of asthma. Subjects with preexisting asthma in remission were included if asthma recurred after remission had been present for at least 1 year before the exposure event.
3. Not occupational/environmental exposure-related asthma (21 patients) was characterized by the absence of a consistent exposure history, and the lack of suitable temporal relationship between asthma initiation and a workplace or environmental exposure.