A comparison of some of the characteristics of patients with occupational and non-occupational asthma.

Occupational asthma is the most frequently diagnosed occupational lung disease reported to the SWORD (Surveillance of Work-related and Occupational Respiratory Disease) scheme. However, diagnosing occupational asthma is not straightforward, and establishing a link with work may be difficult. This study was undertaken to determine the differences between patients with occupational asthma and those with non-occupational asthma which might help in their diagnosis. Information was collected using a self-completed questionnaire. Questionnaires were distributed to 30 subjects aged 18-65 years at each of two clinics--one for patients with occupational asthma and one for those with cryptogenic and environmental asthma. Replies were received from 26 patients with occupational asthma (87%) and 29 patients with non-occupational asthma (97%). The age of onset was significantly higher for those with occupational asthma (42.6 vs 20.7 years). Significantly more subjects with occupational asthma reported improvement on holiday, whereas no significant difference was found in the numbers reporting worsening of symptoms on work days. Those with occupational asthma were less likely to report seasonal variation in symptoms, exacerbation by allergies, pets and stress, or a family history of asthma. Subjects with occupational asthma were more likely to become unemployed (50% vs 3%). Recognition of some of these features in a patient's history may help in the difficult task of differentiating occupational from non-occupational asthma, potentially avoiding the need for exhaustive investigations in some patients. The high prevalence of holiday improvement among subjects with non-occupational asthma suggested that domestic or environmental allergies arising outside the workplace may have been making an important contribution to ongoing symptoms in these subjects.