Diisocyanate-induced asthma in Switzerland: long-term course and patients’ self-assessment after a 12-year follow-up

BACKGROUND: Isocyanates are among the most common causes of occupational asthma (OA) in Switzerland. Patients with OA have been shown to have unfavourable medical, socioeconomic and psychological outcomes. We investigated long-term asthma and the socio-economic outcomes of diisocyanate-induced asthma (DIA) in Switzerland. PATIENTS AND METHODS: We conducted an observational study on 49 patients with DIA and followed 35 of these patients over a mean exposure-free interval of 12 ± 0.5 (range 11.0-13.0) years. At the initial and follow-up examinations, we recorded data on respiratory symptoms and asthma medication; measured the lung function; and tested for bronchial hyperreactivity. We allowed the patients to assess their state of health and overall satisfaction using a visual analogue scale (VAS) at these visits. RESULTS: The 35 patients whom we could follow had a median symptomatic exposure time of 12 months, interquartile range (IQR) 26 months and a median overall exposure time of 51 (IQR 104) months. Their subjective symptoms (p < 0.001) and the use of asthma medication (p = 0.002), particularly the use of inhaled corticosteroids (p < 0.001), decreased by nearly 50%. At the same time, the self-assessment of the patients’ state of health and overall satisfaction increased considerably according to both symptomatology and income. In contrast, slight reductions in terms of FVC% predicted from 102% to 96% (p = 0.04), of FEV1% predicted from 91% to 87% (p = 0.06) and of the FEV1/FVC ratio of 3%; (p = 0.01) were observed while NSBHR positivity did not change significantly. In univariate as well as multivariate logistic analyses we showed significant associations between age, duration of exposure and FEV1/FVC ratio with persistent asthma symptoms and NSBHR. CONCLUSIONS: We found that the patients’ symptoms, the extent of their therapy and the decrease in their lung volumes during the follow-up period were similar to the findings in the literature. The same hold true for some prognostic factors, whereas the patients’ self-assessment of their state of health and overall satisfaction improved considerably.