Introduction Airborne irritants and allergens in the workplace can induce and trigger occupational asthma (OA). OA due to sensitisation is associated with an accelerated rate of decline in FEV₁ (100 mls/yr) compared with healthy controls (25 mls/yr)¹, which improves on removal from exposure. We sought to describe the rate of FEV₁ decline in patients with irritant-induced OA before and after their removal from exposure.

Methods Cases of irritant-induced OA reported between 1991 and 2011 were identified from the SHIELD database (a voluntary reporting scheme for OA) and their demographic characteristics and serial FEV₁ measurements were gathered. Generalised estimating equations with an exchangeable correlation structure were used to calculate an average rate of FEV₁ decline for all patients before and after removal from exposure.

Results A total of 526 FEV₁ readings (179 prior to removal, 347 post removal) were gathered from 52 patients. 30 patients had FEV₁ data both before and after removal; 5 patients had FEV₁ data only before removal, and 17 patients had FEV₁ data only after removal; demographics were not significantly different between the groups. FEV₁ decline prior to removal of the irritant was 44 ml/year (95% CI: 32–58) and FEV₁ decline after removal was 49 ml/year (95% CI: 36–62). There was no significant difference between the intercepts of the two lines, implying no improvement in FEV₁ after removal from exposure.

Conclusion In this cohort, irritant-induced OA was associated with an accelerated decline in FEV₁, which persisted after removal from the irritant. These results might be attributed to differences in the underlying pathology of sensitisation and irritant-induced OA, differences in patient behaviour, or differences in treatments offered to the two groups.

Reference

1. Anees W et al. FEV₁ decline in occupational asthma. Thorax 2006;61:751–5