Work-related asthma in stainless steel welders, irritant or allergy?

BACKGROUND: Work-related asthma in welders is often thought to be irritant rather than allergic, limiting the availability of surveillance, assisted retraining and compensation. However, excess inflammatory gene activation is a feature of asthma in stainless-steel welders. AIMS: To investigate a cohort of workers exposed to stainless-steel welding fume who have work-related symptoms to assess if their diagnosis best fits irritant or allergic phenotypes or endotypes. METHODS: All workers seen between 2000 and 2021 with confirmed work-related asthma exposed to stainless-steel welding fume were included. The types of exposure responses were identified from Oasys programme plots of 2-hourly peak expiratory flow (PEF) measurements at work and home over 4 weeks. While exposed, non-specific bronchial reactivity (NSBR), atopy, eosinophilia and fractional exhaled nitric oxide (FeNO) were measured. The irritant endotype was defined as (i) absence of relevant immunoglobulin E sensitization; (ii) association with NSBR; (iii) immediate onset of symptoms following exposure; and (iv) either pre-existing asthma or a latency period for symptom onset of <6 months. RESULTS: Twenty-five workers exposed to stainless-steel welding fume showed PEF changes, confirming work-related asthma. A possible irritant endotype was present in four. One had pre-existing asthma, two had latencies of <6 months and three had NSBR. Peripheral eosinophilia and raised FeNO were uncommon. CONCLUSIONS: The phenotype or endotype was incompatible with purely irritant mechanisms in 21 participants and had predominately T helper 2 low inflammatory characteristics. Stainless-steel welders with work-related asthma should be managed as occupational asthma with hypersensitivity.