Asthma risk and eosinophilic airway inflammation in allergen-exposed workers

Occupational asthma (OA) accounts for up to 15% of all adult-onset asthma. Though OA is preventable it is under-recognised in the UK. Fractional exhaled nitric oxide (FENO) is a non-invasive measure of eosinophilic airway inflammation used in asthma management, but its use in occupational settings is debated. In order to understand asthma risk and the role of airway inflammation in allergen-exposed workers, this thesis examined two hypotheses: firstly, that risk of respiratory symptoms and asthma increases with allergen exposure; and secondly, that airway inflammation relates to asthma risk in exposed populations.

A systematic review of asthma risk in woodworkers explores existing evidence for associations between allergen exposure and asthma. Three cross-sectional studies, including 773 workers, examine allergen exposure and asthma, airway inflammation, and lung function in the wood, foundry, and laboratory animal industries.

Symptoms were prevalent but did not clearly relate to allergen exposure. In woodworkers, atopy was the strongest modifier of asthma risk. Airway inflammation was common in foundry workers and related to increasing isocyanate exposure. Laboratory animal workers with more than three years’ exposure had more airway inflammation and poorer spirometry. There was little overlap between airway inflammation and airflow obstruction in symptomatic workers. Airway inflammation significantly increased the risk of work-related symptoms and asthma among symptomatic workers. However, no clear relationship between allergen exposure and airway inflammation was found.

In OA, FENO could be useful in a number of ways: in health surveillance; in asthma diagnosis; and as a measure of allergen exposure. Longitudinal studies are needed to explore how airway inflammation relates to future asthma risk, and to understand how workplace allergen exposures modify airway inflammation in workers at risk of OA.