Summary

Asthma is an inflammatory disease of the airways that results in wheezing, coughing and difficulty breathing. These symptoms are accompanied by changes in respiratory function that include airway obstruction and hyperresponsiveness. Cells called eosinophils are generally present in cases of asthma-related inflammation. Occupational asthma (OA) is an asthma caused by an allergy to a product present in the workplace. Exposure to an occupational agent to which the worker is allergic provokes not only reduced respiratory function but also an increase in eosinophilic airway inflammation. However, some people with occupational asthma do not present eosinophilic inflammation when exposed to a substance to which they are allergic. An earlier study suggested that more severe asthma may develop in these people than in those who present eosinophilic inflammation. Airway inflammation can be measured in sputum induced by having patients inhale a saline solution (induced sputum test).

The purpose of this research project was to find out if absence of sputum eosinophilia on exposure to the offending occupational agent at the time of diagnosis can be used to identify workers with a less favourable long-term asthma prognosis even when removed from exposure. Workers diagnosed with occupational asthma based on a specific inhalation challenge (SIC) about five years ago were tested again to compare asthma severity in those who had an eosinophilic response to the SIC to those who had a non-eosinophilic response.

Results
Forty-four subjects who provided a valid sputum sample at the time of diagnosis (before and after the SIC) and at the time of the study were investigated. Of these, fifteen did not have an eosinophilic response at the time of diagnosis, while 29 did have an eosinophilic response to the SIC. At the time of diagnosis, the non-eosinophilic responders had slightly greater airway limitation than the eosinophilic responders, but they did not show more airway hyperresponsiveness.

Five years later, forced expiration volume in one second (FEV1) was lower, airway obstruction was greater and airway hyperresponsiveness was more pronounced in the non-eosinophilic responders. These subjects also tended to have more difficulty controlling their asthma, and non-eosinophilic response was associated with greater progression of airflow obstruction in the follow-up period.

Conclusion
The study results suggest that subjects with occupational asthma who have a non-eosinophilic response have more severe asthma at the time of diagnosis and poorer outcomes over time than those with an eosinophilic response.