The aims of the present study were to determine whether exposure to high peaks of ozone resulted in an increased prevalence of asthma or respiratory symptoms among bleachery workers and whether nitric oxide (NO) was elevated in the exhaled air of these workers.Bleachery workers (n=228) from three Swedish pulp mills who had been exposed to ozone, together with 63 unexposed control subjects, were investigated by means of spirometry, Phadiatop1, exhaled and nasal NO and answers to a questionnaire concerning respiratory symptoms and exposure. Exposure to an ozone peak that gave rise to respiratory symptoms was defined as a "gassing".Bleachery workers reporting four or more gassings involving ozone had an increased prevalence of adult-onset asthma, wheeze, and current asthma symptoms. They also had a higher median concentration of exhaled NO in comparison with those who reported no such gassings (19.2 versus 15.7 parts per billion). No such associations were found in respect of nasal NO.The results from this study show that bleachery workers who have been repeatedly exposed to ozone gassings have an increased prevalence of adult-onset asthma. The results also indicate exhaled nitric oxide may be a marker of airway inflammation in bleachery workers who have been exposed to high peaks of ozone.

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