Sixty-three subjects with
occupational asthma caused by crab (n = 31) and various other agents (n = 32) were studied after cessation of exposure at work for mean +/- SD intervals of 12.3 +/- 5.5 and 24.5 +/- 18.7 months (greater than 6 months in every subject), respectively. Nineteen of the subjects with
asthma caused by crab and 30 of the subjects with
asthma caused by various agents were still symptomatic of
asthma, nine subjects of the latter group requiring
bronchodilators (with inhaled
beclomethasone in five) regularly. No significant changes in baseline spirometry were observed at the time of follow-up as compared with initial assessment, nine subjects (all in the
asthma group caused by various agents) demonstrating significant bronchial obstruction. Improvement in bronchial responsiveness to
histamine was significant (p less than 0.01) in the group with
asthma caused by crab but not in the other group. Forty-eight of 52 subjects still had significant airway hyperexcitability. Subjects with
asthma caused by crab who were asymptomatic and those subjects with
asthma caused by various agents who used
bronchodilators only if they were needed had worked for shorter intervals after onset of symptoms (p less than 0.01 and p less than 0.05, respectively). It is concluded that subjects with
occupational asthma caused by various agents can remain symptomatic of
asthma and demonstrate a persistence of bronchial obstruction and hyperexcitability for prolonged intervals after cessation of exposure.