Study objective: To test the hypothesis that work as a respiratory therapist is associated with an increased risk of developing asthma.
Design: Cross-sectional questionnaire study comparing respiratory therapists with controls (physical therapists and radiologic technologists). Subsequent validation of reported asthma with methacholine challenge studies.
Subjects: All respiratory therapists and physical therapists and a random 50% sample of radiologic technologists working in the state of Rhode Island as of June 1986.
Methods: All subjects received a mail questionnaire with questions about the presence or absence of asthma, time of onset, and important covariates. Responses were analyzed for all subjects, and again after excluding those subjects with pre-existing asthma. Subjects who reported physician-diagnosed asthma were asked to have methacholine challenge testing.
Results: Respondents included 194 respiratory therapists (response rate, 69.5%) and 517 controls (response rate, 75.3%). After excluding respiratory therapists from the hospital at which the hypothesis was generated, there were 34 respiratory therapists (18.7%) and 30 controls (5.8%) reporting physician-diagnosed asthma. After controlling for age, smoking status, family history, atopic history, and other covariates using logistic regression, respiratory therapy carried an odds ratio of 3.2 (95% CI, 1.9 to 5.5). With analysis restricted to those who developed asthma after entering their profession, the odds ratio for respiratory therapy was 4.6 (95% CI, 2.0 to 10.4). In the validation study, 10 of 14 respiratory therapists (71%) and 6 of 10 controls (60%) had evidence of bronchial hyperreactivity.
Conclusions: These results suggest a previously unrecognized excess of asthma in respiratory therapists. The excess develops after entry into the profession, and does not appear to be explained by confounding, information bias, or selection bias.