A review of epidemiological methods applied in studies on laboratory animal allergy. With a discussion of the relation between prevalence and risk of an irreversible disease in a dynamic population of constant size.

The risk of developing an occupational allergic respiratory disease depends strongly on the duration of exposure. For estimating the instantaneous risk (hazard function) in a dynamic cohort, information is required for each cohort member on the time of exposure either until disease onset or until termination by leaving the job or the end of the study. However, most existing epidemiological studies on occupational allergies are cross-sectional, computing prevalences; no information on job-leavers and on their disease status is obtained. The functional dependency of prevalence on risk, as well as on the rate of leaving the job among the diseased and on the distribution of exposure duration, is described, with special attention to the sensitivity of the prevalence to differences of the rate of leaving the job. A literature review of 15 studies on laboratory animal allergy is given; none of the studies collected and reported all the information necessary for risk estimation.