Incidence and Host Determinants of Probable Occupational Asthma in Apprentices Exposed to Laboratory Animals

Abstract

Laboratory animal (LA) workers are frequently affected with allergic sensitization and occupational asthma (OA). The role of preexposure host factors, in particular airway responsiveness, on the incidence of OA has not been satisfactorily studied. A prospective cohort study of 417 apprentices in animal-health technology was conducted to investigate the incidence and determinants of probable OA. Questionnaire and skin-prick tests with common and work-specific allergens were administered on entry and at follow-up visits (up to three) from 8 to 44 mo after starting apprenticeship. Responsiveness to inhaled methacholine was assessed at baseline and at follow-up in apprentices who developed a new specific skin sensitization and in control subjects. Preexposure host characteristics and the school attended were compared between cases and all cohort subjects not meeting the criteria for probable OA. Twenty-eight apprentices satisfied the definition for probable OA, i.e., onset of immediate skin reactivity to > 1 occupational inhalant and > 3.2-fold decrease in the provocative concentration causing a 20% reduction in FEV(1) (PC(20)). The incidence of probable OA was 2.7% (28/1,043 person-years). Baseline immediate skin reactivity to pets (rate ratio [RR] 4.1, 95% confidence interval [CI] = 1.6 to 10.8), and bronchial responsiveness (PC(20) < or = 32 versus PC(20) > 32 mg/ ml) (RR = 2.5, 95% CI = 1.0 to 5.8) were associated with an increased risk of probable OA; a lower FEV(1) had an apparent, protective effect (RR = 0.58, 95% CI = 0.43 to 0.78). It is concluded that apprentices in animal health show a high incidence of probable OA, and that preexposure airway caliber and responsiveness as well as sensitization to pets are associated with an increased risk.

Have the prevalence and incidence of occupational asthma and rhinitis because of laboratory animals declined in the last 25 years?

“…In all other cross-sectional studies all workers who were exposed to LA were recruited. In the four longitudinal studies it was not possible to show a reduction of incidence over time also because in three, study years were overlapping (Table 2) (24)(25)(26)(27). Only a strong negative cohort effect seemed to emerge in one study, as incidences of OA and OR was inversely correlated with follow-up duration and age (25).…”

“…Between 1983 and 2005 four longitudinal studies evaluated OR and/or OA in workers exposed to LA, allowing incidence estimates (Table 2) (23)(24)(25)(26)(27). Two publications were treated as a single study because the reported analysis came from the same cohort of animal health apprentices (26,27).…”

“…Two publications were treated as a single study because the reported analysis came from the same cohort of animal health apprentices (26,27).…”

“…Among 373 Canadian apprentices in animal health technology without significant previous exposure to LA, who were recruited upon starting their training between 1993 and 1995, the incidence of probable OA and OR was 2.7/100 person years and 11.3/100 person years, respectively (26,27). The follow-up was up to 44 months and the participation rate was 89%.…”

“…To investigate trends in the prevalence and incidence of OA and OR over time, we reviewed the available published literature for both (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27).…”