Definition and Classification of Asthma in the Workplace

Abstract

In this chapter, the authors propose and justify the following definition of occupational asthma: Occupational asthma (OA) is a type of work-related asthma that is caused by immunological (identified or presumed) and non-immunological stimuli present in the workplace. Two types of OA are distinguished based on their underlying mechanisms: OA caused by workplace sensitizers: allergic or immunological OA. This category encompasses (i) OA caused by most high- and certain low-molecular-weight agents for which an allergic (immunoglobulin E, IgE-mediated) mechanism has been proven, and (ii) OA induced by specific occupational agents (e.g. diisocyanates, Western red cedar) in which the responsible allergic and immunologic mechanisms have not yet been identified or fully characterized, though such mechanisms are probable. OA caused by irritants: non-allergic or non-immunological OA, irritant-induced asthma. This category includes acute irritant-induced asthma, initially labeled reactive airways dysfunction syndrome (RADS), which may occur rapidly after a single exposure to nonspecific irritants at high concentrations, as originally described by Brooks and coworkers (Brooks SM, Weiss MA, Bernstein IL. Reactive airways dysfunction syndrome (RADS). Persistent asthma syndrome after high level irritant exposures. Chest. 1985;88:376–84), and not-so-sudden RADS in which onset of symptoms is delayed. This type of OA also includes what has been referred to as “possible irritant-induced asthma,” a syndrome mainly identified in epidemiological studies that may follow chronic exposure to moderate or low levels of irritants at work. Activation of preexistent asthma or airway hyperresponsiveness by nontoxic irritants or physical and common environmental antigenic (antigens also present in the general environment) stimuli in the workplace ordinarily is excluded by this definition. Descriptions of work-exacerbated asthma and other asthma-like conditions are also included.