depends on the abundance and strength of sources as well as dissemination factors, mixing, dilution, and particle removal.

Research Agenda Item: Investigate the dynamics of fungal colonization of indoor reservoirs and emission of allergens from these sources. The results of such research should permit the risks associated with indoor fungal growth to be evaluated.

Exposure to fungal spores (and possibly other fungal antigen-carrying particles) can produce both IgE-mediated disease (e.g., asthma) and hypersensitivity pneumonitis while other allergens (e.g., dust mite, pollen) produce only the IgE-mediated diseases. It is not clear why or under what conditions fungal particles can have this dual effect.

Research Agenda Item: Study the differences between fungal and other allergen-carrying particles that control the development of hypersensitivity pneumonitis as opposed to IgE-mediated asthma.

CHEMICALS

Low-molecular-weight (LMW) chemical agents have been found to cause immunologic disease primarily in the industrial setting but not generally in the office, school, or residential setting. Nevertheless, a variety of household products may contain immunogenic agents such as reactive chemical anhydrides in epoxy resins and isocyanates in bathtub refinishing agents. In addition, chemical allergy in the industrial setting serves as a model for improving our understanding of allergy mechanisms. More than 150 LMW chemical agents have been reported to cause allergic reactions such as asthma and hypersensitivity pneumonitis (Table 3-3; Butcher et al., 1989; Grammer et al., 1989). As industrialization increases and new agents are introduced, the number of chemicals that cause such allergic reactions is likely to increase. Allergic contact dermatitis to these and other chemicals is another type of allergic response found in industrial settings and an important cause of occupational disease; however, it will not be discussed here.

It has been estimated that in industrialized countries 2 percent of asthma is occupationally related (Salvaggio, 1979). The prevalence of occupational asthma varies with the particular chemical. For example, more than half of all workers exposed to platinum salts became sensitized (Cromwell et al., 1979). Among workers exposed to trimellitic anhydride (TMA), approximately 20 percent developed sensitization (Zeiss et al., 1983), whereas approximately 5 percent of toluene diisocyanate (TDI)-exposed workers developed positive inhalation challenge at levels of less than 20 parts per billion (NIOSH, 1978).

For some industries, studies have estimated the prevalence of allergic



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