Hypersensitivity pneumonitis (HP), also called extrinsic allergic alveolitis, is a syndrome characterized by diffuse inflammation of lung parenchyma and airways in response to the inhalation of antigens to which the patient has been previously sensitized. Numerous inciting agents have been described including, but not limited to, agricultural dusts, bioaerosols, and certain reactive chemical species. (See "Epidemiology and causes of hypersensitivity pneumonitis (extrinsic allergic alveolitis)".)
Because both environmental and host factors are involved in the production of the HP syndromes, management theoretically can involve modification of the environment or of the host immune response . However, the pathogenesis of HP is incompletely understood, and emphasis on environmental control remains the cornerstone of therapy . The prevention, treatment, and prognosis of HP will be reviewed here. The diagnosis of HP is reviewed separately. (See "Diagnosis of hypersensitivity pneumonitis (extrinsic allergic alveolitis)".)
The incidence of HP can be reduced by diminishing exposure to provocative antigens. This may be accomplished by minimizing contact with potential inciting agents, reducing microbial contamination of the work or home environment, or using protective equipment.
Reduction of antigenic burden — Alteration in the handling and storage of potential sources of microbial antigens can diminish the occurrence of HP. As examples, dispersion of actinomycetes spores is decreased by wetting compost prior to handling, and use of antimicrobial solutions in sugar cane processing diminishes fungal growth and the development of bagassosis.
Design of facilities — Indoor microbial contamination is usually related to problems with moisture control . Appropriate design of facilities may reduce stagnant water that is prone to microbial overgrowth. Thus, humidity in occupied buildings should be maintained below 60 percent, carpeting should be avoided in areas where persistent moisture is likely to be present, and water in heating, ventilating, and air conditioning systems should not be recirculated.