Environmentally mediated disorders of the respiratory tract.
Although much of the evidence in environmental lung disease remains equivocal, some environmental exposures are known to be clinically relevant. Ambient air pollution remains of concern as a source of morbidity, particularly for susceptible populations such as persons with asthma, chronic obstructive pulmonary disease, or cardiac disease and the elderly. The adverse effects of several components of indoor air pollution have been established. Environmental tobacco smoke contributes to lower-respiratory illness in infants; office workers exposed to thermophilic actinomycetes contaminating ventilation systems have developed hypersensitivity pneumonitis; and in the home, components of house dust and fungus spores may provoke asthma via immediate hypersensitivity. The evidence is less compelling for a link between other exposures and disorders of the respiratory tract. For example, formaldehyde may be responsible for provoking vague respiratory symptoms and even nasal cancers; however, the associations are unproved. Likewise, the relation between low-level exposure to asbestos and the development of lung cancer, although a concern, is not conclusively established. The clinician should be aware of practical measures for patients who inquire about air cleaning. Often, relatively simple solutions are effective. A knowledge of sources and exposures as well as an understanding of the principles of inhalation lung injury should prove useful in directing patient care.