Hypersensitivity pneumonitis is a form of interstitial lung disease caused by a wide array of
respirable particles. Given the widespread prevalence of many implicated exposures, contributing
factors such as genetic predisposition and concomitant environmental factors likely influence the risk
of disease development. Common causes include a range of bacterial and fungal species, and a number
of chemical exposures such as to isocyanates. Exposures to microbial contaminants can occur in a
range of domestic, recreational and occupational settings. Occupational exposures to microbial
contamination include and are not limited to the farming industry, the manufacturing industry which
frequently requires the use of metalworking fluids, and the food industry. Diagnostic assessment initially relies on a high
index of clinical suspicion. Subsequent workup integrates clinical history, pulmonary function testing and radiologic
imaging with a high resolution chest CT scan. In certain clinical scenarios, serological testing, bronchoscopy with
bronchoalveolar lavage and/or surgical lung biopsy may be informative.
Keywords: Hypersensitivity pneumonitis, extrinsic allergic alveolitis, interstitial dung disease, farmer’s lung, hot tub lung,
summer-type hypersensitivity pneumonitis, isocyanates, specific inhalation challenge testing.
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