High index of suspicion of disease when evaluating individuals with interstitial lung disease or recurrent flu-like illness.
History of exposure to organic dust: for example, birds, agricultural dusts, and moulds.
Immunological reaction to inhaled antigen is corroborative.
No pathognomonic tests.
Treatment involves avoidance of causative agent and use of corticosteroids.
Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, is the result of non-IgE mediated immunological inflammation. HP is caused by repeated inhalation of non-human protein, which can be of natural plant or animal origin or can be the result of a chemical conjugated to a human airway protein, such as albumin. The inflammation of HP manifests itself in the alveoli and distal bronchioles. The clinical manifestations of HP depend on the concentration and frequency of exposure. The clinical syndromes - acute, sub-acute, and chronic HP - present differently.   Some authors are now reporting that there are only two clinical syndromes; however, they vary as to whether they group sub-acute with the acute or the chronic form.   Many cases of HP are caused by occupational exposure. 
Northwestern University Feinberg School of Medicine
Ernest S. Bazley Asthma and Allergy Center
Clinic Practice Director
Northwestern Medical Faculty Foundation
LG declares that she has no competing interests.
Professor of Pediatrics
Medical College of Wisconsin
JF is an author of a number of references cited in this monograph.
Professor of Family Medicine
Medical University of South Carolina
AC declares that he has no competing interests.
Consultant Respiratory Physician
Interstitial Lung Disease Unit
Royal Brompton Hospital
TMM has received consultancy fees from GSK, Actelion, and Philips Respironics. He has received lecture fees from Astra Zeneca and holds an unrestricted industry-academic grant from GSK.
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