There are limited studies. In patients with nonfibrotic HP, avoidance of the causative agent will result in a good prognosis. In patients with fibrotic HP, the prognosis depends not only on avoidance but also on the lung function at diagnosis and the amount of fibrosis that has already occurred. If there is significant fibrosis, it is unlikely that pulmonary function tests will normalize. Other features associated with poor prognosis include cigarette smoking, lower baseline vital capacity, lack of bronchoalveolar lavage lymphocytosis, persistent exposure to the causative antigen, and/or inability to identify a causative antigen.[59]Fernández Pérez ER, Swigris JJ, Forssén AV, et al. Identifying an inciting antigen is associated with improved survival in patients with chronic hypersensitivity pneumonitis. Chest. 2013 Nov;144(5):1644-51.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4694094
http://www.ncbi.nlm.nih.gov/pubmed/23828161?tool=bestpractice.com
[60]Wang P, Jones KD, Urisman A, et al. Pathologic findings and prognosis in a large prospective cohort of chronic hypersensitivity pneumonitis. Chest. 2017 Sep;152(3):502-9.
http://www.ncbi.nlm.nih.gov/pubmed/28223152?tool=bestpractice.com
[61]Ohtsuka Y, Munakata M, Tanimura K, et al. Smoking promotes insidious and chronic farmer's lung disease, and deteriorates the clinical outcome. Intern Med. 1995 Oct;34(10):966-71.
https://www.jstage.jst.go.jp/article/internalmedicine1992/34/10/34_10_966/_pdf/-char/en
http://www.ncbi.nlm.nih.gov/pubmed/8563097?tool=bestpractice.com
[62]Vourlekis JS, Schwarz MI, Cherniack RM, et al. The effect of pulmonary fibrosis on survival in patients with hypersensitivity pneumonitis. Am J Med. 2004 May 15;116(10):662-8.
http://www.ncbi.nlm.nih.gov/pubmed/15121492?tool=bestpractice.com
In the absence of antigen avoidance, deaths have been reported in individuals diagnosed with farmer's lung and pigeon breeder's disease.