Interstitial Pneumonitis Due to Hypersensitivity to an Organism Contaminating a Heating System

Intermittent cough and dyspnea, associated with pulmonary function abnormalities of restriction and a diffusion defect, and an interstitial granulomatous pneumonitis without an overt cause developed in a middle-aged housewife. Her symptoms appeared during the heating season, and she became asymptomatic when away from home. Because of this association of symptoms with her home environment, a bacteriologic and immunologic investigation of her residence was carried out. A thermophilic actinomycete resembling Micropolyspora faeni, known to cause the hypersensitivity pneumonitis farmer's lung, was repeatedly isolated from the furnace humidifier. Precipitins against this organism were detected in her serum, and all symptoms of her disease could be reproduced by a controlled inhalation exposure to an extract of the organism. Removal of the forced-air furnace resulted in a remission of her illness. These findings suggest that a thorough environmental search should be carried out in all cases of so-called "idiopathic" interstitial pulmonary disease.