Mycobacterium sp. as a Possible Cause of Hypersensitivity Pneumonitis in Machine Workers

Interest in occupational hypersensitivity pneumonitis (HP) or extrinsic allergic alveolitis is increasing (1,2). HP, a rare group of diseases characterized by recurrent dyspnea, cough, and systemic signs such as myalgia and fever, is caused by repeated exposure and subsequent sensitization to various antigens. Recognized antigens are often fungal or bacterial. The disease process is thought to involve lymphocytesensitization and cell-mediated immune response that ultimately results in alveolitis. Types of occupational HP include farmer’s lung, bird fancier’s lung, and mushroom worker’s lung. HP has recently been recognized among metal workers, and as evidenced at a recent meeting of the Automotive Manufacturers Association in Detroit (September 1997), controversy exists as to its possible cause(s). Researchers from the National Institute for Occupational Safety and Health recently reported that four of six outbreaks of HP in metal-working facilities yielded unusual flora (e.g., Mycobacterium chelonae) in contaminated MRFs (2,3). They discussed acid-fast bacteria, nontuberculous mycobacteria, gram-positive bacteria, and fungi as possible causes (3) but more recently concluded that the specific etiologic agent(s) for HP among workers exposed to (MRF) aerosol remain(s) unknown (2). Advances in metal removal fluid technology have led to the use of synthetic, semisynthetic, and soluble fluids, as opposed to traditional oil coolants. These water-based coolants are typically recycled and often become colonized by microorganisms. We present case reports and observations that further suggest mycobacteria may be a cause of occupational HP.