Aerosol mapping of a facility with multiple cases of hypersensitivity pneumonitis: demonstration of mist reduction and a possible dose/response relationship.

Recent outbreaks of hypersensitivity pneumonitis (HP) have been associated with exposures to metalworking (MWF) fluid aerosols. Mycobacteria present in mismanaged fluids have been suggested as the likely culprit. In January 2001, three machinists at a machining plant were hospitalized with HP. Subsequently, additional HP cases developed as well as cases of bronchitis and occupational asthma. In October 2001, an aerosol concentration map was constructed to advise on priorities for corrective actions. In April 2002 after installation of mist collectors, a second map was generated. Mist reductions varied from about 75 percent to an increase of about 20 percent. Mist concentrations increased in the areas near an uncontrolled transfer line. Subsequent to the first mapping exercise, the exposures of 30 HP cases were classified as low, medium, and high based on job location and the map. There were 6 cases among low exposure jobs (4% of exposed), 14 cases among medium exposure jobs (19% of exposed), and 10 cases among high exposure jobs (34% of exposed), suggesting a relation between exposure to contaminated metalworking fluid mist and the development of HP. A combination of interventions (fluid management, mist control, improved fresh air ventilation, and medical surveillance/restriction) eliminated any new cases 11 months after the first diagnosis of HP.