An outbreak of hypersensitivity pneumonitis at a metalworking plant: a longitudinal assessment of intervention effectiveness.

The authors describe a longitudinal assessment of intervention effectiveness in response to an outbreak of hypersensitivity pneumonitis (HP) at a metalworking facility. Thirty-five (29%) of the plant's 120 production workers were given a clinical diagnosis of HP during the two years of the investigation. Although quantitative exposure assessment tools were of limited utility, the investigators successfully used qualitative observations and the patients' return-to-work experiences to iteratively evaluate their exposure control recommendations. Recommended interventions included improving metalworking fluid management practices, enclosing selected metalworking fluid machining operations, eliminating mist cooling, exhausting two additional water-based industrial processes, increasing general dilution ventilation, and worker training. As of November 1999, 26 months into the outbreak, 51 percent (18) of the employees with a clinical diagnosis of hypersensitivity pneumonitis had been able to return to work. The symptom onset of the 35 workers who were given a clinical diagnosis of hypersensitivity pneumonitis during the two-year study period predated the implementation of the interventions. The collaboration of a multidisciplinary team appears to have allowed for successful intervention in this setting. A specific etiological agent(s) associated with the outbreak was not confirmed during the investigation. An acid fast isolate identified as being in the Mycobacterium chelonae group was detected in only one of the submitted metalworking fluid (MWF) sump samples. Longitudinally, there was a statistically significant difference in MWF sump bacteria (X(2) = 286.4, df = 17, p <.0001) and MWF sump fungi (X(2) = 28.1, df = 7, p <.0002). Measured oil mist air levels did not exceed the Occupational Safety and Health Administration's (OSHA's) permissible exposure limit (PEL), and in fact, did not exceed 0.5 mg/m(3).