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Updated: Oct 24, 2025
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Published on: May 7, 2013
A cluster of hypersensitivity pneumonitis associated with exposure to metalworking fluids
Aaron W Tustin1, Ryan Cooney2, Glenn E Lamson3
1Office of Occupational Medicine and Nursing, Directorate of Technical Support and Emergency Management, Occupational Safety and Health Administration, Washington, District of Columbia, USA.
Background:
Workers exposed to metalworking fluids (MWF) can develop respiratory illnesses including hypersensitivity pneumonitis (HP). These respiratory manifestations are likely due to microbial contamination of aerosolized MWF. This paper reports a cluster of HP and respiratory symptoms at a manufacturing plant where MWF and workplace air were contaminated with bacterial endotoxin despite frequent negative bacterial cultures of MWF.
Methods:
A pulmonologist assessed and treated three workers with respiratory symptoms. The Occupational Safety and Health Administration (OSHA) inspected the plant. OSHA's investigation included bacterial culture of MWF, measurement of endotoxin concentrations in MWF and workplace air, review of the employer's fluid management program, and distribution of a cross-sectional symptom questionnaire.
Results:
Three workers had biopsy-confirmed HP. In addition, 30.8% of questionnaire respondents reported work-related respiratory symptoms. OSHA detected endotoxin levels as high as 92,000 endotoxin units (EU)/ml in MWF and 3200 EU/m3 in air. Endotoxin concentrations and risk of MWF inhalation were highest near an unenclosed multistation computer numerical control machine. A contractor had tested this machine's MWF for bacterial growth weekly during the preceding three years, and most (96.0%) of those tests were negative.
Conclusions:
Contaminated MWF can cause severe occupational lung disease even if microorganisms do not grow in fluid cultures. Endotoxin testing can increase the sensitivity of detection of microbial contamination. However, employers should not rely solely upon MWF testing data to protect workers. Medical surveillance and meticulous source control, such as engineering controls to suppress MWF mist and prevent its inhalation, can reduce the likelihood of respiratory disease.
Insights
Workers exposed to metalworking fluids (MWF) can develop hypersensitivity pneumonitis (HP) due to endotoxin contamination, even with negative bacterial cultures. Monitoring endotoxin levels and implementing engineering controls are crucial for preventing occupational lung disease.
Area of Science:
- Occupational Health
- Environmental Science
- Pulmonology
Background:
- Metalworking fluids (MWF) aerosols can cause respiratory illnesses like hypersensitivity pneumonitis (HP).
- Microbial contamination of MWF is a suspected cause of HP in exposed workers.
- A cluster of HP and respiratory symptoms occurred at a plant with endotoxin-contaminated MWF and air, despite negative bacterial cultures.
Purpose of the Study:
- Investigate a cluster of hypersensitivity pneumonitis (HP) and respiratory symptoms in workers exposed to metalworking fluids (MWF).
- Assess MWF and workplace air for microbial contamination, specifically bacterial endotoxin.
- Evaluate the effectiveness of the employer's fluid management program and identify risk factors.
Main Methods:
- Clinical assessment and treatment of symptomatic workers by a pulmonologist.
- Inspection by the Occupational Safety and Health Administration (OSHA), including MWF bacterial cultures and endotoxin measurements.
- Distribution of a cross-sectional questionnaire to assess work-related respiratory symptoms.
Main Results:
- Three workers were diagnosed with biopsy-confirmed HP.
- 30.8% of questionnaire respondents reported work-related respiratory symptoms.
- High endotoxin levels were detected in MWF (up to 92,000 EU/ml) and air (up to 3200 EU/m³), with highest risks near unenclosed machinery.
Conclusions:
- Contaminated MWF can cause severe lung disease, detectable by endotoxin testing even with negative bacterial cultures.
- Employers must not rely solely on bacterial cultures for MWF safety.
- Medical surveillance and engineering controls to minimize MWF mist inhalation are essential for preventing occupational respiratory disease.
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