The presence of humidifier disease in a printing factory was investigated with particular emphasis on airborne endotoxins. The water in the humidifier was contaminated with Pseudomonas. The amount of airborne endotoxin when the humidifier was operating was 0.13-0.39 μg/m3. Twenty of the fifty workers investigated reported typical symptoms of fever, chills, and chest tightness when the humidifiers were operating. Symptoms were more frequent among non-smokers.
The estimated inhaled dose of endotoxin was found to be sufficient to cause the observed symptoms. The determination of airborne endotoxins in future episodes of humidifier disease is recommended.