HOME HUMIDIFIERS AS A POTENTIAL SOURCE OF EXPOSURE TO MICROBIAL PATHOGENS, ENDOTOXINS, AND ALLERGENS

The propensity of various types of home humidifiers to support and dis seminate microbial contaminants into indoor air was tested. Reservoir water and air discharged from humidifiers seeded in the laboratory or naturally contaminated in the home were analyzed by standard microbiol ogical methods. Clinically insignificant as well as overt or potential ly pathogenic microorganisms were found to colonize the reservoirs of all types of humidifiers, but only cool mist and ultrasonic units read ily aerosolized bacteria and endotoxin. Only cool mist units emitted h ydrophobic fungal spores. Cool mist units discharged the greatest numb er of water particles in the inhalable size range (4-16 mu m) while ul trasonic units were more likely to emit respirable-sized water particl es (< 0.2-4 mu m). Overt pathogens isolated from humidifiers in homes included Legionella and a pathogenic Acanthamoeba. Aerosolizing humidi fiers should thus be avoided if frequent, thorough cleaning of the uni ts is not practical.