Bacterial output from three respiratory therapy humidifying devices

Three devices used to humidify the air delivered to hospitalized patients were evaluated for their relative hazard as measured by the concentration of bacterial output delivered with the gas. Two of the devices were evaporative types (commonly called "humidifiers"), moisturizing with water vapor, while the third was a nebulizer, delivering water droplets in aerosol form. Reservoirs were seeded with a tracer organism Pseudomonas cepacia (approximately 10(4)/ml) in distilled water. The output gas (approximately 30 1/min) was sampled through an Andersen six-stage bacterial sampler operated at 28.3 1/min. Excess gas was bled off through a Y-tubing. Results indicate that the nebulizer produces heavily contaminated bacterial aerosols (greater than 1000 P cepacia colonies in the 3-minute sampling period) even after a 20-minute warm-up period that raised the reservoir temperature to greater than 45 degrees C. The two evaporative type devices produced virtually no viable organisms even when sampling was initiated with the reservoir at room temperature.