Microbiological Safety and Environmental Efficacy of Disposable Bedside Cool-Mist Humidifiers
Bedside room humidifiers can harbor pathogens, and have been linked to nosocomial outbreaks. Our hospital policy requires humidifiers to be filled only with sterile water and discarded after 3 days. This study explores potential risks and benefits of humidifiers when adhering to the policy.
Cool Mist humidifiers (Kaz 4100) filled with sterile water were placed in an empty patient room for 5 days. Daily humidity and temperature readings were obtained from a sensor on the bed (1 meter from the humidifier, within the vapor vector). The experiment was duplicated 22 times: 15 using humidifiers and 7 control runs with no humidifier. The reservoir was sampled daily; 0.5 mL of water was inoculated onto blood agar plates (TSA with sheep blood) and incubated for 7 days at room temperature. On days 3-5, blood agar settle plates were placed at 1, 3, and 5 meters from the humidifier within the vapor vector. Plates were exposed for 1, 5, and 10 minutes at each distance. Statistical analysis was performed with SAS.
We found a significant difference between humidifier and control experiments in both room humidity (38% and 25%, respectively, p<0.001) and temperature (75.2°F and 73.9°F, respectively, p=0.003). There were also significant differences between summer and fall/winter humidity and temperature readings (p<0.001). When controlling for season, the humidifier effect on temperature disappeared, but the effect on humidity remained significant (p=0.006). In multivariable analysis, a higher number of colonies grew from reservoir cultures and settle plates in summer than in fall/winter (p=0.002). Contamination appeared as early as day 1, increased with experiment day (p=0.003), and accelerated after day 3. Settle plate colony count diminished with increasing distance from the humidifier (p<0.001). Further controlling for temperature and humidity did not affect these results. Organisms that grew included skin flora and molds.
Humidifiers had a modest effect on room humidity, but became contaminated over time despite the use of sterile water. Contamination with potential pathogens spread in vapor may pose a risk to immunosuppressed patients, particularly during the summer. This risk is only partially mitigated by replacing humidifiers after three days.
B. K. Decker,
N. Sinaii, None
T. N. Palmore, None