Brooke K. Decker MD, Roshni Patel, Ninet Sinaii, Ph.D

1370!
Microbiological Safety and Environmental Efficacy of Disposable
Bedside Cool-Mist Humidifiers!
Brooke K. Decker
1Hospital
1,2,3
M.D.,
Roshni
1
Patel,
Ninet Sinaii, Ph.D,
!
4
M.P.H.,
Tara N. Palmore,
Methods
!
!
We filled Cool Mist humidifiers (Kaz 4100) with sterile water and placed them in an empty patient room. Each humidifier was run 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 and included repeated measures analysis using mixed modeling. !
The humidification of dry air, especially in the winter, may be soothing to
chapped nasal and bronchial mucus membranes. However, humidifiers have
long been associated with human illness. “Monday Fever,” a respiratory
condition more pronounced after tolerance to the causative workplace
system is lost over the weekend, was described some 37 years ago.
Numerous reports since then have implicated humidifiers in allergic
syndromes and transmission of pathogens.!
!
Hospital bedside room humidifiers are difficult to sterilize and provide a
sanctuary for waterborne organisms. They can harbor pathogens such as
Acinetobacter, Pseudomonas, and Burkholderia species. Humidifiers can
aerosolize bacteria, and have been linked to nosocomial outbreaks. The
appropriateness of providing bedside humidifiers to hospitalized patients has
been debated.!
!
At the NIH Clinical Center, a 240-bed clinical research hospital, policy allows
patients to request bedside humidifiers, but stipulates that the humidifiers
must be filled with sterile water and the humidifier must be discarded after 3
days of use. This study explores potential risks and benefits of humidifiers
when adhering to our policy. !
5 meters!
3 meters!
Settling plates!
1 meter!
!
Organism growth from humidifier cultures Organisms grown on se<ling plates Data from humidifier rooms, by season 0 8 2 P < 0.01!
2 1 1 Summer MEAN 5 Fall/Winter MEAN Figure 1: The number of colonies isolated by distance from
the humidifier. Distance “0” is the humidifier reservoir itself.
There was a significant difference between summer and fall/
winter colony numbers overall and by distance.!
Bedside patient humidifiers had a modest effect on room humidity,
but became contaminated with bacteria and mold over time despite
the use of sterile water and only once-daily refilling. This risk is only
partially mitigated by replacing humidifiers after three days.!
!
The bacteria identified were common environmental molds as well
as skin flora (see table) that most likely came from the investigators.
It seems likely that patients who are colonized with multidrugresistant organisms may likewise contaminate their environment
(including humidifier) with potentially pathogenic organisms. !
!
The aerosolization of these pathogens in humidifier vapor may pose
an inhalation risk, especially to immunosuppressed patients, or
patients susceptible to lung infections. Interestingly, our study
showed an increased positivity of settling plates during the summer,
however, it is not possible to determine whether this observation was
due to the humidifier.!
!
Based on the results of our study, we would recommend against the
use of bedside humidifiers in hospitals, particularly those that serve
immunosuppressed patients. Humidification of oxygen lines could be
used as an alternative measure to improve patient comfort.!
6 5 4 3 P = 0.002!
2 !
This research was supported by the National Institutes of Health
Clinical Center and the National Institute of Allergy and Infectious
Diseases. !
!
This work was made possible by the Clinical Center Microbiology
Service. We appreciate the contributions of our colleagues in the
Clinical Center Hospital Epidemiology Service: Angela Michelin,
Amanda Ramsburg, Robin Odom, and MaryAnn Bordner. !
1 0 0 1 3 Distance (m) from humidifier Mold identified:
Aureobasidium pullulans, Basidiomycetes, Cladosporium, Paecilomyces
variotii, Penicillium, Syncephalastrum spp., Yeast
Acknowledgments!
7 Number of colonies Number of colonies Number of colonies 3 1 !
Organism growth from reservoir cultures 3 1 hominis, Staphylococcus warneri, Micrococcus luteus
!
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), but duration of exposure had no effect on either temperature or humidity. 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.!
P = 0.001 by distance!
P < 0.01 between seasons!
identified:
!Bacteria
Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus
Conclusions!
!
2 !Brooke Decker!
!9000 Rockville Pike!
!10/2C145!
!Bethesda, MD 20892!
[email protected]!
!
Results!
3 Correspondence:
!
!
!
!
!
!
!
!
!
Vapor vector!
!
!
!
.
0 !
Epidemiology Service, National Institutes of Health (NIH), Bethesda, MD, 2Critical Care Medicine Department, NIH, 3National Institute
of Allergy and Infectious Diseases, NIH, 4NIH Clinical Center Biostatistics and Clinical Epidemiology Service, NIH!
Background!
2 1,3
M.D.
1 2 3 4 Day of humidifier run Summer MEAN 5 Fall/Winter MEAN Figure 2: The number of organism colonies isolated from the
humidifier by day of sampling. Overall, there was a significant
difference in contamination as time elapsed during both
summer (p<0.01) and fall/winter (p=0.037).!
1 2 Summer MEAN 3 4 Day of humidifier run Fall/Winter MEAN 5 Combined Figure 3: The number of organism colonies isolated per day
from the reservoir only. The differences over time were
significant overall (p=0.002), contributed by day 5 (p=0.01),
but there was no overall seasonal difference (p=0.21).!
References!
!
1.  Babington, D., et. al., Humidifier Fever. Thorax, 1977. 32: p. 653-663 !
2.  Smith PW, M.R., Room humidifiers as the source of Acinetobacter infections. JAMA, 1977. 237(8): p. 795-797. !
3.  Chatburn RL, L.M., Klinger JD, An in-hospital evaluation of the sonic mist ultrasonic room humidifier. Respir Care,
1984. 29(9): p. 893-899.!
4.  Rhame FS, S.A., McComb C, Boyle M, Bubbling humidifiers produce microaerosols which can carry bacteria.
Infect Control, 1986. 7(8): p. 403-7.!
5.  Yiallouros PK, P.T., Karaoli C, Papamichael E, Zeniou M, Pieridou-Bagatzouni D, Papageorgiou GT, Pissarides N,
Harrison TG, Hadjidemetriou A, First outbreak of nosocomial Legionella infection in term neonates caused by a
cold mist ultrasonic humidifier. Clin Infect Dis, 2013. 57(1): p. 48-56.!
6.  Moran-Gilad J, L.T., Mentasti M, Harrison T, Weinberger M, Mordish Y, Mor Z, Stocki T, Anis E, Sadik C, Amitai Z,
Grotto I, Humidifier-associated paediatric Legionnaires' disease, Israel, February 2012. Euro Surveill, 2012.
17(41): p. 20293.!
7.  Gervich DH, G.C., An outbreak of nosocomial Acinetobacter infections from humidifiers. Am J Infect Control,
1985. 13(5): p. 210-215.!
8.  Craig, CP, Room Humidifiers and Hospitals. Infect Control, 1985. 6(3): p. 129-130.!
!
!