The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

ULTRASONIC VS. ULTRAVIOLET: WHICH PRODUCES FEWER BACTERIA?

Deborah Cullen, Ed, RRT, FAARC, Sarah Vinson, BS, CRT, Danielle Kerr, BS, CRT, Kelly Miller, BS, CRT, Linda Marler, MS, MT(ASCP)SM Indiana University, Indianapolis, IN

Background: Home humidifiers can provide beneficial moisture to the air and their patients, but can also become harmful when they spread bacteria that can lead to infection. The purpose of our research was to determine which room humidifier, the ultraviolet or ultrasonic, promotes the growth of fewer microorganisms and therefore would be more hygienic for home use. The ultrasonic humidifier creates a cool mist by means of ultrasonic sound vibrations. The ultraviolet humidifier uses the germicidal power of ultraviolet light to provide humidification.

Method: Six humidifiers, three ultrasonic humidifiers and three ultraviolet humidifiers were utilized. Our controls for this evaluation were one of the ultrasonic humidifiers and one of the ultraviolet humidifiers. These two humidifiers were filled with tap water but not run. The remaining four humidifiers were filled, when necessary, with tap water from the same source and run continuously Monday through Friday for two weeks to simulate home use. We measured bacterial counts in the humidifiers using sterile technique, on days 1 (before units were turned on), 3, 5, 8, 10, and 12. Each 1 ml sample was plated on 5% Trypticase Soy Agar with 5% Sheep Blood (BAP), incubated at 37oC in an ambient air incubator, and examined for growth each day for 5 days. Colonies were counted on each plate and identified by a clinical microbiologist using standard practices (growth on various media, Gram stain, and biochemical tests) used in the clinical laboratory for the identification of routine bacterial and fungal isolates. It was beyond the scope of this study to use special culture procedures to isolate fastidious organisms.

Results:
Colony counts (per 1 ml) were as follows:

Day 1 Day 3 Day 5 Day 8 Day 10 Day 12

UV-1 1/ml 0 1 0 0 0

UV-2 0 0 0 0 0 0

UV-3 0 0 0 0 0 2

US-1 58 44 49 96 71 >100

US-2 25 8 2 >100 >100 >100

US-3 8 1 7 18 25 >100

Experience: The ultrasonic humidifier permitted bacterial growth as compared to the ultraviolet humidifiers. The ultraviolet humidifiers limited 99% of bacteria growth, but on average cost about $50-70 more than the ultrasonic humidifiers. Respiratory therapists should consider recommending ultraviolet humidifiers, when appropriate, to patients and their families. Conclusion: Ultrasonic humidifiers were highly populated with bacteria in the control as well as the two other units from Day 1 through Day 12. All ultrasonic humidifiers tested were harboring bacteria even when just opened from the box. The ultraviolet humidifiers had little to no bacterial growth.

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