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Global Health Technologies

Undergraduate Lightning Talks

UVC Disinfection of a Low-Cost Bubble CPAP

Saturday, October 26, 2024
1:10 PM – 1:15 PM EST
Location: Room 342

Introduction:  Bubble continuous positive airway pressure (bCPAP) devices provide respiratory support to preterm infants to allow spontaneous breathing. However, many current bCPAP devices are expensive and unaffordable for low to middle income countries [1]. Therefore, there is a need for a low cost bCPAP device designed to be cost effective without compromising safety, effectiveness, or reliability. Therapeutic Innovations is working to fill this need with the AirBaby. Bubble CPAP devices like the AirBaby work by providing a heated, humidified air and oxygen blend using a humidifier water chamber. If non-sterile water is added to the humidifier chamber, the warm temperatures promote bacterial growth. Because the AirBaby humidifier is designed to be manually refilled and limited-resource hospitals may not have access to clean water, providing a way to disinfect the humidifier water while the device is running could help prevent infection and make the device safer for patients. Shortwave ultraviolet (UVC) light can be used for disinfection because it breaks the DNA and RNA strands of bacteria and viruses, preventing reproduction [2]. Many bulb-based UVC lights are used for disinfection in hospitals and other household devices. However, UVC LEDs provide an alternative for UVC light on a much smaller scale. This project investigated the intensity and bacterial disinfection capabilities of a UVC LED to determine the efficacy of integrating UVC light into the AirBaby’s humidifier chamber.

Materials and

Methods:  To measure UVC intensity at different power levels and distances, a UVC LED was positioned 5 - 75 mm from a UVC meter and powered at 0.13 - 0.43W by limiting current and voltage. Once stable, intensity was recorded for each position. To verify the relationship between power and intensity, the LED was positioned 20 mm from the meter and power was adjusted from 0.05 to 0.4W. This procedure was repeated 3 times with 5 minutes of no power between trials.

To assess bacterial disinfection by UVC light, 1.876mL of E. coli OP50 stock was added to 500mL of sterilized tap water and stirred at 330 rpm. After one minute, a 100uL control sample was collected on an agar plate. The 500mL solution was exposed to UVC light at 0.05 - 0.2W for 40 minutes, then a 100uL sample was collected. Plates were incubated at 37℃ for 48 hours then observed for bacterial colony formation.

To assess disinfection by long UVC exposure, a humidifier filled with 500mL non-sterile tap water was connected to an air pump. After one minute of 4 L/min airflow, a 0.6 mL sample was collected on an agar plate. Then, the UVC LED was powered continuously at 0.28 - 0.3W or programmed to shine for 15 minutes per hour (25% duty cycle). Water samples were collected on agar plates at 2, 4, 6, and 24 hours of UVC exposure. After incubation at 37℃ for 2 - 3 days, bacterial colonies were counted.

Results, Conclusions, and Discussions: UVC light intensity exponentially decreased with distance to the UVC LED regardless of power level, supporting the inverse square law. As power increased, UVC LED light intensity plateaued beginning at 0.2W. The iClevr Sanitizing Wand, a bulb-based UVC light marketed for household disinfection, has an intensity approximately 45x greater than a single UVC LED. A similar bulb-based UVC light used in hospitals has a reported disinfection time of 5 minutes [3]. Therefore, a single UVC LED would require approximately 4 hours to deliver the same dose of irradiation as its larger, bulb-based counterparts. However, disinfecting a liquid volume may impact the irradiation dose required compared to a rigid surface. When exposing E. coli in liquid to UVC, the number of visible colonies present after 40 minutes decreased in a dose dependent manner. Furthermore, continuously exposing the water in the AirBaby’s humidifier chamber to UVC reduced bacterial counts to zero by 24 hours exposure. Exposing the humidifier water to 15 minutes of UVC every hour also reduced the number of bacteria present at a slower rate, likely because any remaining bacteria is able to reproduce when the light is off. Ultimately, these results suggest that continuous, low-power UVC LED exposure of the CPAP humidifier chamber is effective in reducing bacterial growth. Further studies of other common, waterborne infectious organisms and viruses would help identify the full impact of exposing UVC light into the CPAP humidifier chamber.

Acknowledgements (Optional):  [1] Kamath, Beena D., et al. “Neonatal Mortality From Respiratory Distress Syndrome: Lessons for Low-Resource Countries.” Pediatrics, vol. 127, no. 6, June 2011, pp. 1139–1146, https://doi.org/10.1542/peds.2010-3212.

[2] Ruiz-Díez, Carlos, et al. “Optimization of UV-C pulsed radiation strategy for a high-efficiency portable water sterilizer.” Environmental Technology & Innovation, vol. 31, Aug. 2023, https://doi.org/10.1016/j.eti.2023.103199.

[3] “Optimum-UV Clinical & Laboratory Evidence.” Clorox Healthcare, 2018.

Special thanks to Elizabeth Fio, Julian Schneider, and Stephen Larson for their introduction to working with the AirBaby and aseptic lab techniques. This work was supported by NSF REU grant EEC2150076.