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UVC disinfection of MDR pathogens

UVC disinfection of MDR pathogens

Published Mar. 29, 2021
Hospital settings harbour several multidrug-resistant pathogens. These stubborn organisms increase morbidity, mortality and health-care costs significantly. Cleaning and disinfection are particularly important in hospitals where the proportion of vulnerable individuals is much higher than in any other environment. Believe it or not, microorganisms are extremely resilient and manage to survive on inanimate objects/surfaces for several days.

Traditional manual methods of cleaning and disinfection are not completely effective in eradicating these pathogens. Different assessment tools such as visual observation, adenosine triphosphate bioluminescence, aerobic colony counts point to the same conclusion. 

Thus, in addition to manual cleaning, a no-touch method can help improve terminal room disinfection. UV-C technology is the most intensely studied alternative to conventional disinfection procedures in hospitals. At 254nm UV-C radiation can damage DNA by inducing formation of pyrimidine dimers. DNA damage can reduce the replicative ability of microorganisms severely. Use of UV-C devices offers distinct advantages over standard disinfection methods:

  • Germicidal action against broad-spectrum of organisms
  • Safe and eco-friendly with little or no hazardous waste production
  • Shorter time for inactivation of vegetative bacteria
  • Easy to set up and operate in healthcare settings
  • Saves labour and consumables

Certain areas are frequently missed by cleaning staff or remain contaminated even after cleaning, such as edges of tables, corners and crevices. A UV-C lamp may provide a uniform coverage for these problem areas

This study, which was conducted at a 2400-bed acute care medical center at National Taiwan University Hospital, assessed the reduction in frequently encountered MDR clinical isolates, namely P.aeruginosa (MDRPA), Acinetobacter baumannii (MDRAB), MRSA, VRE, Mycobacterium abscessus and Aspergillus fumigatus due to UVC exposure. 

The in-vitro study involved growing stored clinical strains of P. aeruginosa (MDRPA), multidrug-resistant A. baumannii (MDRAB), VRE, methicillin-resistant S.aureus (MRSA, ATCC 33592), and M. abscessus (ATCC 19977) on solid media. A. fumigatus (ATCC 204305) fungal spores were cultured in suspension for all experiments.

The multi-motion sensor enabled UV-C device was calibrated to deliver a dose of 2750 mW/cm2 at a distance of 1m, 2m and 3m from the table where the experimental petri-dishes were placed. A single petri-dish was tested in each irradiation cycle. The duration of the irradiation was also varied: 5, 10 and 15 minutes of exposure.  The effectiveness of UV-C disinfection on environmental surfaces in 3 patient rooms was assessed by placing the UV-C robot in 3 different locations in each room. The rooms were previously occupied by patients with MRSA, VRE and other nosocomial pathogens with at least 7 days of hospitalization. Swabs moistened with saline were used to collect cultures from 20 high-touch surfaces in these rooms before and after UV-C exposure. 

The killing efficacy of UV-C radiations was inversely proportional to the distance of the petri dishes from the lamp and directly proportional to the exposure time. At 1m distance, all strains of tested bacteria displayed comparable reduction irrespective of exposure time. Under the most stringent condition, (5-minute exposure at a distance of 3 meters) UV-C could eliminate more than 3 log10 vegetative bacteria, except for VRE and M. abscessus which decreased to 1.5-2.5 log10 CFU. The fungus A.fumigatus was resistant to UV-C at a distance of 2-3 meters. 

Of the twenty high-touch surfaces sampled, except for bed rail, bedside table and telephone, all surfaces showed a 100% reduction in total bacterial colony count after UV-C irradiation. 15 minutes of exposure seemed to be optimum for significant reduction of bacterial colony count after 24h and 48 h of incubation. 

The highlight of this study is the testing of vulnerability of nontuberculous mycobacteria (NTM) and Aspergillus to UV-C in experimental setting. NTM causes skin and soft tissue infections, surgical site infections, and iatrogenic bloodstream infections. Invasive fungal infections caused by Aspergillus is very common healthcare settings and immunocompromised patients. Successful reduction of these organisms by more than 3 log10/cm2 by 5-15 minutes of UV-C exposure at a distance of 1m suggests that strategic placement of UV-C devices in hospital rooms can be very helpful in controlling these nosocomial infections

Despite all the attractive benefits of UV-C disinfection, it should be used as a supplement to manual cleaning because the distance of the irradiated surface from the lamp is important. UV-C cannot be used in crowded areas; shadowed surfaces are not adequately irradiated with UV-rays and certain high-touch surfaces require frequent manual cleaning for optimum disinfection. 

Yang, J.-H., Wu, U.-I., Tai, H.-M., & Sheng, W.-H. (2019). Effectiveness of an ultraviolet-C disinfection system for reduction of healthcare-associated pathogens. Journal of Microbiology, Immunology and Infection, 52(3), 487–493. doi: 10.1016/j.jmii.2017.08.017

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