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Effective disinfection of contaminated surfaces is essential to prevent the spread of hospital pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile.

Efforts to improve disinfection are mainly manifested in the high-frequency contact surface of the ward. However, there is evidence that portable devices and other shared devices may also be a way for pathogens to spread. Mobile communication equipment is one of the most commonly used equipment in hospitals. Studies have shown that in a clinical environment, mobile phones may be contaminated by microbiota and hospital pathogens carried by users.

Recently, more and more medical institutions have begun to use ultraviolet (UV) disinfection systems to limit the spread of pathogens in hospitals and prevent infections related to healthcare. The most widely used ultraviolet disinfection system includes 254nm ultraviolet C (UVC) germicidal lamps. Because 254nm UVC can cause damage to the skin and eyes, the UV disinfection system is mainly used in open spaces. Previous reports have shown that UVC rays with a wavelength of 222nm are part of the far UVC spectrum (207-222nm) and have high-efficiency bactericidal properties. Compared with UVC with a wavelength of 254nm, it is safer for human eyes and skin. However, there are few reports on the disinfection effect of 222nm UVC in the clinical environment. In this study, the degree of MRSA contamination on mobile phones used by doctors in hospitals and the disinfection effect of 222nm UVC on these devices were investigated.

From March 2020 to May 2020, in Hiroshima University’s 746-bed third-class hospital in Hiroshima, Japan, 50 doctors’ mobile phones dedicated to hospital use were sampled for bacterial contamination. A 25 cm2 tryptone soy agar (TSA, containing lecithin and polysorbate) was used for sampling on a RODAC plate (25 cm2; Nippon Becton Dickinson Co., Ltd., Tokyo, Japan). When sampling, press the RODAC tablet tightly on the surface of the phone keys for at least 10 seconds.

After sampling, the contact plate was immediately sent to the clinical laboratory of Hiroshima University Hospital and incubated at 37°C under aerobic conditions for 48 hours. After counting the plates, estimate the total number of colony forming units (CFU) of all aerobic bacteria (AB) in each sample. MRSA colonies were identified based on the unique color and morphology of the colonies on the plate and the results of the Staphylococcus aureus selective latex agglutination test (PS Latex; Eiken Chemical Co, Tokyo, Japan). Then it was subcultured and identified using standard microbiological methods, and the CFU count of MRSA in each sample was estimated.

In order to evaluate the actual efficacy of Far UVC 222, 50 doctors’ dedicated hospital mobile phones were sampled and cultured before and after 222nm UVC disinfection (each mobile phone was exposed to UV for 1.5 minutes). 25 mobile phones sampled the back side before disinfection, and sampled the front buttons after 222nm UVC disinfection. For the remaining 25 mobile phones, the front buttons were sampled before disinfection, and the back was sampled after 222nm UVC disinfection. When sampling, press the RODAC tablet tightly on the surface or back of the phone buttons for at least 10 seconds. After sampling, the plates were incubated aerobically at 37°C for 48 hours, and then the number of ABCFU on each plate was counted.

Of the 50 mobile phones, 5 (10%) were contaminated by MRSA. The median of ABCFU was 17 (range: 3-122), and the mean±standard deviation of AB CFU was 25.2±24.5. For MRSA-positive samples, the median MRSACFU was 3.5 (range: 0-6), and the mean±standard deviation of MRSACFU was 3.4±1.7. The average reduction of log10MRSA CFU on the mobile phone panel is shown in Table 1. The mean±standard deviation of MRSA CFU of the control plate was (9.43±0.98)×106. 222nm UVC irradiation for 1.5 and 2.5 minutes (9 and 15mJ/cm2) can reduce log10MRSA CFU by 2.91 and 3.95 on average, respectively. The number of Log10MRSA CFU decreases with the prolongation of the irradiation time.

Table 2 summarizes the effectiveness of 222nm ultraviolet disinfection in reducing AB pollution on mobile phones dedicated to doctors in hospitals. Before disinfection, there was no significant difference in the number of front buttons and back CFU between the two groups (P=0.7). However, after 9mJ/cm2 of 222nm UVC irradiation (0.1mW/cm2, 1.5 minutes), the AB pollution on the two groups of mobile phones was significantly reduced. Compared with the baseline, 222nm UVC irradiation reduced AB pollution by 93.4% and 94.7%, respectively.

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Post time: Apr-25-2021