Cell phones, a habitual carry-on item, are also polluting the treatment environment. The correct use of the UV lamp is very important!

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

Efforts in disinfection improvement have been primarily on high-frequency contact surfaces inwards. However, there is evidence that portable and other shared devices may also serve as a pathway for pathogen transmission. Mobile communication devices are among the most commonly used devices in hospitals, and studies have shown that in clinical settings, cell phones may be contaminated with microbiota and hospital pathogens carried by users.

Recently, an increasing number of healthcare facilities have begun using ultraviolet (UV) disinfection systems to limit the spread of hospital pathogens and prevent healthcare-associated infections. The most widely used UV disinfection systems include 254 nm ultraviolet C (UVC) irradiation germicidal lamps. UV disinfection systems are primarily used in open spaces because 254 nm UVC can cause damage to the skin and eyes. Previous reports have shown that 222 nm UVC lines, which are part of the far UVC spectrum (207-222 nm), have highly effective germicidal properties and are safer for human eyes and skin than UVC at 254 nm. However, there are few reports on the disinfection effectiveness of 222 nm UVC in clinical settings. In this study, the extent of MRSA contamination on hand pieces used exclusively by physicians in hospitals was investigated, as well as the disinfection efficacy of 222 nm UVC on these devices.

Let’s dive right in now, and you can click on the question that interest you, 

1 Experimental sampling

From March 2020 to May 2020, 50 physician-specific cell phones for hospital use were sampled for bacterial contamination at the 746-bed Hiroshima University Tertiary Care Hospital, located in Hiroshima, Japan. A 25 cm2 tryptone soy agar (TSA, containing lecithin and polysorbate) contact disc stacked bioassay count (RODAC) plate was used for sampling (25 cm2; Nippon Becton Dickinson Co., Ltd., Tokyo, Japan). For sampling, the RODAC plate was pressed tightly against the surface of the phone button for at least 10 seconds.

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2 Bacterial culture and identification

Immediately after sampling, contact plates were sent to the clinical laboratory of Hiroshima University Hospital and incubated at 37°C under aerobic conditions for 48 hours. The total number of colony-forming units (CFU) of all aerobic bacteria (AB) in each sample was estimated after plate counting. MRSA colonies were identified based on the distinctive color and morphology of the colonies on the plates and the results of the S. aureus selective latex agglutination test (PS Latex; Eiken Chemical Co, Tokyo, Japan). They were then cultured in succession and identified using standard microbiological methods, and the CFU counts of MRSA in each sample were estimated.

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3 222 nm UV lamp sterilization efficacy of cell phones

To evaluate the actual efficacy of the 222nm UV lamp, 50 physician-use hospital phones were sampled and incubated before and after 222nm UVC disinfection (1.5 minutes per phone). 25 phones were sampled for the backside before disinfection and for the front side of the keys after 222nm UVC disinfection. For the remaining 25 phones, the front buttons were sampled before disinfection, and the backs were sampled after 222 nm UVC disinfection. For sampling, the RODAC tablet was pressed close to the surface of the phone’s keys or to the back of the phone 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.

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4 Results

Of the 0 cell phones, 5 (10%) were contaminated with MRSA. median ABCFU was 17 (range: 3-122), mean ± standard deviation of AB CFU was 25.2 ± 24.5. for MRSA positive samples, median MRSACFU was 3.5 (range: 0-6), mean ± standard deviation of MRSACFU was 3.4 ± 1.7. on the cell phone panel The mean reduction of log10MRSA CFU is shown in Table 1. the mean ± standard deviation of MRSACFU for the control panel was (9.43 ± 0.98) X 106. 222 nm UVC irradiation for 1.5 and 2.5 min (9 and 15 mJ/cm²) resulted in a mean reduction of log10MRSA CFU of 2.91 and 3.95, respectively. log10MRSA CFU The number of log10MRSA CFU decreased with increasing irradiation time.

Table 2 summarizes the utility of 222 nm UV disinfection for reducing AB contamination on physician-specific hospital handpieces. Prior to disinfection, there was no significant difference in the number of CFU on the front button and back of the two groups (p= 0.7). However, 222 nm UVC irradiation at 9 mJ/cm2 (0.1 mW/cm² for 1.5 min) significantly reduced AB contamination on the handpieces in both groups. Compared with baseline, 222 nm UVC irradiation reduced AB contamination by 93.4% and 94.7%, respectively.

Table 1 Efficacy of 222nm ultraviolet C (UVC,0.1mW/cm²) in reducing methicillin-resistant Staphylococcus aureus (MRSA) contamination
UVC irradiation for 1.5 minutes (9mJ/cm²)UVC irradiation for 2.5 minutes (15mJ/cm²)UVC irradiation for 5 minutes (30mJ/cm²)UVC irradiation for 10 minutes (60mJ/cm²)
log mean reduction ± SD2.91 ± 0.113.95 ± 0.054.86 ± 0.035.41 ± 0.12
SD, standard deviation
Control plate MRSA CFU mean ± SD of (9.43 ± 0.98) X 10⁶
Table 2 Total colony forming unit (CFU) counts and sample CFU ratios after disinfection of baseline and aerobic bacteria by 222 nm UV light at 9 mJ/cm² (0.1 nW/cm², 15 min)
The backside of the disinfectionFront button after 222 nm UV disinfection
Mean CFU±SD2.27±26.51.95±1.93
Median CFU (range)17.5(5-102)1(0-5)*
Proportion of sample CFU (%)20/20(100%)14/20(70%)
Total number of CFU554 39
The backside of the disinfectionFront button after 222 nm UV disinfection
Mean CFU±SD29.4±25.21.65±1.53
Median CFU (range)22.5(4-100)2(0-5)y
Proportion of sample CFU (%)20/20(100%)13/20(65%)
Total number of CFU58733
CFU, colony-forming unit; SD, standard deviation; UV
*P<.001 (before disinfection vs. after 222 nm UV disinfection)
yP<.001 (before disinfection vs. after 222 nm UV disinfection)