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Comparison of the Degree of Bacterial Removal by Hand Hygiene Products
J Dent Hyg Sci 2022;22:51-6
Published online March 31, 2022;  https://doi.org/10.17135/jdhs.2022.22.1.51
© 2022 Korean Society of Dental Hygiene Science.

Young Sun Hwang

Department of Dental Hygiene, College of Health Science, Eulji University, Seongnam 13135, Korea
Correspondence to: Young Sun Hwang, https://orcid.org/0000-0001-7012-3434
Department of Dental Hygiene, College of Health Science, Eulji University, 553 Sanseong-daero, Sujeong-gu, Seongnam 13135, Korea
Tel: +82-31-740-7493, Fax: +82-31-740-7352, E-mail: kiteys@eulji.ac.kr
Received January 17, 2022; Revised February 10, 2022; Accepted February 24, 2022.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Background: The coronavirus disease (COVID-19) pandemic increased awareness regarding the importance of hand hygiene in infection prevention. Although social distancing and vaccination are the strongest ways to prevent infection, personal hand hygiene is the most basic and easiest way to maintain public health. However, in addition to hand washing using running water, sanitizing tissues, and disinfection products are convenient for hand hygiene, especially outdoors. Therefore, it is necessary to improve the appropriateness of individual hand hygiene methods. In this study, we investigated the degree of hand hygiene offered by various hygiene products and hand drying methods for maintaining hand hygiene.
Methods: An LED UV light kit was used for fluorescent observation of hand contamination. Bacteria from the hands were cultured to compare the degree of hand hygiene offered by various hygiene products. Bacteria were cultured in a hand-shaped medium dish to identify areas vulnerable to hand hygiene. Moreover, the degree of hand hygiene was observed according to the drying method using bacterial cultures.
Results: We confirmed that hand washing under running water with antibacterial soap, sanitizing with alcohol gel disinfectant, and wiping with antibacterial wet wipes was effective for hand hygiene compared to washing under running water alone. However, for all hygiene products, a large number of bacteria were detected on the fingertips. We verified that natural drying, rather than rubbing, is effective in maintaining hand hygiene.
Conclusion: These results suggest that hand hygiene products and drying methods are critical in hand hygiene management. Therefore, these results provide a basis for determining whether an individual’s hand hygiene management method is appropriate.
Keywords : Disinfectants, Hand disinfection, Hand sanitizers, Hygiene, Infections
Introduction

Various vaccines and treatments are being developed as human lives are threatened by the 2019 novel coronavirus disease (COVID-19) pandemic. It has been confirmed that wearing masks and washing hands are effective in preventing infectious diseases1). The number of outpatients with respiratory and ophthalmic diseases has significantly decreased in 2020 compared to 2018 because of wearing masks and washing hands during the pandemic2). Washing hands effectively reduces bacteria; therefore, the consumption of hand disinfectants and sanitizers to prevent infectious diseases has also increased rapidly3). Washing hands with soap reduces the incidence of infectious diseases by 40 to 50%4).

In addition to washing hands under running water, alcohol gels and wet wipes are widely used for hand hygiene. Hand disinfectants containing ethanol and isopropanol are effective in killing bacteria and viruses, and hand sanitizers, such as soap, wash away bacteria and viruses by removing the oily layer on the skin surface. Therefore, hand sanitizers are auxiliary means for handwashing and are more effective in removing bacteria and viruses compared to water washing. A comparison of the effect of reducing the number of bacteria after handwashing with antibacterial soap, alcohol hand sanitizer, and wet wipes showed that alcohol hand sanitizers are effective in removing bacteria5). However, there have been no studies identifying vulnerable washing areas and comparing the degree of bacterial removal according to hand hygiene products and drying methods.

In this study, the hand hygiene effects of antibacterial soap, alcohol gel disinfectant, and antibacterial wipe were compared with those of water washing using fluorescent observation and bacterial culture methods. Based on these results, we intend to provide hand hygiene management information to individuals and medical staff participating in clinical treatments.

Materials and Methods

1. Subjects

Thirty-four Eulji University students (Sungnam campus) who understood the purpose of this study and voluntarily agreed to participate were included. The study was conducted with a limited number of people participating in social distancing because of concerns about COVID-19. The students participated in the experiment without washing their hands within 3 hours before the experiment. Students excluded from the experiment were as follows: those with hand wounds, eczema, and dermatitis and those who had experienced abnormal symptoms with alcohol or soap.

2. Hand hygiene methods

The four hand hygiene methods were performed as follows: hands were washed under running water, washed under running water with antibacterial soap, sanitized with alcohol gel disinfectant, and wiped with antibacterial wet wipes. Handwashing under running water was performed for 30 seconds according to the six steps of hand washing suggested by the Ministry of Health and Welfare (https:// www.youtube.com/watch?v=1A_gj_c0Krc). Sanitizing with alcohol gel disinfectant and wiping with antibacterial wet wipes were also performed for 30 seconds. Manufacturers of hand hygiene products include Labccin V3 antibacterial soap (Aekyung Industrial Co., Seoul, Korea), 70% ethanol sanitizer 9270 gel (Korea 3M Co., Seoul, Korea), and sanitizing wet wipes (0.1% benzalkonium chloride; Yuhan-Kimberly, Seoul, Korea).

3. Fluorescence observation

An LED UV light kit (my-UV007; Myeong Moon Medical Instruments, Seoul, Korea) was used for fluorescent observations. After applying the inspection lotion according to the manufacturer’s protocol, we observed the fluorescence level in the view box and acquired the image. The image was converted to 8 bits black and white using the ImageJ software (National Institutes of Health, Bethesda, MD, USA) to measure the bright areas.

4. Bacterial culture

Brain Heart Infusion (BHI) agar (BD Difco, Sparks, MD, USA) was prepared in a 100 mm petri dish and used for experiments after drying the excess moisture on the medium surface. The palm surface was evenly contacted with a sterilized cotton swab for 10 seconds and then smeared onto the agar plate. The bacteria were cultured overnight in an incubator at 37°C, and the number of bacterial colonies was counted. The BHI agar medium was also prepared in a hand-shaped dish, and the entire palm was brought into contact. Bacteria were cultured overnight at 37°C. The number of bacterial colonies in the hand- shaped dishes was counted.

5. Statistics

Statistical analyses were conducted using the InStat GraphPad Prism ver. 5.01 statistical software (GraphPad Software Inc., San Diego, CA, USA). The results are expressed as mean±standard deviation. The non-parametric Kruskal–Wallis test with Dunn’s post-hoc analysis was employed for multiple comparisons. p<0.05 was considered to indicate statistical significance.

Results

1. Comparison of contamination removal based on hand hygiene products

Participants first evenly applied a fluorescence inspection lotion on their hands and then acquired the entire hand image. Subsequently, hand hygiene was performed with four hand hygiene products, and the residual fluorescence was observed. Images were acquired and compared with fluorescence levels of the before hand hygiene image. A decrease in fluorescence was observed in hand hygiene using running water; however, it was not significant. A significant decrease in fluorescence was observed after washing hands under running water with antibacterial soap, sanitization with alcohol gel disinfectant, and wiping with antibacterial wet wipes. However, a significant amount of residual fluorescence was observed on the fingertips in all the methods, except for wiping with antibacterial wet wipes (Fig. 1).

Fig. 1. Comparison of contamination removal based on hand hygiene products. Fluorescence lotion was smeared evenly on the whole hand and hand hygiene was performed with four hand hygiene products. The fluorescence was observed using the LED UV light kit according to the manufacturer’s protocol. The image was acquired and compared with the fluorescence levels of before and after images using the ImageJ software. *p<0.01, **p<0.001 versus before. B/W: black/white, ns: non-specific.

2. Comparison of bacteria control based on hand hygiene products

Bacteria collected from the participants’ palms with a cotton swab were smeared on an agar medium plate. Subsequently, hand hygiene was performed with the four hand hygiene methods, and the hands were dried completely by rubbing. Then, the bacteria on the palm were collected with a cotton swab, smeared on an agar medium plate, and cultured. In the case of hand hygiene using running water, no difference in bacterial colony number was observed before and after washing. However, washing under running water with antibacterial soap and sanitizing with antibacterial wet wipes and alcohol gel disinfectant decreased the number of bacterial colonies compared to before hand hygiene; however, a significant number of bacteria were still detected (Fig. 2).

Fig. 2. Comparison of bacterial growth control based on hand hygiene products. Bacteria were collected from the participants’ palms with a cotton swab before and after hand hygiene with four hand hygiene products and cultured on a 100 mm agar plate. Hands were dried by rubbing after hand hygiene. Bacterial colonies are shown in the red spot. The number of bacterial colonies was measured in 8 bits black and white image using the ImageJ software. A representative result was shown. *p<0.01, **p<0.001 versus before. ns: non-specific.

3. Comparison of bacteria control based on hand hygiene products according to drying methods

According to a previous report, rubbing for drying after hand washing has less effect on reducing bacterial numbers compared to drying naturally; in contrast, it increases bacterial numbers6). To confirm the cause of the detection of a significant number of bacteria even after hand hygiene, we compared bacteria detected by rubbing and drying hands after hand hygiene and the naturally drying method. The alcohol gel was spread evenly over the entire hand and dried naturally. For this experiment, a hand-shaped agar plate capable of monitoring bacteria throughout the palm was used. In the drying method by rubbing hands, a decrease in the number of bacteria was observed compared to before hand hygiene; however, a large number of bacterial colonies were still detected (Fig. 3). This was similar for all four hand hygiene methods. In particular, a large number of bacteria were detected on the fingertips, consistent with the weak areas of hand hygiene confirmed by fluorescence (Fig. 1). In air-drying after hand hygiene, the number of bacterial colonies on the entire palm significantly reduced compared to before hand hygiene, and fewer bacterial colonies were measured compared to rubbing for drying. In addition, fewer bacterial colonies were detected in hand hygiene under running water with antibacterial soap, sanitizing with alcohol gel disinfectant, and wiping with antibacterial wet wipes compared to hand hygiene under running water alone. This result indicates that using a hand hygiene product with antibacterial function is more effective in reducing the number of bacteria compared to washing with only water and minimizing contact of both hands until completely dry, compared to rubbing hands, to reduce the number of bacteria.

Fig. 3. Comparison of bacteria control by hand hygiene products according to drying methods. Bacteria on the palms before and after hand hygiene with four hand hygiene products were cultured on a hand-shaped agar plate. Hands were dried by rubbing or air dried after hand hygiene. Bacterial colonies are shown in the red spot. Bacterial colonies were counted and graphed. *p<0.01, **p<0.001 versus before. #p<0.01 versus rubbing. ns: non-specific.
Discussion

Generally, hand hygiene has been emphasized for workers in special occupations, such as operation rooms, medical personnel, and cooks. In dental clinic, the hands of medical personnel are frequently exposed to saliva, blood, and contaminants. Therefore, the necessity of providing regular educational programs is suggested for the practice of infection prevention7). Personal hand hygiene has become very important for public health because of the COVID-19 pandemic. Although the Korean Centers for Disease Control and Prevention recommends six steps of hand washing for infection control, there are many difficulties in carrying them out properly during outdoor activities. Therefore, the use of portable antibacterial wet wipes and alcohol gel disinfectants has increased in recent years. Antibacterial soaps are also widely used.

Ethanol and isopropanol are the most commonly used active ingredients for hand sanitizers and are quasi-drugs that sterilize and disinfect the skin to prevent infection8). Benzalkonium chloride is widely used for disinfection and as a preservative in pharmaceuticals and cosmetics9). Unlike hydrogen peroxide or ethanol, 0.1% benzalkonium chloride does not cause local toxicity, such as skin irritation, eye mucous membrane irritation, and skin sensitization; therefore, it is also used as a disinfectant for children’s wounds. In contrast, hand sanitizers are used to wash hands with water. It removes the oily layer on the skin surface and bacteria and viruses attached to the skin. Theoretically, hand sanitizers can effectively remove contaminants. In this study, four hand hygiene methods were tested to control the number of bacteria on the hand surface and to compare areas that were vulnerable to washing. We used a method of washing hands with only water, washing with water using soap, and a hygiene method that is used without water, such as alcohol gel disinfection and antibacterial wet tissue. A significant decrease in the number of bacteria was observed in all hand hygiene methods except for washing with running water only. Among them, washing with running water using antibacterial soap and sanitary methods using alcohol gel disinfectants reduced the number of bacteria more effectively. However, a significant number of bacteria were detected after hand hygiene. In particular, fluorescence analysis revealed that the fingers and surrounding areas were the least cleansed. These results suggest that the four hand hygiene methods reduce the number of bacteria; however, a significant number of bacteria remain, and fingertip hygiene requires more attention. According to previous reports, there was no difference in the sterilization and cleaning effects of regular and antibacterial soaps10). An insufficient amount of alcohol gel hand sanitizer and insufficient drying time are less effective in removing bacteria10).

In addition, the degree of bacterial growth was observed based on the drying method after hand washing. Our experimental results confirmed that the drying method is also important for maximizing hand hygiene. The natural drying method was more effective in reducing the number of bacteria compared to drying by hand rubbing after hand washing. Consistent results have also been reported by other researchers. Upon comparing the bacterial removal effect of three methods: a paper towel, a hand dryer while rubbing hands, and a hand dryer without hand rubbing, bacteria on the palms and fingers were found to be greatly reduced when the hands were dried with a hand dryer without rubbing, and fingertip bacteria were significantly reduced when paper towels were used for drying8,9). In contrast, when the hand was dried with a hand dryer while rubbing, bacteria increased3,6). Kim et al.7) also reported that the number of bacterial colonies significantly increased after handwashing compared to before handwashing, regardless of using paper towels or cotton towels. These results suggest that the drying method should be carefully considered for hand hygiene management.

In conclusion, in this study, the hygiene effects of frequently used hand hygiene products and the degree of hand hygiene according to the drying method were observed. In addition to washing hands using soap, alcohol gel sanitizers and wet wipes are also effective for hand hygiene management. Moreover, it was confirmed that hand drying without rubbing was effective in maintaining hand hygiene. Therefore, the hand drying method should be considered for effective hand hygiene management.

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2018R1D1A1B07042035).

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Ethical Approval

Human experiment was approved by the Institutional Review Board (IRB) of Eulji University (approval No. EU21-017).

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