
The term “hospital-required infection” or “nosocomial infection” was first mentioned in “In-Hospital Infection Control”, published by the American Hospital Association in 1968, as a microbial infection that occurred in a hos-pital1). Currently, this term has been replaced by a generic term called healthcare-associated infection, expanding to include not only patients but also hospital-related workers with infections in all medical-related institutions, such as nursing homes outside hospitals2). In Korea, research on infection control in hospitals began in 1991 and has be-come increasingly important over time3). Staphylococcus aureus, a major causative agent of medical-related infec-tions, causes a wide range of clinical conditions, including bacteremia, endocarditis, and osteomyelitis4). In particular, as resistance to antibiotics increased, methicillin-resistant S. aureus (MRSA) emerged, and later vancomycin was developed as a treatment for MRSA; however, vancomycin- resistant S. aureus also appeared5). The increased inci-dence of infected patients in medical institutions caused by these antibiotic-resistant bacteria has emerged as a global public health problem6).
The rapid spread of COVID-19 (coronavirus disease- 19), which first began in Wuhan, China, in 2019, led the World Health Organization (WHO) to declare a global pandemic in 2020 by announcing its official name due to its high pathogenicity and infectiousness, which continues to this day with mutations7,8). Since the COVID-19 pandemic, the importance of infection prevention and management has emerged in most medical institutions and infection-related organizations, and with this opportunity, related studies are being actively conducted along with the need for an infection control system9-11). COVID-19 is an infectious disease that poses a high risk of air infection, and dental institutions are at high risk of cross-infection due to the presence of large amounts of droplets and aerosols12). After the COVID-19 pandemic, the number of patients decreased significantly as anxiety about dental care increased13). Therefore, when respiratory infections such as COVID-19 and flu are prevalent, infection control at dentistry is very important compared to other medical institutions.
With the development of digital radiography devices, many dental institutions are currently using examination methods through radiography to diagnose patients and establish treatment plans. In particular, dental panoramic X-ray imaging, which can check the overall condition of the teeth and jawbones, is used for diagnosis and exami-nation in most visiting patients, so it is very frequent14). However, for dental panoramic photography, the risk of cross-infection is high because the skin directly contacts both the patient and the dental healthcare worker. Many studies have been conducted on the infectivity and bac-terial contamination of devices and equipment used in dental treatment rooms, such as dental chairs and hand-pieces, and both patients and dental healthcare workers recognize the importance of infection control15-17). However, since the panoramic imaging device is located separately in a radiographic room outside the dental treatment room, awareness of the importance of infection control is low despite contact with many people, and related research is insufficient.
COVID-19 has increased interest in and awareness of hygiene among many people. The control and prevention of infection in dental institutions are more important18). It is equally important to recognize the importance of infection control on dental radiography devices with which people frequently come into contact. Therefore, in this study, we visited randomly selected dental institutions and attempted to investigate the degree of bacterial contamination accor-ding to the contact area of digital panoramic dental X-ray equipment (PDX). By identifying S. aureus, an important causative agent of general aerobic bacteria (GAB) and medical-related infections, we aimed to present the need for infection control in radiation equipment and raise awa-reness among dental healthcare workers.
This study was conducted on PDX currently used in general hospitals, dental hospitals and clinics in Gyeongsangbuk-do from March 24 to May 5, 2023. The subjects of the investigation are a total of 13 PDXs: one from one general hospital, three from two dental hospitals, and nine from eight dental clinics. During panoramic X-ray imaging, the areas where the patient and the dental hygienist (operator) mainly came into contact were selected, and microorganisms were collected from the area. The contact areas of the patient were as follows: (1) left- handle, (2) right-handle, (3) forehead support, (4) head side support. The contact areas of the operator were as follows: (1) X-ray exposure switch, (2) left-click mouse button (Fig. 1).
A SWABON M-Swab kit (Microgiene, Suwon, Korea) was used to collect microorganisms by the PDX site. It was collected by rubbing 10 times with cotton swabs sterilized with up, down, left, and right sides of each area, and then placed in an individual transport medium containing 10 ml of physiological saline and sealed. The samples were equ-alized for 15 seconds with a vortex mixer and then 2 ml of the bacterial dilution solution was inoculated onto an Aerobic Count Plate and Staph Express Count Plate of 3MTM PetrifilmTM (3M Korea, Seoul, Korea) for GAB and S. aureus. The plates were cultured in a 35±1°C incubator for 48 hours. The CFU/ml of red and red-violet colonies formed in GAB and S. aureus were counted, respectively.
The normality of the data was confirmed using the Sha-piro-Wilk test. The difference in the CFU/ml of bacteria by PDX site was investigated by performing Kruskal- Wallis H verification, and the post-test was performed using the Dunn test. The difference in the CFU/ml of bac-teria by PDX site between hospital-level or higher insti-tutions and dental clinics was confirmed using the Mann–Whitney U test. In the PDX, the Mann–Whitney U test was used to verify the difference in bacterial count bet-ween patient contact and dental hygienist contact. The correlation between GAB and S. aureus by site of PDX was confirmed by Spearman sequence correlation analysis. All analyses were analyzed at the level of a=0.05 with IBM SPSS statistics ver. 27.0 (IBM Corp., Armonk, NY, USA).
Significant differences were identified in the CFU/ml of GAB according to the PDX area (p<0.001). A significantly higher GAB was found in the patient’s contact areas, right- handle, forehead support, and head side support, compared to the operator’s contact area, X-ray exposure switch, and left-click mouse button (p<0.05). No significant differe-nces were found in the left handle area, which is the area in contact with the patient, compared to the operator contact area (p>0.05; Table 1, Fig. 2).
Levels of General Aerobic Bacteria and Staphylococcus aureus in Each Part of Digital Panoramic Dental X-Ray Equipment (Unit: CFU/ml)
Bacteria | Part of the PDX | No. | Minimm | Median | Maximm | Mean rank | p-value |
---|---|---|---|---|---|---|---|
GAB | Left-handle | 13 | 1.50 | 9.00 | 94.00 | 31.69a,e | <0.001 |
Right-handle | 13 | 0.50 | 27.00 | 76.50 | 41.77a,d | ||
Forehead support | 5 | 28.50 | 59.50 | 69.00 | 57.40b,d | ||
Head side support | 10 | 5.00 | 33.00 | 118.00 | 48.05b,d | ||
X-ray exposure switch | 13 | 0.00 | 2.50 | 29.50 | 18.92e | ||
Left-click mouse button | 13 | 0.50 | 4.00 | 40.00 | 23.81e | ||
S. aureus | Left-handle | 13 | 1.00 | 3.50 | 59.00 | 34.27a,b | <0.001 |
Right-handle | 13 | 0.00 | 16.50 | 96.50 | 41.42b,c | ||
Forehead support | 5 | 16.00 | 32.50 | 104.50 | 58.60c | ||
Head side support | 10 | 3.00 | 15.75 | 34.00 | 44.95b,c | ||
X-ray exposure switch | 13 | 0.00 | 1.00 | 10.50 | 21.50a | ||
Left-click mouse button | 13 | 0.00 | 2.00 | 6.00 | 20.92a |
PDX: digital panoramic dental X-ray equipment, GAB: general aerobic bacteria.
The difference in letters a, b, c, d, and e mean that there was a significant difference in Dunn's post-test with multiple comparison test.
p-value obtained by Kruskal-Wallis test.
Significant differences were also identified in the CFU/ ml of S. aureus according to the PDX sites (p<0.001). A significantly higher S. aureus was found in the patient’s contact areas, right-handle, forehead support, and head side support compared to the operator’s contact areas, X-ray exposure switch, and left-click mouse button (p< 0.05). No significant difference was observed in S. aureus between left and right-handles (p>0.05; Table 1, Fig. 3).
We identified differences in GAB and S. aureus by divi-ding the contact area between the dental hygienist, the main operator of PDX, and the patient. As a result, there was a significant difference between the contact area bet-ween the patient and the dental hygienist in both GAB and S. aureus (p<0.001; Table 2).
Levels of GAB and Staphylococcus aureus per Contact Area by the Patient and Dental Hygienist of the Digital Panoramic Dental X-Ray Equipment
Mean rank (CFU/ml) | p-value | ||
---|---|---|---|
Patient | Dental hygienist | ||
GAB | 42.01 | 21.37 | <0.001 |
S. aureus | 42.11 | 21.21 | <0.001 |
GAB: general aerobic bacteria.
p-value obtained by performing the Mann–Whitney U test.
A significant correlation was confirmed between GAB and S. aureus in the left-handle (r=0.946, p<0.001) and the right-handle (r=0.941, p<0.001), respectively. Significant correlations between left-handle and right-handle were confirmed between GAB and GAB (r=0.700, p<0.001), between GAB and S. aureus (r=0.630, p<0.05), and between S. aureus and S. aureus (r=0.608, p<0.05). Significant correlations between forehead support and head side support were identified between GAB and GAB (r=−1.000, p< 0.001), between GAB and S. aureus (r=−1.000, p< 0.001), and between S. aureus and S. aureus (r=1.000, p< 0.001). The GAB detected in head side support was significantly correlated with the GAB of the left-click mouse button (r=−0.689, p<0.05), and with the S. aureus of forehead support (r=1.000, p<0.001), and with the S. aureus of head side support (r=0.721, p<0.05). The S. aureus detected in the head side support was significantly correlated with the S. aureus of the X-ray exposure switch (r=0.634, p<0.05). The GAB detected in the X-ray expo-sure switch was significantly correlated with the S. aureus detected in the same area (r=0.721, p<0.001). The GAB detected in the left-click mouse button was significantly correlated with the S. aureus (r=−0.900, p<0.05) of the forehead support and with the S. aureus (p=0.613, p<0.05) of the left-click mouse button, respectively (Table 3).
Correlation between GAB and Staphylococcus aureus by Digital Panoramic Dental X-Ray Equipment Areas
GAB | S. aureus | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Left-handle | Right-handle | Forehead support | Head side support | X-ray exposure switch | Left-click mouse button | Left-handle | Right-handle | Forehead support | Head side support | X-ray exposure switch | Left-click mouse button | |||
GAB | Left-handle | 1.000 | ||||||||||||
Right-handle | 0.700 |
1.000 | ||||||||||||
Forehead support | −0.100 | −0.300 | 1.000 | |||||||||||
Head side support | 0.262 | 0.394 | −1.000 |
1.000 | ||||||||||
X-ray exposure switch | 0.145 | −0.116 | −0.821 | 0.268 | 1.000 | |||||||||
Left-click mouse button | 0.047 | −0.313 | −0.200 | −0.689 |
0.039 | 1.000 | ||||||||
S. aureus | Left-handle | 0.946 |
0.681 |
−0.100 | 0.166 | 0.236 | 0.064 | 1.000 | ||||||
Right-handle | 0.630 |
0.941 |
−0.500 | 0.438 | −0.066 | −0.463 | 0.608 |
1.000 | ||||||
Forehead support | −0.700 | 0.100 | 0.100 | 1.000 |
−0.051 | −0.900 |
−0.700 | 0.600 | 1.000 | |||||
Head side support | 0.012 | 0.406 | −1.000 |
0.721 |
0.207 | −0.548 | 0.055 | 0.511 | 1.000 |
1.000 | ||||
X-ray exposure switch | 0.276 | 0.128 | −0.700 | 0.500 | 0.721 |
−0.050 | 0.336 | 0.156 | −0.100 | 0.634 |
1.000 | |||
Left-click mouse button | 0.064 | −0.172 | 0.200 | −0.480 | −0.192 | 0.613 |
0.068 | −0.201 | −0.100 | −0.560 | −0.291 | 1.000 |
GAB: general aerobic bacteria.
The correlation was analyzed by Spearman rank correlation coefficient. *p<0.05, **p<0.01.
The PDX, which is provided in most dental institutions, is an essential device for diagnosis and examination, and patients and dental workers come into contact with each other frequently14). With the development of various medi-cal radiation equipment, including PDX, their use has increased, and research on the risk, safety, and manage-ment of patient exposure doses is being conducted stea-dily14,19). However, despite the contact of many people, there is insufficient evaluation of the microbial contami-nation of equipment or research on the level of awareness of infection control among medical workers. In particular, studies on the risk of cross-infection in intraoral digital imaging among dental radiation equipment are often conducted, but there are few studies on extracoral radia-tion equipment20).
In dental clinics, dental hygienists mainly guide and photograph patients regarding PDX use. Therefore, we identified the microbial contamination of PDX by disting-uishing between the part that the patient comes in contact with and the part that the dental hygienist comes in contact with. Consequently, S. aureus, an important causative agent of medical-related infections, as well as GAB, was detected at all sites of the PDX where the patients and dental hygi-enists were in contact. This is consistent with previous findings that Staphylococci were detected in both periapical and panoramic X-ray machines21). In particular, the CFU/ml of bacteria was highest in PDX’s forehead support, followed by the head side support area. Because the presence or absence of forehead support and head side support varies depending on the PDX model, many bacteria were detected even though the number of subjects was small. Both of these areas are considered to be highly contaminated with bacteria because they are the areas that the patient’s hair mainly touches. Studies isolating and analyzing S. aureus from humans showed that more than 70% were present in the hair, and it was also reported that antibiotic-resistant bacteria were isolated from the hair of inpatients22,23). Therefore, in PDX, forehead support and head side support are areas that can cause cross-infection; therefore, it is necessary to disinfect each patient or manage it using disposable films.
Among the PDX handles in contact with the patient, bacteria were measured more on average in the right- handle than in the left-handle. This is presumed to be the result of the microorganisms being buried while using the right hand, as there are far more right-handed than left- handed people. This can also be predicted from the results of a study on microbial contamination of the hand measured before, after, and during the cooking process of restaurant cooks, which showed that microbial contamination of the right hand was higher than that of the left hand24).
In the PDX contact microbial contamination results, the mean rankings of GAB and S. aureus were approximately twice as high in patients as in dental hygienists. This is thought to be due to the fact that the area in contact with the equipment was narrower for dental hygienists than for patients. However, S. aureus was also identified in the X- ray exposure switch of the PDX, and the left-click mouse button of the computer was used to check the radiographs or send photos. Moreover, a significant correlation bet-ween GAB and S. aureus was observed at most of the PDX sites. These results suggest the cross-infection may occur not only in patients but also in dental healthcare workers, including dental hygienists. As dentistry is a me-dical institution that is frequently exposed to blood and saliva and has a very high risk of cross-infection with aero-sols, the emergence of S. aureus may cause purulent infec-tions in dentistry patients, which may be fatal for immu-nocompromised patients4,25).
As a result, as many bacteria were detected in PDX, which generally have a low awareness of infection control, this study can be presented as a basis for the need for infection control in places or equipment that are easy to miss.
In this study, we investigated the contamination of PDX limited to GAB and S. aureus, but did not identify various types of microorganisms such as facultative anaerobes and fungi observed in dental clinics. Additionally, this research was conducted in some dental institutions extracted from convenience in some areas of Gyeongsangbuk-do, and each institution did not confirm how to control PDX infection. In the future, evaluating microbial contami-nation of PDX according to the level of awareness and practice of infection control by dentists or dental hygie-nists will be necessary.
None.
Conflict of Interest
Ji-Hyun Min has been journal manager of the Journal of Dental Hygiene Science since January 2023. Ji-Hyun Min was not involved in the review process of this study. No potential conflict of interest relevant to this article was reported.
Ethical Approval
Not applicable.
Author contributions
Conceptualization and funding: Ki-Rim Kim. Super-vision and Formal analysis: Ji-Hyun Min. Experiments: Lee-Rang Im. Data acquisition: Lee-Rang Im. Writing–original draft: Lee-Rang Im. Writing-review & editing: Ki-Rim Kim and Ji-Hyun Min.
Funding
None.
Data availability
Raw data is provided at the request of the corresponding author for reasonable request.
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