Ⅰ. Introduction
On March 11, 2020, the World Health Organization (WHO) declared coronavirus disease 2019 (COVID-19) as a ‘pandemic’, the highest level of infectious disease risk. Recently, there has been an increase in the use of ultrasound technology and consequently, there is a need to evaluate the efficacy of infection control measures in the ultrasound room to prevent cross-infection.
In general, hospital ultrasound equipment consists of a functional keyboard, track ball, various ultrasound probes, and ultrasound gel. Among these, the probe comes in direct contact with the patient, acting as a detector that acquires images for observation of the internal anatomy and the disease-associated abnormalities. Various types of probes exist, each with a different frequency that can be selected based on the purpose and the anatomical structure to be observed during the procedure. Recently published reports have revealed that bacterial contamination on ultrasound probes is much higher than that found on public toilet seats and bus poles, not to mention that pathogens in surface contaminants can survive for a longer time[1,2]. Ultrasound procedures require a substance that eliminates the presence of air between the probe and skin surface, for which an ultrasound gel is generally used. This gel is characteristically highly viscous and made of smooth material as it acts as a contact medium between the piezoelectric material of the ultrasound probe and skin surface. However, due to its high viscosity, the risk of cross-contamination and secondary nosocomial infection increases if the gel on the probe is not completely removed or disinfected after examination, as the same probe is used on different patients[3]. Although established guidelines for disinfection and sterilization are universally available[4], numerous secondary infections have occurred due to lack of compliance[5,6]. The sharing of devices and instruments between multiple patients with different diseases in hospitals may lead to nosocomial infections. Nosocomial infections occur when patients and hospital staff themselves become the source and means of infection transmission; acting as carriers and contaminating the surrounding environment including the air, solutions, assistive devices, and medical devices, leading to new infections[7,8].
It has been reported that an 82% improvement in surface decontamination through cleaning and disinfection could lead to a 68% reduction in nosocomial infections caused by the contamination of surroundings[9,10]. The number and type of pathogens that can lead to nosocomial infections has exponentially risen with the development of medical technology. This risk has further escalated due to the ongoing COVID-19 pandemic, drawing social interest and thereby emerging as an important aspect in the evaluation of hygiene in the hospital environment. Extensive research has been conducted on the contamination levels and disinfection methods of existing medical equipment and various solutions have been proposed[11,12]. While there are many different disinfection methods that show varying results, all methods demonstrated good outcomes with regard to the prevention of infection[6,13,14].
Therefore, in this study, samples were collected using the double swab technique[15], and bacterial contamination was evaluated before disinfection. To raise hygiene awareness and emphasize the importance of contamination management, this study compares the contamination levels between ultrasound rooms in hospitals, where strict contamination management protocols are presumably in place, and everyday objects that numerous people encounter.
Ⅱ. Materials and methods
In this study, surfaces of eight different ultrasound room objects were evaluated, specifically the accessories of the ultrasound system (Accuvix A30, Samsung Medison Co., Korea): ultrasound probes (convex, linear, sector, and 3D), ultrasound track ball, ultrasound keyboard, and ultrasound gel (sealed and in use) as well as an ultrasound room pillow. The four types of ultrasound probes were sampled at the handle and crystal, the areas that come in most contact with the examiner and the examinee. Additionally, to compare the contamination levels between items used in the ultrasound room and everyday objects, subway handles, common PC keyboards, common PC mouse, and cell phones were sampled (Fig. 1).
First, the double swab technique[15] was used to collect samples (one-time sample collection) from the ultrasound room and everyday objects using sterile cotton swabs and a transport medium (Fig. 2). All sample collections were performed without sterilization after an ultrasound diagnosis was completed. Since the sampling area was different for each collection site, each sample was obtained by swabbing as wide an area as possible. A transport medium was used to minimize cell death during transportation or during delays in inoculation or cell culture. Two cotton swabs were enclosed, one for Gram staining and the other for culture. The cotton swabs used for sample collection were sealed in long, individual sample containers and then sent to a clinical pathology laboratory (LabGenomics, Co., Korea) for culture and identification. Depending on the type of sample or microorganism to be cultured, an appropriate medium was selected for inoculation, for which the streak plate technique was used[16,17]. After 24 h, the sample cultures were observed for colony formation. Upon detection of unusual colony morphology, the cultures were observed for up to 48 h.
Ⅲ. Results
Table 1 shows the results of contamination levels in the ultrasound room and everyday objects. Six bacterial strains were detected in the convex probe, linear probe, sector probe, 3D probe, ultrasound track ball, ultrasound keyboard, ultrasound gel (sealed and in use), and ultrasound room pillow, among which 83.3% were gram-negative and 16.7% were gram-positive. The gram-positive bacterial strains were methicillin-resistant Staphylococcus aureus (MRSA) and Micrococcus luteus, whereas the gram-negative bacterial strains were Moraxella osloensis, Acinetobacter baumannii, Acinetobacter lwoffii, Burkholderia gladioli, and Candida guilliermondii. Moraxella osloensis was the most common strain and accounted for 42.9% of the detected bacteria.
Four strains were detected from everyday objects, subway handles, common PC keyboards, common PC mouse, and cell phones, of which 75.0% were gram-negative (Klebsiella oxytoca, Acinetobacter baumannii, and Moraxella osloensis) and 25.0% were gram-positive (Micrococcus luteus). Objects found in the ultrasound room had a higher distribution of gram-negative bacteria than everyday objects. Fig. 3 shows the number of bacterial species detected in the ultrasound room and everyday objects, and the ratio of the gram-positive and gram-negative bacteria at each collection site.
Ⅳ. Discussion
Microorganisms that inhabit the surfaces of devices and accessories used for medical treatment (i.e., ultrasound probes) can infect patients, clinical staff, and the surface of tools, thereby increasing the rate of nosocomial infections. Without effective infection control policies in place, insufficient disinfection can lead to increases in infections from these microorganisms[18,19]. Therefore, this study aimed to raise awareness regarding the importance of infection control within the ultrasound room by identifying bacteria that may cause infection and by comparing the type and number of bacteria found on the surfaces of everyday objects to those on the objects found in the ultrasound room. However, the number of targeted bacteria was limited. Despite this limitation, there was little difference in the number of bacterial strains detected on the objects found in the ultrasound room (six bacterial strains) compared to those on everyday objects (four bacterial strains). The cell phone was the only object on which bacteria were not detected. This may be due to the fact that cell phones are often cleaned or disinfected regularly depending on the user.
On ultrasound room objects, Moraxella osleoensis was found on both the sector probe and common PC mouse; similarly Acinetobacter baumannii was found on both the 3D probe and common PC keyboard. Various bacterial strains were detected on the probes that come into close contact with the patient’s skin during the procedure. MRSA, detected on the convex probe, is a bacterium that is resistant to penicillin antibiotics and can lead to serious problems such as purulent (pus-forming) abscesses, sepsis, pneumonia, endocarditis, meningitis, osteomyelitis, and surgical site infection[20,21]. MRSA can be transmitted via contact with infected patients or carriers (such as clinical staff) or through the environment, such as by contact with medical equipment and beds. Contrastingly, Moraxella osloensis is a bacterium that is rarely infectious to humans but is responsible for locker-room smells or shower-curtain odors[22].
Candida guilliermondii was detected in the ultrasound gel in use while Burkholderia gladioli was present in unopened gel bottles which is uncommon. Caution must be taken as pathogens can survive and proliferate within the gel. Thus, unless the gel is clearly labeled as “sterile,” it cannot be assumed to be free of pathogens. Bottle warmers, used for patient convenience to heat up gels that are too cold, must be cleaned and disinfected regularly. Keeping the bottle warm for long durations is not recommended as it aids bacterial growth[11].
The outer membrane of gram-negative bacteria like Moraxella osloensis or Acinetobacter lwoffii is comprised of lipopolysaccharides (LPS), which contain endotoxins that can cause a toxic reaction if released into the circulatory system. They can also lead to septic shock, which involves fever, hyperventilation, and hypotension, and can be potentially fatal[18].
Our results indicate shortfalls in hygiene management in the ultrasound room, deeming it no less risky for infection than the daily environment. The presence of microorganisms on frequently used objects in the ultrasound room highlights the importance of establishing and following strict infection control policies. Infections that can be transmitted via direct contact can be prevented by the use of disposable gloves. Disposable masks and gloves should be worn when coming into contact with others to avoid inhalation of droplets from a patient with a respiratory infection. In addition to the thorough disinfection of all the ultrasound equipment, frequent handwashing using regular soap, disinfectant, or alcohol-based gel hand sanitizer are recommended[23,24].
Thus, further studies on the proper cleaning and disinfection of equipment, a regular follow-up of standard protocols, and education of ultrasound technicians about hygiene are recommended for efficient hygiene management of ultrasound equipment and accessories.
Ⅴ. Conclusion
Instruments used in the ultrasound room for patient diagnoses can be a vehicle for infecting patients. Medical institutions should follow strict hygiene and infection control policies to minimize the risk of cross-infection and nosocomial infections. Thus, recognition of the importance of infection control, along with thorough disinfection before and after procedures is essential to prevent bacterial growth and nosocomial infections.
