Decontamination of ultrasound equipment used for ...

Anaesth Intensive Care 2013; 41: 529-534

Decontamination of ultrasound equipment used for peripheral ultrasound-guided regional anaesthesia A. Chuan*, C. Tiong†, M. Maley‡, J. Descallar§, H. Ziochos** Department of Anaesthesia, Liverpool Hospital, Liverpool, New South Wales, Australia

Summary Portable ultrasound machines are frequently used in operating theatres for peripheral single-shot nerve block procedures. This equipment must be decontaminated by reducing the microbial load to a sufficient level to reduce the risk of nosocomial infection. In our institution we use a simple three-step decontamination protocol utilising 70% isopropyl alcohol as chemical disinfectant. We performed a prospective, quality assurance study to assess the efficacy of this protocol, as it is unclear if this is suitable for disinfecting semicritical equipment. The primary endpoint was presence of microbial contamination prior to re-use of equipment. Over a four-week period, 120 swabs were taken from multiple sites on our ultrasound machines and linear array transducers for microbial culture. Swabs were taken after decontamination and immediately prior to patient contact. Any pathogenic and environmental bacterial organisms were isolated and identified. No pathogenic organisms were grown from any of the collected swabs. In 85% (n=102) of cultures, no growth was detected. Of the remaining 15% (n=18), commensal organisms commonly found on skin, oral and environmental surfaces were isolated. Our results suggest that our decontamination protocol may be an effective, rapid and cost-effective method of cleaning ultrasound equipment used for peripheral invasive single-shot nerve blocks. Further guidance from national bodies is required to define appropriate cleaning protocols for these machines. Key Words: decontamination, ultrasound equipment, regional anaesthesia

Nosocomial infection is common in hospital patients, resulting in significant morbidity and mortality, and is a large economic burden for society1–4. Known vectors for transmission of pathogenic microorganisms are ultrasound transducers and ultrasound coupling gel, both of which have been implicated in outbreaks of hospital acquired infection5–8. Reusable medical equipment such as ultrasound machines and transducers must thus undergo the process of decontamination, reducing the microbial load to a sufficient level to prevent clinically significant infection. The Spaulding classification is used to categorise equipment according to exposure, with higher thresholds of microbial eradication required for equipment at greater risk of exposure9. While there are guidelines for transducers used in a surgical field and for intra-cavity insertion10–13, there are no universally adopted recommendations * MB, BS (Hons), PGCertCU, FANZCA, Consultant Anaesthetist. † MB, BS, FANZCA, Consultant Anaesthetist. ‡ MB, BS, FRACP, FRCPA, Director, Department of Microbiology and Infectious Diseases. § MBiostat, Biostatistician, Ingham Institute for Applied Medical Research. ** BAppSc, MPH, Senior Hospital Scientist, Department of Microbiology and Infectious Diseases, Sydney South West Pathology Service, Sydney. Address for correspondence: Dr A. Chuan. Email: [email protected] Accepted for publication on April 19, 2013. Anaesthesia and Intensive Care, Vol. 41, No. 4, July 2013

for decontamination of ultrasound machines and transducers used for peripherally invasive procedures such as single-shot ultrasound-guided regional anaesthesia. There is a wide variation in practice regarding the level of sterility, such as the use of transducer sheaths and sterile gloves, as well as nonuniform decontamination protocols. Institutions have instead adopted local policies based on multiple factors including cost, feasibility and compliance. To our knowledge, no published data exist on the efficacy of different practices in decontaminating ultrasound equipment used in operating theatres. We designed this study to assess the effectiveness of a simple three-step decontamination protocol utilising 70% isopropyl alcohol as the disinfectant for ultrasound equipment used to perform singleshot, peripheral ultrasound-guided nerve blocks. The primary outcome was determining if the ultrasound equipment used for these procedures and processed using this protocol had been sufficiently disinfected to allow its use in the next patient. METHODS Ethical approval for this study was granted by the South Western Sydney Local Health District Human Research and Ethics Committee (project approval

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A. Chuan, C. Tiong et al

LNR/12/LPOOL/93) for Liverpool Hospital, Sydney, Australia. Registration in the Australian and New Zealand Clinical Trials Registry was declined as the study design was deemed an observational study (request number 00363031). In our institution, single-shot peripheral ultrasoundguided nerve blocks are performed without sterile transducer sheaths or use of transparent adhesive film covers. Skin asepsis is performed using 2% chlorhexidine and 70% isopropyl alcoholimpregnated wipes prior to needle insertion. There is no departmental policy on the use of sterile gloves and sterile fenestrated drapes or trays; this is left to individual preference. After use, the ultrasound machine and transducer are decontaminated in a three-step process. Initially, physical cleaning to remove visible soiling is performed using a non-sterile, single-use, dry cloth towel. Next, the equipment is sprayed and then wiped with another single-use cloth towel soaked with a clear volatile liquid containing 70% isopropyl alcohol as active constituent (Transeptic cleaning solution, Parker Laboratories, New Jersey, USA). Lastly, the machine is passively air dried. The ultrasound machine is then placed in the anaesthesia supplies storeroom, ready for re-use. This simple process is performed by anaesthetic assistants who have received prior instruction on these steps and typically takes less than five minutes. In this study, a total of 120 samples were collected randomly from our four identical ultrasound machines (SonoSite M-Turbo, SonoSite Inc., Washington, USA) at different times of the day, on different days of the week, over a four-week period in July 2012. This period encompasses a typical month of clinical workload in our institution. Samples were taken in the anaesthetic bay or in the anaesthetic storeroom. The anaesthesia staff who decontaminate the machines were blinded to the purpose of this study. One author (CT), trained to correctly collect microbiological samples, performed all sampling wearing sterile gloves and using a sterile swab stick. To ensure adequate capture, the swab stick was moistened with sterile saline and rubbed over each sampling site ten times. Labelled swabs were immediately transported to the laboratory for inoculation onto horse blood agar plates (bioMérieux Australia Pty Ltd, Baulkham Hills, Australia), a nonselective culture medium designed to support growth of commonly encountered micro-organisms. Cultures were incubated for 48 hours at 37°C in aerobic conditions. The plates were examined by another author (HZ) blinded to sample collection, at both 24 hours and 48 hours. Organisms were identified using Matrix Assisted Laser Desorption/Ionisation—

Time of Flight mass spectrometry (MALDI-TOF MS Biotyper 2, Bruker Daltonics GmbH, Bremen, Germany). This system is reliable and accurate in identifying micro-organisms14,15. Five sampling areas were chosen for their repeated contact with either the proceduralist or the patient. These were the gain control knobs, depth buttons, touchpad, the neck of the linear array transducer and the faceplate of the linear array transducer. Where an area had multiple potential sites, the swab was wiped over each site; for example, the depth control swab was wiped over both depth control buttons. Sixty samples were taken within 30 minutes of the decontamination procedure, allowing for air-drying of the disinfectant (Post-Decontamination [PD], Group PD), and 60 samples were taken at least 30 minutes after decontamination but immediately prior to patient contact (Pre-Patient Contact [PPC], Group PPC). Thus, each sampling area identified on the ultrasound machine was swabbed in total 24 times, with 12 samples in each Group PD and Group PPC. The time periods for swab collection were purposed to reveal if initial decontamination was adequate and if previously decontaminated equipment continued to be risk-free just before patient use. Statistical analysis Fisher’s exact test was applied to determine statistical significance between rates of contaminated samples in paired groups: 60 samples each in Groups PD and PPC, and 12 samples in each group between five sampling sites. RESULTS Total samples Of the 120 samples collected, 85% (n=102) exhibited no growth after 48 hours of incubation. No pathogenic or multi-resistant bacterial organisms were detected. Of the 15% (n=18) of samples demonstrating growth, organisms isolated were typical skin flora (Kocuria kristinae, and multiple coagulase negative Staphyloccus species including S. epidermidis, S. hominis, S. saprohyticus, S. cristatus, S. capitis, S. haemolyticus), oral flora (Neisseria mucosa, N. falvescens, Rothia mucilaginosa, Streptococcus oralis, and Streptococcus mitis), or environmental flora (Bacillus thuringensis). A total of 9.2% (n=11) were skin flora, 4.2% (n=5) were oral flora, and 1.7% (n=2) were environmental flora. There were nine positive plates each from Group PD and Group PPC. Group PD Of 60 samples in Group PD, nine samples (15%) had positive growth. All positive culture plates had scant growth, defined as 100 mixed colonies of skin flora S. epidermidis and S. capitis. Specific organisms and location are summarised in Table 2. All calculated P values were >0.05, range 0.22 to 1.00, suggesting insufficient evidence for a statistical difference between any of the compared groups. DISCUSSION The results of our study show that a simple, threestep decontamination process utilising 70% isopropyl alcohol as disinfectant was effective in preventing growth of known bacterial pathogenic organisms on ultrasound equipment used for ultrasound-guided single-shot blocks. No microbial growth was found in 85% of the total samples. In the majority of the remaining samples, scant growths of commensal skin, oral and environmental flora was isolated. The Spaulding classification describes decontaminating medical equipment according to risk

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of infection. It categorises equipment as critical (high risk of infection), semi-critical (equipment in contact with mucous membranes or non-intact skin) and non-critical (equipment in contact with intact skin)9,16. Under this classification, ultrasound equipment used in operating theatres may encompass all three: intraoperative liver ultrasound (critical), transoesophageal echocardiography and insertion of indwelling intravascular or perineural catheters (semi-critical), or transthoracic echocardiography (non-critical). Governmental bodies and national society guidelines stipulate that non-critical equipment should be decontaminated with low level disinfectants10–13. Several studies have demonstrated the micro-organism burden of ultrasound equipment used in this context, and the effectiveness of different methods of disinfection. Mattar and colleagues17 took 440 swabs prior to decontamination from the keyboard, probe, probe holder and ultrasound coupling gel. Their three ultrasound machines were used for non-invasive diagnostic scanning in a general population attending a radiology department. Multiple isolates of known pathogenic bacterial organisms, including Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa and two types of Acinetobacter species, including one isolate with antibiotic resistance, were observed. Growth of organisms fell by 45% after paper towel wiping only, and decontamination was 98% effective after a second clean with soap and water. In a quality assurance sweep, Sykes et al18 grew S. aureus, haemolytic Streptococci, E. faecalis,

Table 1 Positive culture results in Group PD Gain control knobs (n=1)

Depth buttons (n=4)

Keyboard touchpad (n=2)

Linear probe— Linear probe—faceplate neck (n=0) (n=2)

Four colonies of mixed S. mitis, S. oralis

One colony of K. kristinae One colony of S. capitis Nil One colony of S. cristatus Five colonies of S. oralis Four colonies of S. hominis Four colonies of S. hominis

Eight colonies of S. epidermidis One colony of Bacillus species

Number of plates with growth (n) and identified organisms and colony counts. PD=post decontamination. Table 2 Positive culture results in Group PPC Gain control knobs (n=1)

Depth buttons (n=2)

Keyboard touchpad (n=0)

Linear probe—neck (n=3)

Linear probe—faceplate (n=3)

One colony of S. haemolyticus

One colony of S. waneri >100 colonies of mixed growth S. epidermidis, S. capitis

Nil

Two colonies of S. hominis One colony of S. saprohyticus One colony of S. oralis

Confluent B. thuringensis One colony of N. mucosa, Mixed growth: two colonies of N. falvescens, one colony of R. mucilaginosa, and eight colonies of S. oralis

Number of plates with growth (n) and identified organisms and colony counts. PPC=pre-patient contact. Anaesthesia and Intensive Care, Vol. 41, No. 4, July 2013

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Enterococcus faecium (non-vancomycin resistant strain), and Acinetobacter species from their three ultrasound machines in a radiology suite. Of their 180 swabs, 65% were contaminated with skin and environmental flora, 9.4% grew known bacterial organisms and only 25.6% had no growth. Their decontamination protocol specified wiping the keyboard and probe holder with detergent at the start and end of the day. Probes were used without a sheath and gel was wiped clear between patients but not necessarily cleaned with disinfectant (aqueous chlorhexidine or 70% alcohol) unless used on a known or suspected infected patient. Use of an intermediate level disinfectant results in better decontamination rates. Karadenz et al19 collected 37 samples after performing diagnostic scans in the abdominal, axillary and inguinal regions. A total of 27 (73%) exhibited confluent growth before cleaning, reducing to one plate of >50 colony forming units after cleaning with dry paper then 70% alcohol wipes. Fowler and McCraken20 published similar results after their probes were used on known methicillin-resistant S. aureus patients in the intensive therapy unit. In 40 samples, they grew an average of 128 colony forming units per plate after patient use, and 0.5 colony forming units per plate after paper then 70% alcohol wipes. Two benchtop studies where probes were deliberately inoculated with pathogenic bacteria such as methicillin-resistant S. aureus, P. aeruginosa, or E. coli showed a reduction to 0.01% of the original inoculant cell count6 and no growth22 after disinfection with 70% alcohol and quaternary ammonia impregnated wipes, respectively. In contrast to these studies discussing diagnostic scanning, ultrasound-guided regional anaesthesia (and other invasive procedures in interventional radiology and critical care medicine) involves skin puncture and possible contamination by blood onto the transducer. If these applications are argued to be semi-critical, it mandates full sterilisation or the use of a sterile sheath followed by prolonged immersion with a high-level disinfectant10–13. Enforcing this level of decontamination will impose an extra burden on limited theatre staff and reduce availability of equipment already under high demand. It is also unclear whether this level of decontamination is required or a modification is acceptable. In our study, after single-shot ultrasound-guided regional anaesthesia procedures, our results indicate that all 120 swabs were clear of known pathogens, both in Group PD and Group PPC. There was no statistical difference between growth rates in all five sampling areas or between samples taken from

machines recently decontaminated versus machines stored and ready for use. In Group PD, scant growth of predominantly skin flora replicates results from other studies, showing that isopropyl alcohol at 60 to 90% strength is an effective intermediate level disinfectant within ten seconds of application, as it is highly bactericidal, tuberculocidal, fungicidal and virucidal12,23. The low level of commensal organisms detected in our cultures is clinically insignificant if the machine is subsequently used on a patient with a normal immune system24. No growth would have been preferable, and suggests either inadequate cleaning or a break in protocol. A factor that contributes to inadequate cleaning may be the design of our machine keyboard and touchpad. Figure 1 illustrates the recessed depth buttons and grooves on the gain control buttons. These niches may potentially harbour biological material that would be difficult to clean and difficult to penetrate with disinfectants. In Group PPC, two swabs exhibited heavy growth and confluent growth in the depth buttons and probe faceplate respectively. This suggests original inadequate decontamination or re-contamination. The latter may be caused by staff members inadvertently touching the machine or droplet spread while in the storeroom. Our storeroom also contains other portable theatre equipment and consumable stock and is exposed to staff traffic. This would suggest that re-cleaning the transducer with 70% isopropyl alcohol and air drying immediately prior to next patient use is not unreasonable. There are several limitations to our study. The adherence to the decontamination protocol by anaesthesia assistants was not examined. The

Figure 1: Sampling areas on the ultrasound equipment. 1=linear array transducer faceplate, 2=linear array transducer neck, 3=gain control knobs, 4=depth buttons, 5=touchpad. Gain control knobs are recessed and grooved. Depth control buttons are recessed. Anaesthesia and Intensive Care, Vol. 41, No. 4, July 2013

Decontamination of ultrasound machines used for peripheral RA effectiveness of any protocol is dependent on the staff correctly performing the task. However, this study was conducted in a four-week period of normal activity in the operating theatre suite with different staff involved in decontamination and our results are perhaps reflective of true-life compliance rates. No data were collected on the infectious status of admitted patients with whom our machines came into contact. The use of probe covers and the decontamination process remained the same during the study period irrespective of infective status. The lack of pathogenic bacterial organism growth in our study in Group PD is reassuring, particularly since 11% of patient admissions to our tertiary level trauma hospital are methicillin-resistant S. aureus swab positive25. Establishing a causal link between the nosocomial transmission of a specific organism from patient to equipment to patient would require genotyping techniques not used in this study. In our institution, probe covers are not used for single-shot blocks and we avoid using adhesive transparent film dressings on the transducer as any residual adhesive left on the probe can potentially encourage microbial colonisation. Failure of commercial sterile sheaths are not uncommon26 and thus even with use of probe covers, the recommendations for semi-critical probe processing remains unchanged and high-level disinfection by immersion is mandated13, but use of covers and sterile gloves may improve overall decontamination rates. An absolute reduction in contamination was not measured in our study as sampling was not performed immediately after use. Probes have been heavily contaminated after use in radiology17–19, intensive care20, hospital wards5,27 and in the emergency department22. In particular, our study did not address if the use of probe covers in patients with known multi-resistant organisms would have reduced the absolute contamination rates in the operating theatre. Decontamination success of the curvilinear transducer, which is also used in single-shot ultrasoundguided blocks, and of machines from other manufacturers was not assessed. This is a pertinent limitation of our study as the shape and presence of biological niches such as grooves may limit generalisation of our results to different ultrasound equipment. We note that manufacturers have begun to address these issues by designing newer models with flat surface keyboards and non-recessed control buttons. We also caution that each equipment manufacturers’ recommendations of compatible disinfectants are continually updated28 and that the most current advice should be sought for each Anaesthesia and Intensive Care, Vol. 41, No. 4, July 2013

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individual ultrasound machine system and transducer. In conclusion, this study reports the effectiveness of a protocol used in our institution to process the linear array transducer and ultrasound system that is used for peripherally invasive single-shot ultrasound-guided nerve blocks. Our results suggest that 70% isopropyl alcohol, recommended for noncritical disinfection, may also be used to reduce decontamination of semi-critical equipment to a lowrisk level for nosocomial transmission. Successful decontamination of probes used with sterile covers, or after use in patients with multi-resistant organisms, will require clarification. Last, further guidance from national bodies is required to define a decontamination policy that is effective and acceptable on issues of cost, feasibility and compliance in the operating theatre. References 1. Rosenthal VD, Bijie H, Maki DG, Mehta Y, Apisarnthanarak A, Medeiros EA et al. International Nosocomial Infection Control Consortium (INICC) report, data summary of 36 countries, for 2004-2009. Am J Infect Control 2012; 40:396-407. 2. . National Nosocomial Infections Surveillance (NNIS) System Report, data summary from January 1992 through June 2004, issued October 2004. Am J Infect Control 2004; 32:470-485. 3. Centers for Disease Control. Scott RD. The direct medical costs of Healthcare-Associated Infections in US hospitals and the benefits of prevention. From http://www.cdc.org/HAI/burden.html. Accessed January 2013. 4. Health Protection Agency. English National Point Prevalence Survey on Healthcare Associated Infections and Antimicrobial Use 2011: Preliminary data 2012. From http://www.hpa.org. uk/webc/HPAwebFile/HPAweb_C/1317134304594. Accessed January 2013. 5. Muradali D, Gold WL, Phillips A, Wilson S. Can ultrasound probes and coupling gel be a source of nosocomial infection in patients undergoing sonography? An in vivo and in vitro study. AJR Am J Roentgenol 1995; 164:1521-1524. 6. Ohara T, Itoh Y, Itoh K. Ultrasound instruments as possible vectors of staphylococcal infection. J Hosp Infect 1998; 40:73-77. 7. Gaillot O, Maruejouls C, Abachin E, Lecuru F, Arlet G, Simonet M et al. Nosocomial outbreak of Klebsiella pneumoniae producing SHV-5 extended-spectrum beta-lactamase, originating from a contaminated ultrasonography coupling gel. J Clin Microbiol 1998; 36:1357-1360. 8. Weist K, Wendt C, Petersen LR, Versmold H, Ruden H. An outbreak of pyodermas among neonates caused by ultrasound gel contaminated with methicillin-susceptible Staphylococcus aureus. Infect Control Hosp Epidemiol 2000; 21:761-764. 9. Spaulding EH. Chemical disinfection of medical and surgical materials. In: Lawrence C, Block SS, eds. Disinfection, Sterilization, and Preservation. Philadelphia: Lea & Febiger 1968. p. 517-531. 10. American Institute of Ultrasound in Medicine. Guidelines for cleaning and preparing endocavitary ultrasound transducers between patients June 2003. From http://www.aium.org/ resources/statements.aspx. Accessed November 2012.

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11. Australasian Society for Ultrasound in Medicine. Statement B2: Statement on the disinfection of transducers March 2012. From http://www.asum.com.au/newsite/files/documents/policies/PS/B2_policy.pdf. Accessed November 2012. 12. Centers for Disease Control. Rutala WA, Weber DJ, Healthcare Infection Control Practices Advisory Committee. Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008. From http://www.cdc.gov/hicpac/Disinfection_Sterilization/ acknowledg.html. Accessed January 2013. 13. Food and Drug Administration. Guidance for Industry and FDA staff: information for manufacturers seeking markeing clearance of diagnostic ultrasound systems and transducers September 2008. From http://www.fda.gov/downloads/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/UCM070911.pdf. Accessed January 2013. 14. Neville SA, Lecordier A, Ziochos H, Chater MJ, Gosbell IB, Maley MW et al. Utility of matrix-assisted laser desorption ionization-time of flight mass spectrometry following introduction for routine laboratory bacterial identification. J Clin Microbiol 2011; 49:2980-2984. 15. Valentine N, Wunschel S, Wunschel D, Petersen C, Wahl K. Effect of culture conditions on microorganism identification by matrix-assisted laser desorption ionization mass spectrometry. Appl Environ Microbiol 2005; 71:58-64. 16. Sabir N, Ramachandra V. Decontamination of anaesthetic equipment. Cont Educ Anaesth Crit Care Pain 2004; 4:103-106. 17. Mattar EH, Hammad LF, Ahmad S, El-Kersh TT. An investigation of the bacterial contamination of ultrasound equipment at a university hospital in Saudi Arabia. J Clin Diagn Res 2010; 4:2685-2690. 18. Sykes A, Appleby M, Perry J, Gould D. An investigation of the microbial contamination of ultrasound equipment. Br J Infect Control 2006; 7:16-20.

19. Karadenz YM, Kilic D, Kara Altan S, Altinok D, Guney S. Evaluation of the role of ultrasound machines as a source of nosocomial and cross-infection. Invest Radiol 2001; 36:554-558. 20. Fowler C, McCracken D. US probes: risk of cross infection and ways to reduce it—comparison of cleaning methods. Radiology 1999; 213:299-300. 21. Ohara T, Itoh Y, Itoh K. Contaminated ultrasound probes: a possible source of nosocomial infections. J Hosp Infect 1999; 43:73. 22. Frazee BW, Fahimi J, Lambert L, Nagdev A. Emergency department ultrasonographic probe contamination and experimental model of probe disinfection. Ann Emerg Med 2011; 58:56-63. 23. Schabrun S, Chipchase L. Healthcare equipment as a source of nosocomial infection: a systematic review. J Hosp Infect 2006; 63:239-245. 24. Casadevall A, Pirofski LA. Host-pathogen interactions: basic concepts of microbial commensalism, colonization, infection, and disease. Infect Immun 2000; 68:6511-6518. 25. Schmidt H, Ryan E, Maley M, van Hal SJ. MRSA admission burden and acquisition in a tertiary care hospital. BMC Proc 2011; 5:S6:27-29. 26. Rooks VJ, Yancey MK, Elg SA, Brueske L. Comparison of probe sheaths for endovaginal sonography. Obstet Gynecol 1996; 87:27-29. 27. Kibria SMG, Kerr KG, Dave J, Gough MJ, HomerVanniasinkam S, Mavor AID. Bacterial colonisation of Doppler probes on vascular surgical wards. Eur J Vasc Endovasc Surg 2002; 23:241-243. 28. FujiFilm SonoSite Inc. Disinfectants for SonoSite products, version 09, February 2013. From http://www.sonosite.com/sites/ default/files/support_docs/Disinfectants_ENG_P06703-09A_e. pdf. Accessed April 2013.

Anaesthesia and Intensive Care, Vol. 41, No. 4, July 2013