Ultrasound has become a cornerstone in the diagnosis and treatment of patients in many hospital disciplines of medicine and surgery and is increasingly being used in Critical Care, Emergency Departments (A&E), Anaesthesia, and indeed Primary Care and Specialty Outpatient Clinics. To achieve the full ultrasound benefits in patient care, medical teams need to consider the contamination risk over repeated use of probes as a vector for pathogen transmission.
Various global guidelines have been published. But in response to current infectious diseases, specialty medical groups are publishing their own recommended guidelines, taking into account how ultrasound is practiced within their Specialty (Intensive Care, Emergency/A&E, Anaesthesia, Fertility Specialist), which is relevant to the wider medical community.
Based on these new emerging specialty guidelines, there are 10 recommendations to consider for ultrasound probe disinfection to prevent pathogen transmission during ultrasound use:
These recommendations address the emerging issues of care for patients with confirmed or suspected Corona Virus Disease 2019 (COVID-19) or potential risk to other infectious diseases Methicillin-resistant Staphylococcus aureus (MRSA) and High Risk Human papillomavirus (HPV). HPV is known as the silent killer that causes 99% all cervical cancers and associated with 5% of all cancers worldwide.7-9
1. Know When to Disinfect
To know what disinfection level to apply to the ultrasound probe before a patient procedure, refer to the Spaulding classification.
Under the Spaulding classification the ultrasound probe is classified into non-critical probe, semi-critical probe and critical probe, determined by how the probe comes in contact with the patient’s procedure site and the level of cross-infection risk.1-6
Non-critical probe is low- level disinfected as the probe contacts intact skin or non-infected skin and the potential cross-infection risk is low.
Semi-critical probe is high level disinfected as the probe may contact non-intact skin (wound or burn) or mucus membrane and the potential risk of cross-infection is considered medium to high.
Critical probe should be sterilised, if not possible can be high level disinfected and placed inside a sterile cover to prevent the contamination of a sterile field. The potential risk of cross-infection is considered high.
Low level Disinfectant: Kills most vegetative bacteria and some fungi and viruses but does not kill mycobacteria or bacterial spores.
High Level Disinfection: All viable microorganisms must be destroyed, except a small number bacterial spores
Sterilisation: All viable microorganisms must be destroyed
2. Ultrasound-guided procedures
Most ultrasound-guided procedures in A&E Departments and Intensive Care are urgent and are performed with live guidance involving sharp objects, such as needles, trocars and scalpels.
The setting presents an elevated risk of unintended micro or macro perforation of the sterile plastic probe cover, resulting in exposure of the patient and the equipment.
In response to the absence of clear evidence of harm as well as concerns to the practicality of HLD after ultrasound-guided procedures, the global guidelines1-6 permit LLD if the clinician judges that the transducer has not contacted “blood or body fluids noted during procedure” from potential contamination. The term “Noted” offers excessive ambiguity. That is why HLD is the only option in ultrasound-guided procedures
Considering all risks, specifically to POCUS in A&E and Intensive Care practice, as well as the minimal time and cost difference between options, HLD is preferred and recommended over LLD as the standard of care following ultrasound-guided procedures.10-13
3. Obstetrics Gynaecologists Procedures
Some institutions and medical teams proceed to Low Level Disinfection (LLD) and may not be fully aware of the cross-infection risks after use of an ultrasound probe that is classified as semi-critical. However, LLD has been proven to be insufficient, as demonstrated by the results of a retrospective cohort study using linked national datasets from Scotland.4-5 Standards and guidelines recommend HLD as a minimum for semi-critical probes.
The risk of exposure to toxic residuals can impact oocyte retrieval, embryo transfer and other IVF applications during pelvis ultrasound probe procedures. Included phenol, hydrogen peroxide (30% w/v), formaldehyde (37% w/v), Sodium hypochlorite (4% w/v), glutaraldehyde (50% w/v), cupric ascorbate, and peracetic acid (32% w/v) toxicity.11-12
Select high level disinfection system proven to kill high-risk, cancer-causing HPV. Research reveals that virtually all cervical cancers (more than 99%) are caused by high-risk Human Papillomaviruses (HPV16 and HPV18 ).13
HPV is a highly resistant virus; more so than other non-enveloped viruses previously tested. Published test results showed that commonly used clinical disinfectants, including those used as sterilants in medical and dental healthcare facilities, have no effect on HPV16 and HPV18.14
Results suggest that healthcare facilities using endocavity ultrasound probes need to strongly consider disinfection methods that are effective against native HPV - adopting new technologies such as UV-C HLD.15
Dr. Craig Meyers, Ph.D. - gives his expertise in HPV research. He was the first lab to develop a technique to grow natural High-Risk HPV. He discusses how his research has been applied in changing clinical practice globally in ultrasound probe reprocessing. Webinar
Webinar - HPV Facts
Dr. Craig Meyers, Ph.D. - gives his expertise in HPV research. HPV best research evidence supports clinical change in Ultrasound probe reprocessing
Q&A - Latest tests discussion
Dr. David J. Weber - What to Consider in Evidence-Based Practice in Ultrasound
4. Ultrasound Machine and Probe
Immediately cleaning following use, prevents drying and adherence of biological debris which may interfere with disinfection later.
Disinfection immediately before use minimises the risk of probe contamination. Individual policies must consider these factors in designing workflows reflecting local specifics.
Cleaning and Disinfection must apply to the entire ultrasound scanning equipment to adequately control the transmission of pathogens
High-frequency touch areas such as the keyboard, screen and probe holder are at risk of exposure to pathogens and require disinfection.1,7
Place ultrasound probe inside a clean cover may avoid contamination of probes following disinfection.
5. Use of Sterile Probe Covers
Sheath covers are mandatory for semi-critical procedures such as transrectal and trans-vaginal probes and critical procedures require a sterile sheath covers for procedures such as ultrasound-guided vascular access and intra-operative ultrasound.
Research studies show that up to 13% of condoms and 5% of commercial covers have tears pre and post-transvaginal ultrasound examinations.16-19 However, this integrity is subjectively estimated rather than factually proven. Most clinicians performing these procedures on a routine basis with high patient turnover can attest to the fact that perforation of the cover does occur, exposing the patient procedure site to cross-infection risk.20
In similar studies in Transoesophageal Echocardiography (TOE) studies question whether the cover sheath offers any advantage in reducing infection risk.21-26 As cleaning and disinfection are still needed to prevent probe contamination, it is not clear whether the cover sheath offers any advantage over standard measures for infection prevention.
Sheaths are subject to perforation which may be undetectable to the naked eye. Perforation rates are as high as 4.4%.21,23
Studies concluded, probes should undergo high level disinfection before each procedure and question whether sheath covers provide any advantage in reducing cross-infection risk.24-26
6. Use of Ultrasound Gel
Transmission of infection with ultrasound gel has been well reflected in the medical literature.27-30 Reusable containers present high-risk to patients due to potential for contamination of gel and bottle surface. While their use may be acceptable in low-risk situations, are high infection risk in A&E Departments and Critical Care.
Research studies clearly demonstrates that contaminated gel can lead to infections, but also highlight that a probe can be a vector for pathogen transmission.
Single-use sachets of sterile ultrasound gel are relatively cheap and present the best option to minimise potential contamination and cross-infection between patients. Routine warming of the gel is not recommended due to the increased risk of bacterial proliferation.
7. Documentation and traceability
Documentation of HLD must include the date and time, scanner and transducers identifiers, the name of the person performing disinfection and chemical agents with batch numbers. This documentation must be stored for a period prescribed by the local policy.
To reduce cross-infection risk, it is preferable to have electronic documentation, moving to a paperless system
8. Infection Control Risk Assessment
The Infection control risk assessment aim is to keep the patient and medical staff safe and is a living document that forms the foundation of any comprehensive Infection Prevention and
Control (IPC) program.48-49
The ultrasound probe risk assessment is designed to determine the risk for each hazard by how bad (Severity of Harm) and how likely the potential harm (likelihood of Harm) can occur during the reprocessing (cleaning, disinfection, and traceability) of ultrasound probes.
Risk Matrix, example below, could be used to determine risk for each hazard: (how bad and how likely) and consequently identify risk prominence and areas for improvement
9. Educational Training Videos – Certify Training
Most A&E and Intensive Care ultrasound studies are performed as a point of care investigations (POCUS), ranging from basic to highly advanced.31-46
Emergency Physicians and Intensive care doctors are traditionally responsible for cleaning and disinfection of ultrasound equipment. A survey of ICU and ED departments found that 50% of probes retained traces of blood despite current cleaning/disinfection regimes.46 This presents a clear danger to other patients, staff and visitors.
Adequate training in disinfection is needed due to significant variability of skills in infection control standards.
Healthcare companies that sell disinfection products need to provide educational tools to support training of medical staff in how to reduce cross-infection risk. They need to be available as either online training or in the form of training videos with certification option that training has been completed.
10. Current methods of disinfection
Ultrasound probes cannot be sterilised and there are a number of different disinfection methods shown in the table below.
Different manufacturers produce an array of different products, each with advantages and disadvantages that are best assessed according to local needs.
Options exist for all disinfection methodology with and without need for the purchase of upfront capital equipment.
For clinical workflows that require a 10-minute patient examination time, with a 5-minute turnaround time (such as Women’s Health, Fertility Medicine, IVF, Emergency, Intensive care), Chronos is extremely efficient in quickly disinfecting ultrasound probes between patients to help maximise patient throughput.
Other HLD systems can take significantly longer, directly impacting the number of examinations that can be achieved per day.