Patients can be at risk from ultrasound associated infections when low-level disinfection (LLD) is the standard of care. In order to quantify this risk, Scotland’s National Health Service undertook a retrospective analysis of microbiological and prescription data through linked national health databases. Patient records were examined in the 30-day period following semi-invasive ultrasound probe (SIUP) procedures.
The study analysed almost one million patient journeys that occurred during a six-year period from 2010.1
Of the 982,911 patients followed, 330,500 were gynaecological patients; and 60,698 of these gynaecological patients had undergone a transvaginal (TV) ultrasound procedure. These patients were found to be at a 41% greater risk of infection and a 26% greater risk of needing an antibiotic prescription in the 30 days following their transvaginal ultrasound procedure when compared to gynaecological patients who had not undergone a transvaginal ultrasound.
During the study period, 90.5% of facilities reported that they were performing low level disinfection for transvaginal ultrasound probes. These patients were at a greater risk of infection due to inadequate reprocessing and the study concluded that: “Hence failure to comply with existing guidance on [high-level disinfection] of SIUPs will continue to result in an unacceptable risk of harm to patients .”1
The diverse use of ultrasound probes is now prompting a renewed focus on correct probe reprocessing to ensure patient safety. To ensure best practice standards, decontamination experts and ultrasound users need to work together to reduce the risk of infection that is associated with using ultrasound probes.
Ultrasound procedures are performed in various inpatient and outpatient settings by a wide range of health professionals. This has increased the use of surface probes to guide procedures such as biopsies, cell retrieval, cannulation, catheterisation, injections, ablations, surgical aspirations, and drainages. Across these procedures, the probe has the potential to contact various patient sites
– including intact skin, non-intact skin, mucous membranes and sterile tissue. This presents a complex challenge, as contact with these various body sites requires differing levels of disinfection or sterilisation between patient uses. Failure to adequately clean and disinfect medical devices like ultrasound probes between patients poses a serious risk to patient safety.
In 2012, a patient in Wales died from a hepatitis B infection – most likely caused by a failure to appropriately decontaminate a transoesophageal echocardiography probe between patients. As a result of this fatality, a Medical Device Alert was issued by the Medicines and Healthcare Products Regulatory Agency (UK) advising users to appropriately decontaminate all types of reusable ultrasound probes.2
The UK and European guidelines require ultrasound probes that come into contact with mucous membranes and non-intact or broken skin to be high-level disinfected. In particular, automated and validated processes for ultrasound reprocessing are preferred. This is supported by a study relating to manual disinfection methods, which found that only 1.4% of reprocessing systems were fully compliant when using manual methods, compared to 75.4% when using semi-automated disinfection methods.3
The Spaulding classification system
The Spaulding classification system4 must be applied before a procedure commences so that information about what tissues or body sites may be contacted is taken into account.
This classification system is a widely adopted disinfection framework for classifying medical devices, based on the degree of infection transmission risk, and requires the following approaches:
- Critical devices are defined as those that come into contact with sterile tissue or the bloodstream. Probes in this category should generally be cleaned and sterilised. Where sterilisation is not possible, high-level disinfection is acceptable with the use of a sterile cover for ultrasound probes.
- Semi-critical devices contact intact mucous membranes and do not ordinarily penetrate sterile tissue. Ultrasound probes scanning over non-intact skin are also considered semi-critical. Semi-critical ultrasound probes include endocavitary probes, which should be used with a cover in addition to being high-level disinfected.
- Non-critical devices only contact intact skin. This category also includes contact surfaces that are not intended for patient contact in health settings. These devices and surfaces should be cleaned and low level disinfected.
It is important to note the difference between cleaning and low-level disinfection. Cleaning is the removal of soil and visible material until the item is clean by visual inspection. Low level disinfection is the elimination of most bacteria, some fungi and some viruses.
A final and important point for consideration is the use of probe covers.
While many ultrasound users and sonographers believe that their transvaginal ultrasound patients are protected from infection risk by using barrier shields and/or condoms, research has shown that up to 13% of condoms fail and up to 5% of commercial covers fail. Probe covers may have microscopic tears or breakages which can allow microorganisms to pass through.5
Ultrasound users should work with their decontamination colleagues to understand the current UK and European guidelines for reprocessing ultrasound probes. There are patient risks associated with ultrasound usage when proper disinfection procedures are not followed, as well as from ancillary
products such as contaminated ultrasound gel. While the increased use of ultrasound has brought many benefits for patients, effective education and disinfection protocols are required to minimise the risk of infection.
- Scott D et al. Risk of infection following semi-invasive ultrasound procedures in Scotland, 2010 to 2016: A retrospective cohort study using linked national datasets. Ultrasound 2018;26(3):168–77.
- Medicines and Healthcare products Regulatory Agency (MHRA). Medical Device Alert. Reusable transoesophageal echocardiography, transvaginal and transrectal ultrasound probes (transducers) Document: MDA/2012/037. 2012.
- Ofstead CL et al. Endoscope reprocessing methods: Prospective study on the impact of human factors and automation. Gastroenterol Nurs 2010;33(4):304–11.
- Spaulding EH. Chemical disinfection of medical and surgical materials. In: Lawrence C, Block SS, editor. Disinfection, sterilization, and preservation. Lea & Febiger Philadelphia (PA); 1968:517–31.
- Basseal JM, Westerway SC, Hyett JA. Analysis of the integrity of ultrasound probe covers used for transvaginal examinations. Infect Dis Health 2020 Mar;25(2):77–81.