High level disinfection (HLD) is defined as the complete elimination of all microorganisms in or on an instrument, except for small numbers of bacterial spores. Instruments classified as semi-critical devices require high level disinfection.
Ultrasound transducers can be classified as a semi-critical device if/when it comes in contact with non-intact skin.
The classification system first proposed by Dr. E. H. Spaulding divides medical devices into categories based on the risk of infection involved with their use. This classification system is widely accepted and is used by the Food and Drug Administration (FDA), the Centers for Disease Control and Prevention (CDC), epidemiologists, microbiologists, and professional medical organizations to help determine the degree of disinfection or sterilization required for various medical devices. Three categories of medical devices and their associated level of disinfection are recognized.
A device that enters normally sterile tissue or the vascular system or through which blood flows should be sterile. Such devices should be sterilized, which is defined as the destruction of all microbial life.
A device that comes into contact with intact mucous membranes and does not ordinarily penetrate sterile tissue. These devices should receive at least high-level disinfection, which is defined as the destruction of all vegetative microorganisms, mycobacterium, small or nonlipid viruses, medium or lipid viruses, fungal spores, and some bacterial spores.
Devices that do not ordinarily touch the patient or touch only intact skin. These devices should be cleaned by low-level disinfection.