Selection of the “right” sterilization or disinfection process, or technology, for reprocessing a specific type of reusable instrument may not always be straightforward. This is often because the instrument is damaged by heat and, therefore, cannot be easily and cost-effectively sterilized using pressurized steam.

For many types of reusable heat-sensitive instruments capable of transmitting diseases during a medical procedure, low-temperature sterilization technologies and robust disinfection processes were developed. To be sure, selection of the appropriate reprocessing technology is crucial to quality, safety and the prevention of healthcare-associated infections (HAIs).

In general, the documented risk of infection associated with the reuse of a instrument (i.e., low, moderate, high), contaminated with potentially pathogenic microorganisms, dictates whether its disinfection or sterilization is required to prevent disease transmission.

The following strategy explains how to select an appropriate reprocessing procedure for a specific type of reusable medical instrument.

Step 1.  Determine the reusable device’s “classification.”

The first step in this process is to determine whether the instrument is classified as “critical,” “semi-critical,” or “non-critical.”  Table 1, below, may be used to simplify this determination.

* * * * *

Table 1: A widely accepted classification scheme for medical instruments.

A. Critical instruments penetrate sterile tissue, enter the vasculature, or contact the patient’s blood.

  • Examples include cardiac catheters, biopsy forceps, and implants.

B. Semi-critical instruments, in contrast, are limited to contacting mucous membranes (e.g., those of the gastrointestinal [GI] tract, the pulmonary tract, or the oral cavity) or non-intact skin.

  • Examples include GI endoscopes, “ENT” (ear-nose-throat) endoscopes, cystoscopes, and the blades and handles of rigid laryngoscopes.(1-4)

[Need to buy a colonoscope, laryngoscope, or flexible cystoscope? Click the link.]

  • The risk of infection associated with instruments in this category, while still potentially significant, is less than that of critical instruments.

Click here to read Dr. Muscarella’s related blog “The Reprocessing of Sheathed “ENT’ Endoscopes and Cystoscopes.”

Click here to read Dr. Muscarella’s related blog “On Reprocessing Skin Electrodes.”

C. Noncritical instruments, on the other hand, do not directly contact the patient, or only contact the patient’s intact skin.

  • Examples include blood pressure cuffs, stethoscopes, and bedpans. Other examples of non-critical devices include environmental surfaces, such as walls, floors, and sink tops.

[In the market to buy a stethoscope, blood pressure cuff, or bed pan? Click the link.]

  • Non-critical instruments pose the least, and a low, risk of infection if contaminated at the time of their use and contact with patients.

Click here to read Dr. Muscarella’s related blog “Decontamination of CPR Manikins.”

[Are you in the market to buy a CPR manikin? Click the link.]

* * * * *

Step 2. Understanding the differences between sterilization and the three levels of disinfection.

The next step in this process is to understand the differences between disinfection and sterilization.

Whereas sterilization is an absolute term that may be used to refer to processes that destroy all types of infectious agents, disinfection is a relative term, and processes that achieve it are classified into one of “three levels,” depending on their relative effectiveness. The higher the level of disinfection, the more effective the process.

Click here to read about a auditing program developed by Dr. Muscarella specifically designed to prevent infection-control breaches and associated infections (HAIs).

Presented another way, the more resistant the microorganism, the higher the level of disinfection (or sterilization) required to destroy it.  Table 2, below, explains the differences between the three levels of disinfection and sterilization.

* * * * *

Table 2. The definitions, characteristics, and relative effectiveness of sterilization and disinfection’s three levels.

A.  Processes that achieves sterilization:

  • are absolute, meaning they destroy all microorganisms, including bacterial endospores;
  • are sporicidal, tuberculocidal, virucidal, fungicidal, and bactericidal;
  • use bacterial endospores as biological indicators; and
  • are regulated by the Food and Drug Administration (FDA).

Agents that achieve sterilization include pressurized steam, ethylene oxide gas, hydrogen peroxide plasma. Sterilization is used primarily to prevent reusable critical instruments from transmitting disease during their reuse.

[Are you in the market to buy a steam autoclave or a steam sterilizer?  Click the link.]

B. Processes that achieve high-level disinfection (or, “HLD”):

  •  destroy all pathogenic microorganisms, including some types of (but not all) bacterial endospores during relatively short exposure times;
  • typically destroy high numbers of bacterial endospores during long exposures times;
  • are sporicidal (limited), tuberculocidal, virucidal, fungicidal, and bactericidal;
  • use mycobacteria as indicators of effectiveness; and
  • are regulated by the FDA.

[Are you in the market to buy Cidex OPA, Metricide (14-day), RapicideMetricide OPAResert XL, or Cidex (14-day) to high-level disinfect your instruments? Click the link.]

Agents that achieve HLD include 2% glutaraldehyde, 7.5% hydrogen peroxide, and 0.2% peracetic acid. HLD is used primarily to prevent reusable semi-critical instruments from transmitting disease during their reuse.

C. Processes that achieve intermediate-level disinfection (or, “ILD”):

  • destroy many types of microorganisms including mycobacteria;
  • are not sporicidal (note: in general, processes that achieve high-level disinfection are ordinarily sporicidal, like sterilization, but, unlike sterilization, may require extended exposure times (e.g., 32 hours) to destroy bacterial endospores);
  • are tuberculocidal, virucidal, fungicidal, and bactericidal;
  • may use mycobacteria and/or viruses as indicators of effectiveness; and
  • are regulated by the Environmental Protection Agency (EPA).
3 thoughts on “Disinfection or Sterilization of a Contaminated Reusable Instrument?”
  1. Dr. Muscarella – per usual – very well written and important essay. I appreciate your passion and understanding of the infection control/RME reprocessing continuum and utilize your studies extensively when training staff in reprocessing.
    Thank You!

    1. Dear Ms. Bala,

      It is nice to hear from you, and I thank you for taking the time to pose your question. I do intend this year to perform a product evaluation of the Trophon device. (To read my product evaluation of “disposable” irrigation tubing, which I just published, please refer to this link: My article will provide guidance for the Trophon’s safe and effective use. My evaluation will likely include some of the following advice:

      First, I found a YouTube video that demonstrates the clinical use of this device: Consider reviewing it.

      Second, while it is a new product with a limited track record, the Trophon EPR is novel, interesting, and may add value to the fields and arsenals of instrument reprocessing and infection control. When performed correctly, automated reprocessing may have some advantages compared to manual reprocessing.

      I have not worked with or encountered this device in the field, however, so, admittedly, my knowledge of its operation, safety, and effectiveness is limited. Nonetheless, I have a few recommendations, comments and questions that you might consider and investigate to learn more about the Trophon EPR’s suitability and cost-effectiveness for processing ultrasound transducers.

      (1) The Trophon EPR is cleared by the FDA for the high-level disinfection of “ultrasound transducers” (in about 7 minutes). So, first, consider clarifying with its manufacturer whether the Trophon EPR is cleared to disinfect *all* types of ultrasound transducers/probes (including transesophageal echocardiography, or TEE, probes; transrectal probes; and endovaginal probes) from all manufacturers including, for example, GE Healthcare (i.e., the apparent marketer of the Trophon EPR);

      or, whether there are some types of transducers (which ones?) marketed by some companies (which ones?) that the Trophon EPR is not indicated to high-level disinfect. This clarification is an important labeling consideration. (For the purpose of this response, I assume that an ultrasound “transducer” is the same as an ultrasound “probe.”)

      (2) For those specific ultrasound transducers and probes that the Trophon EPR is labeled to high-level disinfect, consider requesting confirmation from their manufacturers’ quality assurance departments confirming that the Trophon EPR’s hydrogen peroxide-based disinfectant (at its indicated concentration of 31.5% and minimum chamber temperature of 56o C) and sealed chamber’s fluid pressure will not damage any of the probe’s components or materials.

      The Trophon EPR’s written compatibility with the materials and components of different ultrasound transducers is an important quality-assurance measure with implications that, in addition to its initial cost and cost per cycle, affect the Trophon EPR’s cost-effectiveness. (Refer to this link:

      (3) Understand that, if a facility were to purchase the Trophon EPR, its use would require that the cleaned probe be *dried* prior to high-level disinfection, not remain wet with rinse water prior to processing. Because the probe does not have any internal channels, this is unlikely to be a limitation. The YouTube link, above, suggests that wiping the instrument with a paper towel before disinfection is sufficient (although, this practice could be controversial if such wiping were to re-contaminate the instrument). I would favor wiping the instrument after disinfection *only* if the method does not result in the instrument’s re-contamination (i.e., use a “sterile,” or at least new and clean, wipe).

      (4) The 510(k) clearance of the Trophon EPR states that upon completion of this automated device’s cycle, the disinfected ultrasound transducer is “ready for immediate use.” Therefore, consider clarifying with its manufacturer whether any infection-control practices (e.g., drying the probe using 70% alcohol) might be required, or are permissible, if the probe were not to be used “immediately” after processing but, for example, several minutes later. Namely, does the device’s instructions for use (IFUs) indicate the appropriateness of wiping the instrument with a paper towel to dry it after its reprocessing and prior to its use?

      According to an obvious definition of “immediate,” any delay in its clinical use after processing might require (depending on the manufacturer’s labeling) that the probe be reprocessed, again, in the Trophon EPR before the probe’s reuse. Moreover, as I have published, the use of a wet instrument in the clinical setting can increase the risk of disease transmission. Refer to one of my articles on this topic in the journal “Chest”:

      The definition of “immediate” is a possible source of confusion. Specifically, if the definition of “immediate” were viewed pragmatically, a fair question to ask is the amount of time that would be allowed to elapse after the probe’s processing without violating the device’s definition of “immediate” (e.g., 0 seconds, 1 minute, 5 minutes, up to one hour).

      I pose a question: Would the use of a possibly wet ultrasound probe 10 minutes after its processing be considered, from a pragmatic standpoint, still “immediate” and consistent with the Trophon EPR’s labeling?

      (5) The Trophon EPR is a “disinfector,” not a “washer-disinfector,” and, therefore, this device requires staff to thoroughly perform cleaning (according to the probe’s labeling) prior to automated disinfection. Such manual cleaning is commonplace, however, and not a significant limitation.

      (6) The Trophon EPR is indicated to high-level disinfect the probe, including its shaft and handle. Consider clarifying with the Trophon EPR’s manufacturer whether any other of the probe’s components (e.g., its cable?) require some reprocessing, and, if so, the level of decontamination.

      (7) And, because the Trophon EPR uses vaporized hydrogen peroxide, it appears that the ultrasound transducer – and this a somewhat unique and potentially beneficial feature – does not require water rinsing after exposure to the disinfectant, which presumably would reduce the likelihood of the use of a wet probe and the transmission of environmental, waterborne bacteria via the probe. But wiping the probe with a paper towel after its processing could be a concern if the towel is not clean or is otherwise contaminated.

      Nevertheless, the Trophon EPR’s brochure indicates that small quantities of water vapor (and oxygen) are produced as by-products of the process. Therefore, water may remain on the instrument after its processing, thereby explaining why the Trophon EPR’s labeling requires “immediate” use of the processed probe (and why the YouTube shows the nurse wiping the wet probe to dry it after its processing). Whether the amount of water (as a vapor) remaining on the processed probe is sufficiently significant for an infection-control guideline to recommend drying the probe (facilitated by the use of 70% alcohol) before its clinical use is unclear and something to be clarified. To be sure, wet instruments generally increase the risk of bacterial infections.

      In closing, there are several issues (e.g., those with financial, infection-control, quality-assurance, and both safety and effectiveness implications) that require addressing before purchasing, and when using, any device used to reprocess an ultrasound probe, flexible endoscope, or other type of reusable instrument. Note that I am unaware of the Trophon EPR being associated with any instrument damage, faulty disinfection, inadequate water rinsing, or patient infection or harm. Also, do not hesitate to contact the Trophon’s manufacturer with any additional questions. This manufacturer appears to be committed to quality and patient safety.

      Best regards, Larry

      Lawrence F. Muscarella, Ph.D.
      Independent Infection Prevention Consultant
      P.O. Box 103, Colmar, PA 18915
      Founder of the blog: “Discussions in Infection Control”
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