What Are High-Level Disinfectants and When Are They Used?

High-level disinfectants are strong liquid chemicals used on reusable medical equipment, one step below full sterilization. They are the standard treatment for things like endoscopes and internal ultrasound probes, which can’t survive the heat used to sterilize surgical tools.1PubMed Central. Guideline for Disinfection and Sterilization in Healthcare Facilities2American Institute of Ultrasound in Medicine. Guidelines for Cleaning and Preparing External- and Internal-Use Ultrasound Transducers and Equipment Between Patients as Well as Safe Handling and Use of Ultrasound Coupling Gel How well they protect depends as much on careful cleaning beforehand as on the chemical itself.

What High-Level Disinfection Kills and What It Doesn’t

Sterilization destroys every microbe, including bacterial spores, the hardiest form some bacteria take.3PubMed Central. Disinfection and Sterilization in Health Care Facilities High-level disinfection destroys all microorganisms except small numbers of those spores.4CDC Guideline for Disinfection and Sterilization in Healthcare Facilities. A Rational Approach to Disinfection and Sterilization Low-level disinfection kills common bacteria and some fungi and viruses, but not tuberculosis germs or spores.5PubMed Central. Disinfection and Sterilization in Health Care Facilities

To earn the label, a product must kill tuberculosis-type bacteria by a factor of a million.6CDC Guideline for Disinfection and Sterilization in Healthcare Facilities. A Rational Approach to Disinfection and Sterilization Those bacteria have waxy walls that resist many chemicals, so they make a practical benchmark. A product that beats them will also handle weaker germs such as common bacteria and most viruses.

The test is run with blood serum added, to mimic a dirty device.7PubMed. Reconciliation of FDA and societal guidelines for endoscope reprocessing A qualifying product therefore works even under poor conditions. Cleaning followed by high-level disinfection should remove enough germs to prevent infection.8CDC Guideline for Disinfection and Sterilization in Healthcare Facilities. A Rational Approach to Disinfection and Sterilization

The few spores that may remain rarely matter on these devices. Spores mainly threaten sterile tissue and the bloodstream, while mucous membranes like the gut lining resist them. That is why leftover spores are an accepted tradeoff for these items.

Which Equipment Gets High-Level Disinfection

Since 1957 hospitals have sorted reusable equipment into three groups by infection risk.9PubMed. A review of Spaulding’s classification system for effective cleaning, disinfection and sterilization of reusable medical devices: Viewed through a modern-day lens that will inform and enable future sustainability10Infection Control & Hospital Epidemiology. Multisociety guidance for sterilization and high-level disinfection Critical items enter sterile tissue, body cavities or blood vessels and must be sterilized, such as surgical instruments.11Infection Control & Hospital Epidemiology. Multisociety guidance for sterilization and high-level disinfection12PubMed. Disinfection, sterilization and antisepsis: An overview Semicritical items touch mucous membranes or broken skin and must be sterilized or high-level disinfected.13Infection Control & Hospital Epidemiology. Multisociety guidance for sterilization and high-level disinfection Noncritical items touch only intact skin, like stethoscopes, and get low-level disinfection.14PubMed. Disinfection, sterilization and antisepsis: An overview

Endoscopes, breathing and anesthesia equipment, and dialysis parts are common semicritical items.15PubMed Central. Guideline for Disinfection and Sterilization in Healthcare Facilities Transvaginal, transrectal and transesophageal ultrasound probes need high-level disinfection before the next patient.16American Institute of Ultrasound in Medicine. Guidelines for Cleaning and Preparing External- and Internal-Use Ultrasound Transducers and Equipment Between Patients as Well as Safe Handling and Use of Ultrasound Coupling Gel Heat sterilization would damage many of these devices, so chemicals are used.17PubMed Central. Guideline for Disinfection and Sterilization in Healthcare Facilities18PubMed Central. New approaches to disinfection of thermolabile medical devices using an indirect method with cold atmospheric plasma-aerosol

A probe is usually covered by a sheath during the exam, but covers can tear or leak unnoticed. The usual order is to remove the cover, wipe off gel and visible matter, apply the disinfectant for the labeled time, and rinse so no residue touches the next patient’s tissue. The probe is then dried and stored so it stays clean.

Experts have proposed moving high-risk scopes such as duodenoscopes up to the critical group.19PubMed. A review of Spaulding’s classification system for effective cleaning, disinfection and sterilization of reusable medical devices: Viewed through a modern-day lens that will inform and enable future sustainability Those scopes would be sterilized at low temperature instead of high-level disinfected, adding a safety margin.20PubMed. A review of Spaulding’s classification system for effective cleaning, disinfection and sterilization of reusable medical devices: Viewed through a modern-day lens that will inform and enable future sustainability A duodenoscope is the scope used for ERCP, a procedure on the bile and pancreas ducts. Its tip has a small moving part that is hard to clean.

The Chemicals Used and How Long They Take

Most need 8 to 45 minutes of contact at room temperature, 20 to 25°C.29PubMed Central. Disinfection and Sterilization in Health Care Facilities A 2% glutaraldehyde solution kills common bacteria in under 2 minutes and tuberculosis germs, fungi and viruses in under 10.30PubMed Central. Guideline for Disinfection and Sterilization in Healthcare Facilities It needs about 3 hours to kill bacterial spores.31PubMed Central. Guideline for Disinfection and Sterilization in Healthcare Facilities

The label’s contact time is counted only once the device is fully submerged and every channel is filled, since trapped air bubbles can leave surfaces unprotected. It assumes the device was cleaned first, because leftover blood or tissue can shield germs. It also assumes the solution is at or above its minimum strength and at the stated temperature, so a cool room or weak solution can mean the time no longer holds. Products differ, so staff follow the label for the specific product and the germs it claims to kill.

The chemicals kill in different ways. Glutaraldehyde binds to germs’ proteins and genetic material, stopping them from functioning.32PubMed Central. Guideline for Disinfection and Sterilization in Healthcare Facilities OPA latches onto proteins on bacterial surfaces and slips through outer layers easily.33PubMed. Studies on the mechanisms of the antibacterial action of ortho-phthalaldehyde In peroxide-peracid mixes, peroxide cracks the spore’s coat and peracetic acid does most of the killing.34PubMed Central. Mechanism of Sporicidal Activity for the Synergistic Combination of Peracetic Acid and Hydrogen Peroxide35PubMed Central. Comparative Evaluation of a Disinfectant Formulation Comprising Hydrogen Peroxide, Peracetic Acid, and Acetic Acid Against Aspergillus niger, Escherichia coli, and Staphylococcus aureus on Various Surfaces in Comparison to Other Disinfectants

Each chemical trades speed, toxicity and gentleness on materials, so one doesn’t fit every device. Device makers specify which products their equipment tolerates, and clinics must follow both the chemical’s and the device’s instructions.

Household bleach isn’t a substitute. High-level products are cleared by regulators for medical devices and come with tested concentrations and soak times. Homemade dilutions lack that testing and can damage devices.

How a Scope Is Reprocessed Between Patients

Reprocessing a gut endoscope rests on manual washing, high-level disinfection and drying.36PubMed Central. High-level disinfection of gastrointestinal endoscope reprocessing Endoscopes are linked to more outbreaks from poor cleaning than any other medical device,37PubMed Central. High-level disinfection of gastrointestinal endoscope reprocessing so skipping or rushing any step undermines the rest.

In practice, staff wipe and flush the scope at the bedside right after use. At a sink, brushes clean the inner channels. The machine or a soak then applies the disinfectant for the labeled time, and the scope is rinsed, dried with air and hung in a cabinet.

Detergent and brushes remove most of the soil and many germs before the soak begins. The brush has to pass through each channel, since a machine’s flow of liquid alone may not dislodge dried material.

Drying matters as much as killing. Moisture left in channels lets surviving germs regrow, and drying lapses have been tied to outbreaks. Dry storage keeps the scope safe until the next use.

An automated endoscope reprocessor is a washer-disinfector machine that runs the disinfection steps the same way each time.38Gastrointestinal Endoscopy. Automated endoscope reprocessors It cuts missed steps and staff contact with fumes.39Gastrointestinal Endoscopy. Automated endoscope reprocessors With these machines, a second round of disinfection didn’t lower contamination where rates were already low.40PubMed. A randomized trial of single versus double high-level disinfection of duodenoscopes and linear echoendoscopes using standard automated reprocessing Still, many facilities in poorer countries disinfect fully by hand.41PubMed. High-level endoscope disinfection processes in emerging economies: financial impact of manual process versus automated endoscope reprocessing

When High-Level Disinfection Fails

A biofilm is a sticky layer that shelters germs from drying and from disinfectants.42PubMed. The role of biofilms in reprocessing medical devices Narrow scope channels make cleaning hard, and biofilm can build up within 30 to 60 days of use.43PubMed Central. How biofilm changes our understanding of cleaning and disinfection One germ in a biofilm survived peracetic acid far stronger than normal use.44PubMed Central. How biofilm changes our understanding of cleaning and disinfection Layers that build over repeated cycles resist disinfectants more than fresh ones.45PubMed Central. Modeling microbial survival in buildup biofilm for complex medical devices

Damage gives germs another place to hide. Scratches, worn coatings and cracks inside a channel are spots where brushes and liquid reach poorly. Wear builds gradually, so a scope that was fine when new may become harder to clean. A visible flaw or a failed leak test means the scope needs repair, not another disinfection cycle, which is why inspection and maintenance are part of reprocessing.

Investigations have found damaged scopes, mishandling and reprocessing errors behind infections.46PubMed Central. The Centers for Disease Control and Prevention Guidance on Flexible Gastrointestinal Endoscopes: Lessons Learned from Outbreaks, Infection Control In one outbreak, 6 of 10 screened patients exposed to one duodenoscope carried a drug-resistant bacterium.47PubMed Central. An update on gastrointestinal endoscopy-associated infections and their contributing factors The scope had not been dried properly.48PubMed Central. An update on gastrointestinal endoscopy-associated infections and their contributing factors The hospitals then prioritized drying and began monthly lab testing of the scope.49PubMed Central. An update on gastrointestinal endoscopy-associated infections and their contributing factors Patients can reasonably ask whether the clinic uses a washer-disinfector machine, whether scopes are dried and stored in cabinets, and whether staff are trained and checked on reprocessing.

How Clinics Check the Disinfectant Is Still Working

Reusable solutions weaken as they are used and diluted. One unit tested its 2.4% glutaraldehyde every morning with test strips, and replaced the solution every 2 weeks, or sooner if it fell below minimum strength.50PubMed Central. Surveillance cultures of samples obtained from biopsy channels and automated endoscope reprocessors after high-level disinfection of gastrointestinal endoscopes Minimum effective concentration is the weakest strength at which the product still works. Such checks matter because reusable solutions often failed strength tests before their maximum use period ended.51PubMed. Challenges in achieving effective high-level disinfection in endoscope reprocessing The failures came from product problems, complex processes and staff not following instructions.52PubMed. Challenges in achieving effective high-level disinfection in endoscope reprocessing

A calendar date isn’t enough, because heavy use can weaken a solution early. Testing before each day’s use catches this, and a failed test means draining and refilling before more devices are processed.

A test strip is dipped into the solution, and its color change shows whether the active chemical is at or above the minimum effective level. Strips have a shelf life too, since an old strip can give a wrong reading. The result is written down, leaving a record that the solution passed before devices were processed.

Health Effects for Staff Who Handle Them

Unprotected exposure can cause skin rashes and breathing symptoms.53PubMed. Occupational health risks associated with the use of germicides in health care All these products irritate skin and airways, but OPA can also cause allergies.54PubMed. Considering risks to healthcare workers from glutaraldehyde alternatives in high-level disinfection Hydrogen peroxide and peracetic acid are not known to trigger allergic reactions in the same way.55PubMed. Considering risks to healthcare workers from glutaraldehyde alternatives in high-level disinfection In one survey of hospital support workers, about 6 in 10 reported skin irritation from OPA.56PubMed Central. Prevalence of Health Effects Due to Disinfectant Exposure and Its Impact on Selected Physiological Parameters Among Class D Workers: A Descriptive Cross-Sectional Study

Vapors matter more than splashes for daily exposure. Some products give off fumes that staff can breathe in when soaking trays are open, irritating the nose, throat and lungs. Keeping lids on tanks and working in a ventilated room cuts the vapor in the air. Splashes to the eyes can cause serious irritation, so eye protection is used when pouring or transferring liquids.

Closed containers, good ventilation and gloves reduce exposure.57PubMed. Occupational health risks associated with the use of germicides in health care Washer-disinfector machines further limit contact.58Gastrointestinal Endoscopy. Automated endoscope reprocessors These risks fall mainly on the people handling the concentrated liquid. Patients face little chemical risk because devices are rinsed after soaking.

Workers should report a skin rash on the hands or forearms after handling solutions, or a cough, wheeze or runny nose that eases on days off. An allergy can worsen with each exposure, so early reporting matters.

Downsides for Devices and the Environment

An incompatible disinfectant can discolor, make sticky or degrade device materials.59Tristel – New Zealand – EN. Material compatibility and efficacy validation: choosing the right reprocessing products for your medical device Peroxide and peracid products can be hard on materials at effective strengths.60PubMed. A new peroxide-based flexible endoscope-compatible high-level disinfectant Peroxide systems can corrode and need longer exposure.61PubMed Central. New approaches to disinfection of thermolabile medical devices using an indirect method with cold atmospheric plasma-aerosol

Makers test their scopes and probes with certain products and list the ones that are safe for their materials. Using an unlisted product can void a warranty and damage the device in ways that aren’t obvious at first. That is why facilities check the compatibility list before they change products.

Chlorine disinfectants form chlorinated by-products in hospital wastewater.62PubMed. Toxicological effects of disinfections using sodium hypochlorite on aquatic organisms and its contribution to AOX formation in hospital wastewater These are very toxic to fish and algae and persist in the environment.63Journal of Global Health Reports. Time to rethink medical disinfection from a planetary health perspective64PubMed. Toxicological effects of disinfections using sodium hypochlorite on aquatic organisms and its contribution to AOX formation in hospital wastewater

Alternatives are being explored. UV light can miss crevices and folds on probes, and cold plasma mists are being tested to reach those areas. None yet replaces approved liquid disinfectants in routine use.