Criteria for Selecting High-Level Disinfectants (HLD): The Balance Between Spectrum of Activity and Toxicity

The Delicate Balance Between Microbiological Efficacy and Occupational Health

The reprocessing of heat-sensitive (thermolabile) medical devices, flexible endoscopes and surgical optics in healthcare settings is one of the most critical areas of responsibility for infection control committees. For semi-critical medical devices that cannot be sterilised using high-temperature methods such as autoclaving, the high-level disinfection (HLD) process is an essential safety measure. However, the efficacy of a disinfectant cannot be measured solely by its capacity to kill microorganisms.

Selecting an effective high-level disinfectant requires striking a perfect balance between microbiological efficacy and user safety. The greatest dilemma for infection control nurses and laboratory managers is identifying formulations that are powerful enough to eliminate the most resistant pathogens within seconds, yet at the same time will not poison healthcare workers, release toxic vapours into the environment, or corrode sensitive optical components worth millions of lira. In this guide, we detail the scientific criteria for selecting YDDs, the toxicity profiles of active ingredients, and clinical decision-making processes.

I. Spectrum of Activity of YDDs and Pathogen Resistance Hierarchy

According to the Spaulding Classification, all semi-critical devices that come into contact with mucous membranes or compromised skin must undergo at least high-level disinfection. The microbiological performance of a product at this level is in a completely different league to that of standard surface disinfectants.

A. Mycobactericidal and Sporicidal Activity

The groups of microorganisms exhibiting the highest resistance to disinfectants in clinical settings are mycobacteria (Mycobacterium tuberculosis, Mycobacterium terrae) and bacterial spores (Bacillus subtilis, Clostridioides difficile).

The spectrum of activity of disinfectants with mycobactericidal and sporicidal efficacy must include vegetative bacteria, mycobacteria, fungi and enveloped/non-enveloped viruses, as well as bacterial spores. Sporicidal efficacy against bacterial spores must be verified by efficacy tests conducted in accordance with the product’s concentration, contact time and relevant standards.

B. International EN Test Standards and Accreditation

The microbiological claims of the selected product must be verified by tests carried out in independent accredited laboratories. The following European Standards (EN) in particular should be sought for YDD products:

• EN 13727: Assessment of bactericidal activity.
• EN 13624: Evaluation of fungicidal and yeasticidal activity.
• EN 14476: Assessment of virucidal activity.
• EN 14348: Evaluation of mycobactericidal activity.
• EN 17126: Assessment of sporicidal activity.
• EN 14885: Framework standard for chemical disinfectants.

II. Critical Evaluation Matrix for the Selection of High-Level Disinfectants

Infection control nurses and procurement committees should score the following four key criteria when comparing products:

1. Contact Time and Processing Speed: Products that provide full efficacy within 5 to 15 minutes should be preferred to ensure uninterrupted case flow in endoscopy units. A longer duration reduces operational efficiency.
2. Verifiability of MEC (Minimum Effective Concentration): The active ingredient concentration of reusable solutions must be measurable daily using test strips (MEC strips). Products that cannot be verified using these strips are grounds for non-compliance during inspections.
3. Material Compatibility and Corrosion Resistance: The presence of corrosion inhibitors in the formulation prevents damage to the adhesives, optical lenses and polymer coatings of flexible endoscopes.
4. Health and Safety (H&S) Standards: It must be determined whether the product requires a dedicated fume cupboard and whether neutralisation is required for waste management.

III. Detro Healthcare YDD Portfolio: Safe and Approved Solutions

Detro Healthcare offers a range of high-level disinfection products that are fully compliant with international medical device regulations (MDR) and EN standards.

• Detro OPA: With its ready-to-use ortho-phthalaldehyde-based formula, it provides high-level disinfection in 5 minutes. Thanks to its low odour profile and broad material compatibility, it offers maximum safety in the reprocessing of both flexible and rigid endoscopes.
• Detro Forte: A disinfectant that provides a high level of disinfection and sporicidal efficacy thanks to its glutaraldehyde-based formula. Under appropriate conditions of use, it is employed to ensure effective microbiological control during the reprocessing of endoscopes and other reusable medical devices.
• Testing and Traceability: Detro Healthcare products are supported by specialised MEC test strips, which demonstrate the solution’s efficacy within seconds, ensuring full transparency during clinical audits.

Frequently Asked Questions

1. What is the difference between high-level disinfection (HLD) and sterilisation?

Sterilisation is the process of completely eliminating all microorganisms and high numbers of bacterial spores. High-level disinfection, on the other hand, completely eliminates all vegetative bacteria, mycobacteria, fungi and viruses, whilst eliminating only a portion of high numbers of resistant bacterial spores. HLD is considered sufficient and safe for semi-critical devices.

2. Why is a mycobacterial test mandatory when assessing the spectrum of activity of high-level disinfection?

Mycobacteria are the most resistant group of vegetative pathogens to disinfectants due to the rich lipid and waxy layer in their cell walls. It is scientifically accepted that if a disinfectant can kill mycobacteria, it will be able to kill all other standard viruses and bacteria—such as HIV, Hepatitis B/C , and MRSA—much more easily.

3. How does the toxicity of medical disinfectants affect staff health?

Traditional disinfectants with high volatility (e.g. uncontrolled glutaraldehyde) can cause asthma, chronic bronchitis, eye irritation and chemical burns when inhaled in enclosed spaces.

4. Why should the Minimum Effective Concentration (MEC) test be carried out every day?

Every time an instrument is immersed in a reusable YDD bath, water and organic matter are carried into the solution. Over time, this reduces the concentration of the chemical. MEC test strips should be used at the start of each shift or before each procedure to confirm that the solution remains above the active threshold required to kill microbes.

5. Do OPA-based disinfectants stain instruments?

If uncleaned protein residues (blood, mucus) remain on the instrument, OPA reacts with these proteins to form grey-black stains. This is not a fault with the disinfectant, but a visual indication that the instrument has not been adequately pre-cleaned. No staining is observed on instruments that have been thoroughly pre-cleaned.

6. How is material compatibility checked when selecting a YDD?

The product’s technical data sheet and accredited test reports must include tests demonstrating compatibility with stainless steel, aluminium, polymers, rubber and optical adhesives. Formulations containing a corrosion inhibitor should be preferred.