Disinfection and Cleaning Methods

All disinfection processes aim to reduce the microbial load of a processed item. How effectively this goal is achieved is defined into one of three levels: high, intermediate or low.

High-level disinfection (HLD)

The goal of this type of process is to kill all but the most resistant of spores. Depending on the item to be processed either heat or liquid immersion techniques can be used.

For a liquid immersion technique to be successful, objects must be completely immersed in a verified high-level disinfectant solution for a predetermined period of time. For example, 0.2% glutaraldehyde solution can be used for up to 45 minutes or 0.2% peracetic acid solution can be used for 12 minutes. It is important to note that long contact times between metal objects and acidic solutions can cause corrosion.

Heat processing for high-level disinfection is known as pasteurization.

Intermediate level disinfection (ILD)

At this level, most bacteria and fungi are inactivated including slow-growing Mycobacterium tuberculosis. However, some infectious spores may remain after processing.

Bleach and alcohols are two examples of intermediate (occasionally low) level disinfectants. There are two main types of bleach; oxygen-based bleaches use hydrogen peroxide as their main active ingredient, while Chlorine-based ones rely on chlorine liberating compound like sodium hypochlorite to do the cleaning. Combining the two can result in large volumes of chlorine gas being quickly released. In a small enclosed space like a bathroom, this can kill a person! This is why people are advised not to mix cleaning products.

Low-level disinfection (LLD)

This is the most basic form of disinfection and is sometimes referred to as sanitization. While many bacteria are inactivated by such processing, M. tuberculosis may survive as may some fungi and spores.

Basic cleaning

At its most basic, cleaning is the simple removal of surface soil and debris from an object (like doing the washing up!). Surface soil can impede the ingress of steam or chemical sterilants, making sterilization processes ineffective. As such, Simple cleaning serves as the foundation for all other decontamination processes. Washing items in water and detergent can be a simple and effective technique. Using enzymes also means a lower temperature can be used during disinfection.

The presence of enzymes in biological detergents is why washing up gloves are important; over a lifetime of exposure, the enzymes in biological dish soap can wreak havoc on your skin!

The utility of some common disinfectants is summarized below:

Table with 7 rows and three columns named: “Agent”, “Disinfection level”, and “Comment”. First agent, glutaraldehyde, has a high disinfection level, needs 0.2% concentration for H L D, can irreversibly bind proteins to the surface of processed objects, and can irritate skin and mucous membranes. Second agent, peracetic acid, has high to intermediate disinfection level, needs 0.2% concentration for H L D, can cause corrosion of metal objects, and produce environmentally safe waste after processing. Third agent, bleach, has intermediate to low disinfection level, needs 10% concentration, comes with two types: “chlorine” and “peroxide”, can corrode metal objects, and can irritate skin and mucous membranes. Fourth agent, alcohol, has intermediate disinfection level, is used on hard surfaces or on the skin, needs above 70% concentration, and denatures cell membranes and dehydrates cells. Fifth agent, iodophor, has low disinfection level, contains iodine, needs 0.1% concentration, and can be used as an antiseptic agent. Last agent, detergent, has a basic disinfection level, can be biological or non-biological, and is used to remove soil and surface debris from items.