Disinfection is a process that reduces the number of microbes on a reusable medical device, but it does not necessarily destroy certain viruses and bacterial spores. It is not generally as effective as sterilisation in reducing microbial contamination.

We normally use disinfection to decontaminate medical devices that are not intentionally invasive but are in contact with mucous membranes, blood, body fluids and other potentially infectious material (i.e. medium-risk items). Although not the preferred option, in some circumstances you can use disinfection to decontaminate high-risk items, if no practical means of sterilisation is available, e.g. for heat sensitive items.

Cleaning is an essential first step in preparing all reusable medical devices for disinfection (refer to Cleaning). You can disinfect devices by using a washer-disinfector, using low-temperature steam, or by immersion in a liquid disinfectant. If you can, use heat disinfection rather than chemical disinfectants. Only use chemical disinfectants for decontaminating heat sensitive medical devices when alternative methods are not available or appropriate. Methods of disinfection are fully described by the Medical Devices Agency (www.medical-devices.gov.uk/mda )⁴.

Using a washer-disinfector provides cleaning as well as disinfection of the medical device. Thermal disinfection is the preferred method. However, chemical disinfection may be necessary for heat sensitive devices. Refer to Thermal washer-disinfectors and Chemical washer-disinfectors for further information.

Low-temperature steam disinfection is an automated physical process that you can use to disinfect reusable medical devices, provided the conditions of the process will not damage the device. The process works by removing air and exposing every surface of the device to saturated steam, below atmospheric pressure, at 73 °C for ten minutes. Sealed, oily or greasy items and those that retain air are not suitable for low-temperature steam disinfection.

The machine must be capable of reproducible and recordable performance to specified parameters. Machine and processing faults should be automatically detected and signalled and the process stopped. Machine faults require immediate investigation and correction by skilled engineers, including the manufacturer if necessary. You must follow the manufacturer’s instructions for operation, testing and maintenance. Only trained staff should operate the machine. On completion of the process, you must complete any necessary documentation to record that you have disinfected the medical device and the method you used.

You must only use liquid disinfectant immersion for disinfecting reusable heat sensitive medical devices when alternative methods are not available or appropriate. A chemical disinfectant is a compound that under defined conditions is capable of destroying microbes by chemical or physicochemical means. Disinfectants vary in their properties and range of microbial activity, which means that it is very important to choose the correct disinfectant for each specific task. This will depend on the type and amount of soiling and the compatibility of the device with the disinfectant (always refer to the manufacturer’s instructions). The process is only effective if you clean the device thoroughly, choose the correct disinfectant, use it at the specified concentration, and achieve good contact between the disinfectant and the device for the specified minimum time. Refer to Disinfectants for further information on the properties and use of chemical disinfectants.

Methods of chemical disinfection are fully described by the Medical Devices Agency (www.medical-devices.gov.uk/mda)⁴. Only staff who are trained to carry out chemical disinfection should do so. The procedure includes the following steps.

• Wearing appropriate personal protective equipment, fill a suitable receptacle (the receptacle should have a lid and be large enough to fully immerse the device) with sufficient disinfectant solution (prepared according to the manufacturer’s instructions) to allow complete immersion of the device.
• Fully immerse the cleaned medical device in the solution taking care to displace any trapped air.
• Use an irrigation device if necessary, to ensure that the disinfectant reaches all surfaces of the medical device.
• Place the lid on the receptacle and leave it for the specified time.
• Lift the device up and allow any excess disinfectant to drain into the receptacle.
• Transfer the device to a clean rinsing receptacle and rinse it thoroughly with water of suitable microbiological quality to remove all traces of the disinfectant.
• Remove the device from the rinse water, drain off any excess water and carefully dry all the surfaces of the device using a disposable absorbent non-shedding cloth, an industrial hot air dryer, or by placing the device in a drying cabinet.
• Thoroughly wash, dry and disinfect or sterilise the receptacles (as appropriate) and store them dry in a clean area.
• Remove personal protective equipment and decontaminate your hands.
• Complete any necessary documentation to record that you have disinfected the device and the method and solutions you used.

Chemical disinfectants can irritate the skin, eyes and respiratory tract. Some are also corrosive, volatile and flammable. Before using any disinfectant, you must undertake a risk assessment⁸.

There are numerous disinfectants available that you can use for liquid disinfectant immersion. The manufacturer may supply these ready for use or you may need to mix them with an activator or accurately dilute them with water to an appropriate strength immediately before use.

Disinfectants vary in their properties, so it is important to choose the correct disinfectant for a specific task. Most chemical disinfectants are capable of eliminating gram positive and gram negative bacteria and enveloped viruses. A few may be capable of destroying non-enveloped viruses, mycobacteria, protozoan cysts or bacterial spores. The required contact time varies with each disinfectant. However, disinfectants destroy most viruses and non-sporing bacteria within ten minutes. Disinfectants used to destroy mycobacteria and spores can take several hours to work. The choice of disinfectant will also depend on the type of soiling and the compatibility of the disinfectant with the particular medical device. Incompatibility of a disinfectant can result in damage to the device. Therefore, you should always refer to the manufacturer’s advice before exposing a device to a chemical disinfectant.

Successful disinfection requires:

• a chemical with appropriate antimicrobial properties
• a chemical that is of the appropriate dilution and strength (according to the manufacturer’s instructions)
• a chemical that is stable
• a chemical which is compatible with the item to be processed
• close contact between the disinfectant and the device
• processing for a predetermined minimum time (according to the manufacturer’s instructions).

Your local disinfection policy, produced in consultation with your Infection Control Team, should specify the chemical disinfectants that you can use. A careful appraisal is necessary to choose the disinfectant and the process that meets local requirements. You should only make deviations from your local policy following consultation with your Infection Control Team.

You must adhere to the manufacturer’s instructions for using each disinfectant. The following general points apply.

• Always wear appropriate personal protective equipment when using chemical disinfectants.
• Check that each item is thoroughly clean prior to disinfection.
• Check the manufacturer’s instructions for the correct dilution strength, use-by date and period of chemical activity.
• Never mix disinfectants with each other or with other chemicals.
• Remove spills of chemical disinfectants promptly.
• Do not store for longer than advised (disinfectants deteriorate after dilution).
• Ensure adequate ventilation when using disinfectants, especially when using large amounts.
• Always store chemical disinfectants safely.

The Medical Devices Agency provides a summary of the properties of instrument and equipment disinfectants⁴. The information below provides some brief pointers.

Gluteraldehyde 2%

Gluteraldehyde 2% has a broad range of microbial activity even under moderate soiling conditions. It is no longer commonly used in clinical practice. Its use is strictly controlled under COSHH Regulations⁸. The Health and Safety Executive has set maximum exposure limits for gluteraldehyde⁹. This is generally now being withdrawn due to adverse affects on the health of staff.

Ortho-phthalaldehyde (Cidex OPA)

Cidex OPA is a high-level disinfectant with reduced exposure time. It requires no activation and is a clear, pale-blue liquid which contains 0.55% OPA. It has a broad range of microbial activity and requires shorter exposure times than gluteraldehyde¹⁰. It can be an irritant, which may affect the skin, eyes, throat and lungs of health workers who come into contact with it and as such should be used under COSHH Regulations⁸. A Medical Device Alert was issued in 2004 about the risk of hypersensitivity in some patients with a history of bladder cancer having repeated cystoscopy where urological instruments have been reprocessed using Cidex OPA¹¹.

Peracetic acid 0.2 to 0.35%

Peracetic acid is a useful alternative to gluteraldehyde as it is less toxic. It also has a broad range of microbial activity even under moderate soiling conditions. However, it is not as stable as gluteraldehyde and it may be slightly corrosive or damaging.

Alcohol

Alcohol, usually in the form of 70% isopropyl alcohol or 60 to 80% ethyl alcohol (ethanol), is available as a liquid or impregnated into alcohol wipes or swabs. Alcohol is rapidly active against most bacteria and viruses, but it is not sporicidal and has poor penetration. Therefore, its main use is for rapidly disinfecting clean surfaces (e.g. dressing trolleys, scissors) and for wiping over electrical equipment that you cannot clean by immersion methods. The alcohol evaporates quickly to leave surfaces dry. As alcohol is flammable, you cannot use it in large amounts (e.g. in a chemical washer-disinfector).

Peroxygen compounds

Peroxygen compounds have no sporicidal activity and have poor activity against mycobacteria. They are non-irritant at in-use concentrations. However, they are corrosive to some metals. You should only consider using these compounds where the risk of infection from tolerant organisms is low.

Chlorine releasing agents (> 1000 ppm available chlorine)

Chlorine releasing agents have a broad range of antimicrobial activity. The most commonly used agents are sodium hypochlorite (NaOCl) and sodium dichlorisocyanurate (NaDCC). They are useful in decontaminating blood and body fluid spills and have a wide range of environmental applications (e.g. disinfecting worktops, patient supports, mattresses, heat labile linen, baths, toilets and sinks). However, hypochlorite can damage and bleach many fabrics and causes pitting of metal. Organic matter inactivates chlorine releasing agents, so high concentrations are required for direct application to spills or grossly contaminated surfaces. Tablet forms have a longer shelf life than liquid formats. Dilutions of chlorine releasing agents are unstable (they become ineffective within 24 hours), so you must always use a freshly prepared solution. You must not mix these agents with hot water, acids or urine, as a rapid release of irritating chlorine may occur.

Clear soluble phenolics 0.6 to 2%

Clear soluble phenolics have no sporicidal activity and no activity against non-enveloped viruses. Activity against enveloped viruses is poor. However, they are active against bacteria, even in the presence of moderate soiling. You can use them for general environmental disinfection and for disinfecting body fluid spills (particularly faeces and sputum). They are not suitable for clearing blood spills due to their poor viricidal activity.

Quaternary ammonium compounds

The antimicrobial activity of quaternary ammonium compounds varies with the concentration of the product. However, they generally have poor antimicrobial activity and organic matter inactivates them. You should only consider using these compounds where the risk of infection from tolerant organisms is low.

Chlorine dioxide

Chlorine dioxide has similar properties to peracetic acid. It has a broad spectrum of activity and is rapidly sporicidal and is active against non-sporing bacteria, including mycobacteria and viruses at 150 and 350ppm. It is potentially corrosive but commercial preparations contain an inhibitor^12-14.

Superoxidised water

Superoxidised water is generated at the point of use and is the product of the electrolysis of salt solution (NaCl). The solution collected from the anode or positive terminal, contains a mixture of radicals with strong oxidising properties. It is highly effective as a disinfectant and rapidly destroys spores, mycobacteria, fungi and viruses¹⁴. The user hires the disinfector, which is placed close to the endoscope washer-disinfector. The generator criteria are critical to efficacy and are microprocessor controlled and if not met, generation will stop.