Methods of decontamination

Decontamination is a combination of processes that removes or destroys contamination so that infectious agents or other contaminants cannot reach a susceptible site in sufficient quantities to initiate infection, or other harmful response. The various levels of decontamination are described below.

Cleaning is a process that physically removes contamination, including some microorganisms and, if soiling is present, it is an essential step before effective disinfection or sterilisation can be performed. Cleaning does not necessarily destroy all microorganisms, even if a surface looks cleaner. The cleaning of equipment and work surfaces is best done using detergent and warm water. It is also important to ensure that the cleaning product used will not damage equipment and work surfaces.

Ultrasonication is a liquid-based method of cleaning recommended for some equipment, and is dependent upon cavitation (rapid formation and collapse of minute bubbles in a liquid). This method is used routinely within healthcare, laboratory, body art and beauty sectors, but is appropriate whenever cleaning of contaminated, reusable items is required. The treated items must be submersible, and ultrasonication is performed in a lidded tank and can even clean apertures and recesses. Ultrasonic cleaners should be cleaned twice a day as a minimum requirement, and kept clean and dry overnight. Choice of cleaning agents should be recommended by the manufacturer and should reflect the planned use.

This aims to reduce the number of microorganisms present to a level that is unlikely to cause infection. For practical purposes, disinfection may destroy or inactivate many or all pathogenic microorganisms, but not spores.

It is important to realise that successful disinfection is very much dependent on the number of microorganisms initially present. Therefore, physical cleaning is an important prerequisite to effective disinfection.

This term is applied to a process of disinfection on tissue. Only disinfecting agents that are not toxic to the tissue may be used as antiseptic agents.

In contrast to disinfection, this is an absolute term denoting destruction of all micro‑organisms, including spores.

Heat treatment is the most effective routine means of destroying the infectivity of all microorganisms, including BBV, and mainly involves the use of autoclaves (pressure steam sterilisers). Boiling and dry heat ovens do achieve raised temperatures that can kill microorganisms, but they may lack the required level of heat delivery and treatment control offered by steam sterilisers, and so are less reliable. There is also evidence that dry heat and boiling systems are seldom maintained or not subjected to periodic testing, necessary to ensure that they are achieving sterilizing conditions consistently.

Medicines and Healthcare Products Regulatory Agency Safety Notice SN 2002(02) - Dry heat (hot air) sterilizers..

Steam sterilisation (ie vacuum steam autoclaving), is the preferred method of sterilising equipment as it is quick, automated, easy to use, reliable, non-toxic and always effective when used correctly. It is particularly suitable for reusable, heat-stable items, so long as these parts are already physically clean. All BBV are susceptible to standard autoclave treatments with pressurised steam, and large and small steam sterilisers are available, as is guidance on their use and maintenance.

Bench-top steam sterilizers - guidance on purchase, operation and maintenance: Medical Devices Agency, Device Bulletin 2002(06) October 2002. .

When autoclaving is impractical, small heat-stable items may be disinfected using hot water treatments. The MHRA Microbiology Advisory Committee to Department of Health no longer recommends simple immersion of items in boiling water as sufficient for sterilisation. Thermal washer-disinfectors are acceptable and use a combination of physical cleaning and thermal biocidal action to achieve disinfection of contaminated, reusable items. This approach can either be used prior to reuse or to make items safe to handle before further reprocessing.

Sterilization, disinfection and cleaning of medical equipment. The MAC Manual Part I, 2002 edition, Medicines and Healthcare Products Regulatory Agency (MHRA) Microbiology Advisory Committee to Department of Health. .

Dry heat sterilisers offer another method of sterilisation, which is effective provided that the steriliser has an automatic controller that will ensure that appropriate temperatures are achieved throughout the load. Temperatures must be maintained for the duration of the sterilising time and required conditions are as follows:

As well as the strict controls required for this method, dry heat sterilisation time is long and additional time is required for the items to cool to room temperature prior to use. Items must be able to withstand at least 160°C for long periods. Further information on dry heat sterilisers and their use is available from MHRA.

Medicines and Healthcare Products Regulatory Agency Safety Notice SN 2002(02) - Dry heat (hot air) sterilisers.

Some chemical disinfectants have been tested for their activity against BBV in the presence of whole blood or plasma (the fluid component of blood) in order to simulate in-use conditions. The protein in blood and other body fluids may confer a protective effect for the virus, and in some cases may reduce the efficacy of chemical disinfectants. Effective testing of disinfectant can therefore be challenging, but it is reasonable to assume that - because of its robustness - any preparation effective against HBV, will also be effective against other blood-borne viruses.

Disinfection of contaminated surfaces with bleach solution (minimum 1000 ppm active chlorine) is known to be effective for the inactivation of BBV, but bleach is also susceptible to inactivation by organic soiling. Indeed, when disinfecting any soiled item, this underlines the need for prior cleaning in order to reduce the organic load and thus promote adequate disinfection. This should not be done manually if operator safety is compromised, but may be achievable by alternative means in such cases, eg use of an ultrasonication tank, washer disinfector. Surface decontamination using liquid vacuum methods, eg of floor, carpets and upholstery surfaces, would be acceptable only if liquid disinfectant were present in the bulk cleaning fluid. The disinfectant would have to be compatible with the vacuum equipment, any co-added detergent and the treated materials themselves.

Additional free information on chemicals and their safe use is available under COSHH.

All chemical disinfectants have their limitations and appropriate uses, and reliable inactivation of infectivity is difficult to achieve under some conditions. The presence of blood, body fluids and other organic matter can markedly reduce their action.

All disinfectants are potentially hazardous and must be stored and used with caution; hypochlorite for example, corrodes metals, irritates skin and bleaches fabrics and clothing. An assessment of products in use should form part of the assessment of risk from hazardous substances required under COSHH.

Key points to consider in the use of disinfectants are:

The following Health Technical Memoranda (HTM 01 sub-divisions) are either available or pending for the various areas indicated. Additional information on many of these is available via the Central Sterilising Club or via the Department of Health on their decontamination update web pages "NHS Decontamination Programme - Latest news".

Blood and body fluids may contain a high concentration of microorganisms from known BBV-infected individuals. If spills are large, eg from deep cuts, they are a source of potential infection for others who may come in to contact with the spill. All spills should therefore be made safe as soon as possible after the spillage is discovered. Because clearing blood or body fluid spillages may expose an individual to infectious microorganisms, every care must be taken to ensure the member of staff is protected by the appropriate use of protective clothing. Local codes of practice should specify procedures (eg spill kits) and the disinfectants to be used for dealing with spillage and other forms of contamination.

The following points apply, regardless of the scale of the spill:

In an environment where there are likely to be blood or body fluid spills, carpets and soft furnishings should be avoided, as they will be damaged by most chemical disinfectants suitable for routine use. Washable chair covers should be considered if necessary. Within the domestic environment it is, however, unlikely that such measures will be in place. Sensible options must therefore exist for cleaning and disinfecting soft furnishings following spillage of body fluids.

If contamination does occur, eg of carpets or other fixed cover textiles, detergent cleaning should be followed by steam cleaning, so long as the materials will tolerate this. For curtains and other loose cover items, laundering or dry-cleaning followed by hot pressing is effective. Again, textiles should be checked to ensure their tolerance of such treatments. It should, however, be noted that the efficacy of such procedures is likely to be variable, and dependent on choice of (steaming) equipment, disinfectants and nature of the textile being treated.

If unable to disinfect as suggested, it will be necessary to incinerate soft furnishings if the contamination level is heavy and if there are grounds for believing that the contaminating material is infectious.

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