. 2016 Oct 14:32–33. doi: 10.1016/B978-0-443-07367-0.00016-1
Stephen NJ Korsman
1,2,3, Gert U van Zyl
4,5, Louise Nutt
6, Monique I Andersson
7, Wolfgang Preiser
8
PMCID: PMC7173467
Introduction
Sterilisation and disinfection are important practices in the clinical and laboratory setting where viruses can be transmitted to humans. Surgical instruments, for example, should not be contaminated with pathogens when they are used in a procedure; similarly, the area to be cut open should be as clean as possible, and not contaminated with organisms.
Definitions
Sterilisation: the complete destruction of all viable microorganisms from a surface, including endospores.
See AlsoStandards for aseptic techniques in medical aesthetic practices in the Benelux: Consensus recommendationsTop 7 Techniques For Effective Cleaning and Sterilization of Dental InstrumentsHow Steam Sterilizers Keep Medical Tools Germ-FreeAnalysis of the role of nail polish in the transmission of onychomycosisDisinfection: the killing of microorganisms on a surface to the point where they no longer pose a threat of disease.
Antisepsis: the disinfection of human tissue.
Decontamination: removal of pathogenic organisms in order to allow safe handling.
Infection control
Infection control is an essential safety component of any setting where pathogens are present. In the clinical setting, it includes, for example, the proper use of antiseptics for wound care, clean practices when performing surgery, sterile equipment, safety when handling potentially infectious items such as used needles, and appropriate hand-washing before touching patients. In certain circumstances, protective clothing (Fig. 1) is required and gloves are essential when taking blood. In the laboratory setting, where specific organisms are deliberately cultured, it includes a wide range of methods to prevent transfer of those organisms to the individuals working with them.
Fig. 1.
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Methods
Mechanical
The most basic mechanical method of disinfection is cleaning with soap and water to remove dirt, organic material such as vomitus or blood, and to start the disinfection process. Soap and detergents are able to damage certain cellular and viral membranes. Cleaning an object or surface (Fig. 2) is essential prior to more specific disinfection or sterilisation, which is not fully effective in the presence of dirt and dense organic matter. Ultrasound can be used to remove dirt where detergents and/or scrubbing are not suitable.
Fig. 2.
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Filtration is a means by which large particles are removed from a solution. Depending on the size of the pores in the filter, different sized particles can be retained. Some filters are designed to filter out only gross debris, while some may filter out bacteria but allow viruses to pass through, and some may filter out even viruses when used in series, as in the case of the high-efficiency particulate air (HEPA) filter. Sterilisation of certain liquids by filtration can be achieved with filters in combination with agents that bind certain substances.
Heat
Heat is used in a variety of different ways:
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Autoclaves – these combine heat, steam and pressure to transmit heat energy to organisms in an optimal way in order to kill them. 121°C for at least 15 minutes is a commonly used protocol. This will kill all bacteria, protozoa, fungi and viruses, but will not completely inactivate prions (Fig. 3).
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Dry heat – items are heated to higher temperatures than autoclaves, as dry heat does not transfer energy to organisms as well as autoclaving.
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In laboratories, small items, such as metal loops used to inoculate agar plates with specimens from patients, can be heated until red hot.
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Boiling and cooking are effective for disinfection, but will not provide sterility.
Fig. 3.
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Not everything can be heated – plastics, for instance, will melt (Fig. 4). Certain substances, such as powders, require dry heat, as do certain metals which could oxidise in an autoclave. Incineration is inappropriate for items meant for re-use, and is used to sterilise medical waste prior to discarding it.
Fig. 4.
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Irradiation
X-rays and gamma rays can be used to sterilise objects, and this is often used for the sterilisation of disposable plastic items such as syringes or drip sets. The radiation damages DNA and protein structures in the organisms.
Ultraviolet light is used in TB clinics and biosafety cabinets to sterilise surfaces. In addition to DNA and protein damage, UV light can convert oxygen (O2) to ozone (O3), which is destructive to organisms.
Chemical
Some items are sensitive to chemicals and cannot safely be sterilised in this way (Table 1). It is important to note that most disinfectants are negatively affected by organic material, which should be washed away before disinfecting an item.
Table 1.
Chemicals used for sterilised and disinfection and their properties
| Chemical/chemical group | Description |
|---|---|
| Ethylene oxide | Toxic, flammable. Good for items that cannot be heated. Somewhat time consuming. |
| Ozone | Toxic, unstable, must be made on site. Used for sterilisation and surface disinfection. |
| Aldehydes (formaldehyde CH2O, glutaraldehyde C5H8O2) | Toxic, time consuming for sterilisation. Formaldehyde can be used as a gas or liquid. |
| Hydrogen peroxide (H2O2) | Used for disinfection and antisepsis; can also be used for sterilisation as a liquid or gas (known as gas plasma sterilisation.) |
| Sodium hypochlorite (NaClO) | Mainly used as a disinfectant, at a 1 : 10 dilution of commercial sodium hypochlorite solution, at which it is most active. Active component is hypochlorous acid. Hypobromites also used. Degrades in the presence of organic material. |
| Chlorine | Forms hypochlorous and hypochloric acids in water, which are active components. |
| Iodine | Used in many disinfectants and antiseptics. Lugol's iodine consists of iodine and potassium iodide. |
| Chlorine dioxide (ClO2) | Explosive; commonly used as a water disinfectant. |
| Potassium permanganate (KMnO4) | Used for disinfection and as an antiseptic. Has also been used as a topical antifungal/antibacterial agent. |
| Phenol | Also called carbolic acid. Phenols are commonly used in household disinfectants. |
| Quaternary ammonium compounds (QACs) | Benzalkonium chloride (BAC) is the most well-known. Relatively non-toxic and non-corrosive. Is used in hand towels, medical disinfectants. |
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Viruses and disinfection
The ability of an agent to inactivate a virus depends on the properties of the agent combined with the properties of the virus (Table 2). In general, viruses with lipid membranes are more labile, and are susceptible to lipid solvents (such as alcohol) and detergents which break up the membrane, whereas those viruses with no membrane are more hardy. The concentration of the agent used also determines its ability to render viruses harmless.
Table 2.
Viruses and agents effective against them
| Virus | Env | Effective agents |
|---|---|---|
| Rabies | + | Heat, soap, non-ionic detergents, iodine, alcohol, hypochlorite, QACs, formaldehyde |
| Ebola/Marburg | + | Lipid solvents, non-ionic detergents, formaldehyde, oxidising agents, heat |
| Paramyxoviruses | + | Lipid solvents, non-ionic detergents, formaldehyde, oxidising agents, QACs, heat |
| Influenza | + | Lipid solvents, non-ionic detergents, formaldehyde, oxidising agents, phenols, QACs, heat |
| Lassa virus | + | Lipid solvents, non-ionic detergents, formaldehyde, oxidising agents |
| Bunyaviruses | + | Lipid solvents, non-ionic detergents, formaldehyde, oxidising agents |
| Enteroviruses | − | Hypochlorite, UV, formaldehyde, phenols |
| Rhinovirus | − | Hypochlorite, UV, formaldehyde, phenols |
| Hepatitis A | − | Hypochlorite, UV, formaldehyde, phenols |
| Hepatitis B | + | Lipid solvents, non-ionic detergents, formaldehyde, oxidising agents, QACs |
| Hepatitis C | + | Lipid solvents, non-ionic detergents, formaldehyde, oxidising agents |
| Rubella | + | Lipid solvents, non-ionic detergents, formalin, heat, pH |
| Herpes viruses | + | Lipid solvents, non-ionic detergents, formaldehyde, oxidising agents, QACs |
| HIV | + | Lipid solvents, non-ionic detergents, formaldehyde, oxidising agents |
| Coronaviruses | + | Lipid solvents, non-ionic detergents, formaldehyde, oxidising agents |
| Adenoviruses | − | Hypochlorite, chlorine |
| Rotavirus | − | Hypochlorite, chlorine |
| Pox viruses | + | Chlorine, hypochlorite, QACs, formaldehyde |
| Papillomaviruses | − | Hypochlorite, chlorine |
| Parvoviruses | − | Formaldehyde, oxidising agents, γ-radiation |
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