Decontamination is the process of removing or reducing pathogenic microorganisms from a surface or item to a level safe for public health or reuse. Public health standards recognize three primary, hierarchical levels based on the degree of microbial life eliminated. Each ascending level requires a greater kill rate of increasingly resilient microorganisms, moving from simple physical removal to the complete destruction of all life forms.
The Foundational Level: Cleaning and Sanitization
The lowest level of decontamination begins with simple cleaning, which focuses on the physical removal of visible debris, soil, and organic matter like blood or tissue from surfaces. This step is achieved primarily through mechanical action, such as scrubbing, often using water and detergents to lift and suspend the foreign material. Cleaning is a prerequisite for all higher levels of decontamination because organic matter can shield microorganisms, making subsequent chemical processes ineffective.
Sanitization represents a step beyond basic cleaning, applying mild chemicals or heat to further reduce the number of microorganisms to a level considered safe by public health standards. For a product to be labeled a sanitizer, the U.S. Environmental Protection Agency (EPA) often requires it to demonstrate a specific reduction, typically killing at least 99.9% of bacteria. This level is commonly applied to surfaces that contact food in commercial settings or in general household environments.
The Intermediate Level: Disinfection
Disinfection is the intermediate level of decontamination, using chemical agents to kill most vegetative bacteria, fungi, and viruses on inanimate objects. This process is significantly more effective than sanitization, often achieving a 99.999% kill rate of microorganisms. However, a fundamental limitation of disinfection is that it does not reliably kill highly resistant forms of microbial life, specifically bacterial spores.
Disinfection is categorized into three sublevels based on the spectrum of microbes eliminated. Low-level disinfection destroys most vegetative bacteria and some viruses. Intermediate-level disinfection is effective against the bacterium that causes tuberculosis (tubercle bacilli). High-level disinfection (HLD) is the most potent form, killing all microorganisms except for a high number of bacterial spores, and is reserved for items that contact mucous membranes.
The Highest Level: Sterilization
Sterilization is the highest and most rigorous level of decontamination, defined as the complete destruction or elimination of all forms of microbial life. This total microbial kill is quantified by the Sterility Assurance Level (SAL), which is the probability of a single unit remaining non-sterile after processing. The industry standard for items that contact sterile body tissue, such as surgical instruments, is an SAL of \(10^{-6}\) (one in a million chance of containing a viable microorganism).
Sterilization is achieved through various methods, most commonly using physical processes like moist heat under pressure (autoclaving). Chemical methods, including ethylene oxide gas or hydrogen peroxide gas plasma, are used for heat-sensitive items.
Choosing the Right Level of Decontamination
The selection of the appropriate decontamination level is based entirely on a risk assessment tied to the intended use of the item being treated. Items that penetrate sterile tissue or the vascular system, such as surgical instruments, are classified as high risk and must undergo sterilization. Items that contact mucous membranes or non-intact skin, such as flexible endoscopes, are considered medium risk and require at least high-level disinfection (HLD). Conversely, items that only contact intact skin, like stethoscopes or blood pressure cuffs, pose the lowest risk and generally only require cleaning or low-level disinfection.