Decontamination, Disinfection & Sterilization: What You Need to Know

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Written by: Scott Mechler

BS Mechanical Engineering, Mechanical Engineer

Written by Scott Mechler with Support from Amit Gupta.

With news relating to the COVID-19 pandemic reaching a fever pitch, there’s been increased attention on what we as individuals and organizations can do to prevent transmitting the virus, which can last on surfaces anywhere from several hours to several days. As a result, deep-cleaning services are experiencing record business, called in to treat offices, campuses and businesses that confirmed coronavirus patients are known to have visited.

Terminology related to these procedures is being used more colloquially now than ever before, which muddies the precise meaning of various terms, such as disinfection, sterilization, decontamination and cleaning, each of which have different definitions and different applications. Various agencies such as the NIH, the CDC, the FDA, the EPA and the WHO each have their own similar, yet distinctly different definitions for these terms, which adds to the confusion.

In order to understand exactly what it is you require for your application, it’s important that you take time to learn the precise meaning of these terms.


Decontamination is a general term that can be applied to any process that reduces pathogens on an object or area known to be contaminated. Decontamination is not a precise term and does require the reduction of pathogens by a certain value. Furthermore, decontamination may be used in relation to dirt/soil, pathogens, radiation, and/or any other form of contaminant. Processes used to achieve decontamination can range anywhere from ordinary soap and water to sterilization with a steam autoclave. Decontamination can, but does not necessarily, mean that all forms of potentially harmful sources have been neutralized. Both disinfection and sterilization are considered forms of decontamination.


The CDC defines cleaning as, “the removal of visible soil (e.g., organic and inorganic material) from objects and surfaces and normally is accomplished manually or mechanically using water with detergents or enzymatic products.”

Note that, in medical terminology, “soil” does not refer to dirt you might find on the ground but rather any visible contaminant (e.g. blood, mucus, etc.) that might be left on a medial device.

The important distinction between cleaning and any other treatment, which are generally referred to as decontamination, is that cleaning says nothing about microorganisms or any other contaminant invisible to the naked eye. A surface can be “clean,” but still potentially contaminated by coronavirus, bacteria or other pathogens. Since the presence of dirt and organic material reduces the efficacy of disinfection or sterilization by trapping harmful microbes, cleaning processes are typically used as a pre-treatment to reduce these physical barriers prior to operations that address the microscopic contaminants.


The EPA defines sanitizing as:

“…the use of a chemical product or device (like a dishwasher or a steam mop) that reduces the number of germs on surfaces or objects to a level considered safe by public health standards or requirements.”

For example, in food service, a sanitizer should reduce the number of germs on a hard surface by 99.999% within 30 seconds. Outside of food service, hard surface sanitizer standards can be found in ASTM E1153 or referenced in EPA 810.2100 guidelines, which require a >99.9% reduction within five minutes. Sanitizing is similar to cleaning in that it renders an object or area safer, but not necessarily safe. Like cleaning, sanitizing is often used in healthcare-related industries as a pre-treatment for further processing, such as disinfection or sterilization.


The FDA defines disinfection as:

“…the destruction of pathogenic and other kinds of microorganisms by physical or chemical means. Disinfection is a less lethal process than sterilization, since it destroys most recognized pathogenic microorganisms, but not necessarily all microbial forms, such as bacterial spores.”

Bacterial spores are a major point in the distinction between disinfection and sterilization. Viruses do not reproduce via spores, which is one of many reasons why efforts surrounding the novel coronavirus are centered around disinfection. The NIH calls out this distinction specifically, saying “Both disinfection and sterilization remove pathogens. The key to distinguishing the two techniques is the endospore.”

The CDC categorizes disinfection as high, intermediate and low-level disinfection based on the types of organism destroyed at each level. Sterilization is the highest level and refers to the destruction of all potentially pathogenic organisms.

Like all coronaviruses, SARS-CoV-2 falls under the subset of a lipid virus. Lipid viruses are a single strand of RNA enveloped and preserved within a membrane of fat. Most chemicals rated as disinfectants can destroy this envelope and cause the RNA to break down, making lipid-enveloped viruses among the easiest microorganisms to inactivate.

Intermediate disinfection refers to any procedure that also successfully destroys fungi and vegetative microorganisms, most notably mycobacterium tuberculosis, the organism that causes the disease of the same name in humans. Chemical disinfectants rated for this level often share the label “tuberculocidal.”

Finally, high-level disinfection refers to any procedure that destroys all microorganisms aside from large concentrations of bacterial spores. Typically, high-level disinfection is performed using an EPA-approved disinfectant chemical.


Unlike disinfection, the definition for sterilization is more straightforward. Sterilization refers to the process by which all microorganisms, including bacterial spores, on an object or surface up to a prescribed level are destroyed. The “prescribed level” is determined through a validation process that uses a biological indicator containing non-infectious bacterial spores. The spore Geobacillus stearothermophilus is commonly used to validate sterilization because it is known to be among the most difficult to inactivate. The biological indicator will contain a known population of these spores — for example, 1,000,000 spores. A sterilization process is deemed successful if it is able to kill all of these spores.

A common misconception is that sterilization is binary — that is, that an object is either stable or not. In reality, sterilization is a statistical event; one can only be sure of sterility up to a certain point. The confidence factor is expressed as a probability metric called Sterility Assurance Level (SAL). SAL is written in the form 10-n, most commonly 10-6, which is a 1/1,000,000 chance of a single microorganism having survived the sterilization process. This is also referred to as a “6 Log” reduction of viable organisms.

By altering the process parameters, the SAL can be modified to meet various requirements. For a steam sterilization process, increasing one or both of the primary parameters — time and temperature — would increase SAL. While an SAL of 10-6 is most common, processes that require a higher confidence in sterility may employ an “overkill” approach. Overkill typically refers to processes that target an SAL of 10-12. The intention of overkill is to reduce the likelihood of viable organisms to a level so low that the risk is essentially zero.

When determining the process parameters for sterilization and validation, it is important to consider the pathogens that may be present and the risk they pose. Historically, the rule of thumb for steam sterilization has been 15 minutes at 250° F based on a 6 Log reduction of bacterial spores. More recently, a new category of disease-causing microorganisms called prions have emerged. Prions have caused widespread concern within the medical community because they are more resistant to common sterilization standards than bacterial spores. As discussed in our blog post on the subject, in order to ensure that acceptable sterility is achieved, it’s important to take special measures if items have been exposed to prions.

Sterilization is the gold standard of microbial decontamination but can only be performed via an approved procedure using a recognized sterilant. While steam is the most widely used sterilant, there are many other available methods that rely on chemicals, radiation and/or phases of matter. Material compatibility typically informs which sterilant is the best selection for an application. Steam is generally the preferred method of sterilization — that is, so long as it’s compatible — because of its low cost, low process time and general acceptance by regulatory agencies.

Spaulding Classification

In the healthcare sector, the requisite level of disinfection or sterilization is organized into a three-tier classification system called the Spaulding Classification. According to this system, instruments are classified as either non-critical, semi-critical or critical. Critical items are those that enter sterile body cavities in patients, such as surgical instruments, catheters, needles or ultrasound probes. These items must be subjected to a sterilization process.

Semi-critical items, such as endoscopes and bandages, come into contact with mucous membranes or non-intact skin and must be subjected to a high-level of disinfection (though sterilization is preferable). Finally, non-critical items are those that only come into contact with intact skin, such as blood pressure cuffs, crutches or general surfaces within a hospital. These must be subjected to low-level disinfection only to kill vegetative bacteria and viruses that could be transmitted through contact.

Generally, the choice to pursue one level of decontamination over another tends to be based on criticality, the likelihood than an instrument or surface could transmit a disease to a patient and the time required to ensure a given level of decontamination. Surfaces, instruments and PPE may not need to be rendered completely sterile to achieve the full inactivation of certain types of microorganism, like SARS-CoV-2, the virus that causes COVID-19. As technology continues to emerge in the fight to preserve stockpiles of critical PPE, it is important for all healthcare workers and support personnel to understand exactly the level of decontamination that is provided by a particular type of process or technology.

These are challenging times, and it is important that we all do our part to stay safe. If you have any questions concerning sterilization procedures, don’t hesitate to contact Consolidated Sterilizer Systems today.

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