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Disinfection vs Sterilization: The 4 Levels Explained
Sterilization, high-level, intermediate-level and low-level disinfection: what the CDC says each one actually destroys, in the CDC's own sentences.
The short answer
High-level disinfection is the CDC's definition for eliminating all microorganisms on an instrument except small numbers of bacterial spores. It sits below sterilization, which destroys spores too, and above intermediate- and low-level disinfection. The CDC guideline sets it as the floor for semicritical items such as endoscopes. Read from the CDC on September 5, 2026.
Sterilization describes a process that destroys or eliminates all forms of microbial life and is carried out in health-care facilities by physical or chemical methods.
Disinfection describes a process that eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects
The practical difference is what survives: sterilization leaves nothing, disinfection leaves bacterial spores standing even at its strongest setting.
| Level | What it does | Bacterial spores | Required for |
|---|---|---|---|
| Sterilization | Destroys or eliminates all forms of microbial life. | Destroys them too. Nothing survives, spores included. | Bought sterile or sterilized, with steam where possible. |
| High-level disinfection | Complete elimination of all microorganisms, except small numbers of bacterial spores. | Survive in small numbers. That gap is the entire boundary with sterilization. | High-level disinfection is the floor. |
| Intermediate-level disinfection | Cidal for mycobacteria, vegetative bacteria, most viruses and most fungi; not for spores. | Not addressed. Neither is any guarantee against mycobacteria's tougher relatives. | No Spaulding category's floor. It shows up as the exception inside noncritical, for brief contact with skin that is not intact. |
| Low-level disinfection | Kills most vegetative bacteria, some fungi, and some viruses, in ten minutes or less. | Not addressed, and neither are mycobacteria. This is the floor, not a margin. | Low-level disinfection. |
Each level, in the CDC's own sentence
Every row above is a paraphrase. Here is the exact sentence behind each one, so nothing here rests on a summary of a summary.
Sterilization
Sterilization describes a process that destroys or eliminates all forms of microbial life and is carried out in health-care facilities by physical or chemical methods.
CDC, Guideline for Disinfection and Sterilization in Healthcare Facilities (2008), Introduction, Methods, and Definition of Terms, read .
Most of the items in this category should be purchased as sterile or be sterilized with steam if possible.
CDC, Guideline for Disinfection and Sterilization in Healthcare Facilities (2008), A rational approach to disinfection and sterilization.
High-level disinfection
High-level disinfection traditionally is defined as complete elimination of all microorganisms in or on an instrument, except for small numbers of bacterial spores.
CDC, Guideline for Disinfection and Sterilization in Healthcare Facilities (2008), A rational approach to disinfection and sterilization, read .
Semicritical items minimally require high-level disinfection using chemical disinfectants.
CDC, Guideline for Disinfection and Sterilization in Healthcare Facilities (2008), A rational approach to disinfection and sterilization.
Intermediate-level disinfection
Intermediate-level disinfectants might be cidal for mycobacteria, vegetative bacteria, most viruses, and most fungi but do not necessarily kill bacterial spores.
CDC, Guideline for Disinfection and Sterilization in Healthcare Facilities (2008), Introduction, Methods, and Definition of Terms, read .
Some items that may come in contact with nonintact skin for a brief period of time (i.e., hydrotherapy tanks, bed side rails) are usually considered noncritical surfaces and are disinfected with intermediate-level disinfectants
CDC, Guideline for Disinfection and Sterilization in Healthcare Facilities (2008), A rational approach to disinfection and sterilization.
Low-level disinfection
Low-level disinfectants can kill most vegetative bacteria, some fungi, and some viruses in a practical period of time (≤10 minutes).
CDC, Guideline for Disinfection and Sterilization in Healthcare Facilities (2008), Introduction, Methods, and Definition of Terms, read .
Table 1 lists several low-level disinfectants that may be used for noncritical items.
CDC, Guideline for Disinfection and Sterilization in Healthcare Facilities (2008), A rational approach to disinfection and sterilization.
High-level disinfection vs sterilization: the boundary
High-level disinfection traditionally is defined as complete elimination of all microorganisms in or on an instrument, except for small numbers of bacterial spores.
That surviving margin, small numbers of spores, is the entire gap between the two. It is also why a critical item, one entering sterile tissue or the vascular system, can never be processed with high-level disinfection alone: the guideline requires it be sterile, and spores surviving is the definition of not sterile.
Four processing levels, three Spaulding categories
The Spaulding scheme sorts devices into critical, semicritical and noncritical items, and each of those has its own floor: sterilization, high-level disinfection and low-level disinfection. Intermediate-level disinfection is not any category's floor. Some items that may come in contact with nonintact skin for a brief period of time (i.e., hydrotherapy tanks, bed side rails) are usually considered noncritical surfaces and are disinfected with intermediate-level disinfectants
See the classification in action
Sort twenty real devices into the three Spaulding categories and read the CDC sentence behind each answer. Free, no account.
Questions people ask
What is the difference between disinfection and sterilization?
Sterilization destroys or eliminates all forms of microbial life, bacterial spores included. Disinfection eliminates many or all pathogenic microorganisms, but even its highest level leaves small numbers of spores behind. The CDC treats them as two different endpoints, not two strengths of the same process.
What are the levels of disinfection?
Three, from strongest to weakest: high-level, intermediate-level and low-level. Sterilization sits above all three. High-level disinfection is the CDC's floor for semicritical items such as endoscopes, intermediate-level is cidal for mycobacteria and most viruses and fungi but not spores, and low-level handles vegetative bacteria and some fungi and viruses on surfaces that only touch intact skin.
What are examples of high-level disinfection?
The CDC's own list for semicritical items: This category includes respiratory therapy and anesthesia equipment, some endoscopes, laryngoscope blades, esophageal manometry probes, cystoscopes, anorectal manometry catheters, and diaphragm fitting rings. Any of these gets at least high-level disinfection, or sterilization where feasible.
What are examples of low-level disinfection?
The CDC's list for noncritical patient care items: Examples of noncritical patient-care items are bedpans, blood pressure cuffs, crutches and computers. These touch intact skin only, so low-level disinfection is the CDC's floor for them.
Is high-level disinfection the same as sterilization?
No. High-level disinfection is traditionally defined as complete elimination of all microorganisms except for small numbers of bacterial spores. That surviving margin, however small, is the entire boundary: sterilization leaves none.
What is peracetic acid sterilization used for?
However, reprocessing heat- and moisture-sensitive items requires use of a low-temperature sterilization technology (e.g., ethylene oxide, hydrogen peroxide gas plasma, peracetic acid). Peracetic acid is one of the low-temperature options for instruments that cannot tolerate a steam cycle.
Why are there four processing levels but only three Spaulding categories?
Because intermediate-level disinfection is not any category's floor. Critical items need sterilization, semicritical items need high-level disinfection, and noncritical items need low-level disinfection. Intermediate-level shows up only as an exception inside noncritical, for surfaces with brief contact with skin that is not intact, such as a hydrotherapy tank.