Our vocabulary changes as we learn more. The old words about cleanliness were insufficient - or imprecise - when we want to talked to quantify how clean something needs to be or how much bacteria was on it.

The old words were sanitize, disinfect, and sterilize - in that order of ascending cleanliness. To sanitize means to clean something to the eye. A visual inspection should not reveal substantial dirt or unwanted material. This is how janitors clean toilets and how health inspectors generally evaluate commercial kitchens. To disinfect means to remove pathogens that can cause disease in humans or other mammals. It can only be verified with a scientific test, but industry has generally agreed that cleaning a surface with a liquid or gaseous substance designated a disinfectant counts. That is not foolproof and there can be places where the disinfectant material does not reach but as long as the facility manager makes a good faith effort, the surface or item is considered disinfected.

Bacteria are relatively easy to deactivate. Other pathogens are harder to kill - viruses, some fungi, and particularly bacterial spores which nature has designed to survive extreme conditions. Put a metal medical instrument in a pot of boiling water for a few minutes and you destroy the bacteria, but spores may survive. That’s why even hotter temperatures were required. Sterilization is the eradication of pathogens for all practical purposes. The discovery of prions as a vehicle for disease transmission has complicated things. Like viruses, prions are not really alive in the biological sense, but in the right situation they can reproduce and cause illnesses in their hosts. If all bacteria, bacterial spores, and viruses are eliminated, we call the item sterilized, even though it may contain prions. This issue has come up where surgical instruments that have been sterilized have been found to harbor prions.

Why do we need sterilized items and rooms? For the most part we don’t need sterile rooms. Clean rooms used in some industries have standards for particulate count but microbial populations are usually not measured. A clean room at a semiconductor fab is not sterile.

Is a hospital operating room sterile? No, it is occupied by human beings with bacteria on their skin. (Typical bacteria count is 100 to 10,000 per square centimerer of skin). But the operating team can be reasonably sure the scalpel is sterile.

A person with a normal immune system and no open sores should have no problems with anything that has been disinfected. However, when doctors work inside the patient’s body, they want to use equipment that has been sterilized.

Cleaning in stages has advantages. Disinfection and sterilization processes are never 100 percent effective but you can make them more effective by cleaning superficially first. Get the visible dirt off the object before sterilizing, and the disinfection or sterilization will be more complete.

Who Worries About Cleanliness?

Doctors' offices, veterinarians, dentists, hospitals, and mortuaries all are concerned with cleanliness. Staff at these facilities - janitors, doctors, technicians, etc. - all think about keeping the place clean. Even commonplace cleaning - removing visible dirt - plays a part. This kind of simple cleaning of equipment and facilities before disinfection or sterilization processes are applied can increase the effectiveness of those processes.


Hygienists recognize three levels of disinfection.

  • Low-level disinfection: kills most bacteria, some viruses and fungi.
  • Intermediate-level disinfection: kills or deactivates most viruses and fungi. The well known Mycobacterium tuberculosis bacteria is destroyed.
  • High-level disinfection: destroys all microorganisms (bacteria, fungi) but perhaps not all bacterial spores. Most viruses are deactivated.

Prions are a big mystery. And how much they are affected by disinfection procedures is unknown. Prions do not factor into any guidelines for industrial hygiene or infection control but responsible hygienists and waste managers should keep them in mind.


How do you know if an item or surface or floor has been disinfected or sterilized? Although you could take a sample and examine it for microbes, this is not practical in most cases. Managers usually rely on administrative controls - they keep a history of the item. It’s largely a matter of keeping track of history and knowing what cleaning process has been executed and when the item was cleaned.

Autoclaves are meant to sterilize equipment - lab glassware, scalpels, etc. - and also to render medical waste harmless. We have procedures for validating autoclave operation.

But a new paradigm has arisen in our test-happy world. In an effort to be more precise about level of cleanliness, industrial hygienists have developed a new system: Level 1, Level 2, etc.

Cleaning Equipment

Is medical equipment disinfected or sterilized? Both. Devices that enter the body are sterilized. Most items that touch only the skin are disinfected, unless the area of the body being treated is prone to sores (e.g. feet of diabetic patients.) So surgical and biopsy instruments are sterilized as are cytoscopes. Stethoscopes, oximeters, bedpans,, and EEG leads are disinfected.

Syringes and needles must be sterilized if they are to be reused, which is one reason the medical industry has moved toward one-time use products. One side effect of this has been an increase in sharps waste. Insufficiently cleaned injection hardware is very dangerous and results in over 20 million infections of hepatitis and HIV every year worldwide.

If syringes must be re-used, the CDC recommends they not be shared from one person to another. The CDC recommends syringes be washed with bleach between uses.

Mechanical devices include ultrasonic cleaners, washer-decontaminators, washer-disinfectors, and washer-sterilizers.

The FDA and EPA publish lists of disinfectants on critical devices and semi-critical devices to reduce the spread of microbial pathogen in medical facilities.

Glutaraldehyde is the most common type of chemical sterilant which is used in medical facilities such as a dialyzer, respiratory therapy equipment, endoscopes and hemodialysis etc.

Ethylene oxide (a gas) is used to disinfect equipment.

Washing Hands

Washing hands was one of the earliest measures taken to control disease transmission in clinics, even before the germ theory of infection was understood. It continues to be an important part of medical care today. A square centimeter of human skin on the forearm contains on the order of 10,000 colony-forming units of bacteria. Washing the hands does not eliminate all bacteria, but a good washing can eliminate more than 90 percent of bacteria and cut the risk of disease transmission.

Medical professionals have their own guidelines and recommendations on hand washing for certain situations. Rinse water, even a rinse of skin with patient blood on it, can be sent down the drain into the municipal sewage system. Bulk blood should be managed separately as biomedical waste.

Cleaning Glossary

class of organic compounds. When used in an industrial, medical, or hygiene context, the word is too vague. Specific compounds are named. When you see a chemical that has a name ending in “ol”, it is an alcohol. The type of alcohol in beverages is called ethanol or ethyl alcohol. A common rubbing alcohol is isopropyl alcohol (isopropanol). Many alcohols are used in cleaning preparations.
drug that fights microbial infection, or more broadly, a chemical, radiation source, or process that inhibits growth of microbes, especially pathogens. Includes antibiotics (which stop the growth of bacteria) and antifungals (which stop the growth of fungi).
a material that prevents or slows the growth of pathogens. Usually refers to a solid, liquid, or gel that is applied to a person’s body, or less frequently, an inanimate object. When a person is given an injection, the alcohol wipe applied to the skin is an antiseptic. Another b way to think of it: antimicrobials that are "indicated" for use on the body are antiseptics.
cleaned from pathogenic organisms. The word combines the prefix a-, meaning "not," and septic, meaning "putrifying".
also called para-chloro-meta-xylenol (PCMX). C8H9ClO - alcohol compound used as (1) an antiseptic, and (2) disinfectant for facilities and equipment. Commercial preparations of Chloroxylenol are usually in a solution with water, and often with isopropyl alcohol, surfactants, and oils.
disinfection or sterilization of infected articles to make them suitable for use
surfactant material that is not soap. “wetting agent and emulsifying-agent properties” Some detergents are water-soluble and some are soluble in organic liquid. All facilitate wetting and cleaning by having hydrophobic and hydrophilic sections. They permit formation of micelles and hence are “emulsifying agents”.
material or process that kills most pathogens, but not to the extent that a sterilant does.
Electrolyzed water
aqueous solution of hypochlorous acid (HOCl) and sodium hydroxide (NaOH). Used as a disinfectant. Made by electrolyzing a sodium chloride solution in water. Can be produced on-site so chemical does not have to be shipped into facility.
ethyl alcohol - one of the simplest alcohols, widely found in alcoholic beverages. Has antiseptic properties at high enough concentrations (wine is not concentrated enough), but rarely used in the clinic. Commercial preparations for disinfection are over 50 percent ethanol by volume with the rest water.
CH2O - can be used as disinfectant as it kills bacteria and fungi. Also acts as a preservative.
anything that kills germs. covers chemicals given to living bodies (antibiotics and antiseptics) and chemicals used on inanimate objects and buildings (sanitizers, disinfectants, and sterilizers.)
High Level Disinfectant
a germicide that inactivates all microbial pathogens, except large numbers of bacterial endospores. The FDA further defines a high level disinfectant as a sterilant used under the same contact conditions except for a shorter contact time.
isopropyl alcohol - C3H8O - common alcohol used in the home and in the clinic (rubbing alcohol)
Minimum Effective Concentration (MEC)
the lowest concentration of a liquid chemical germicide, which achieves the microbicidal activity the manufacturer/seller claims. The MEC is determined by dose response testing.
Peracetic acid
CH3CO3H - widely used as an antimicrobial for disinfecting surfaces
carbolic acid - C6H5OH - chemical with many uses, including as a feed for synthesis of more complex compounds. Sometimes employed as an antiseptic, although not as often as it was in the past.
Sodium hypochlorite
NaClO - also called "bleach" - Aqueous solution can be used as a germicide.
material or process that kills or deactivates bacteria, bacterial spores, fungi, and viruses. The implication is that the surface or object exposed to the sterilization process will not give rise to life, although in actual practice, sterilization usually means a high percentage of pathogens are destroyed.
Survivor Curve
death rate kinetics for a specific microbicidal agent on a defined microbial population
2-isopropyl-5-methylphenol, C10H14O - alcohol chemically similar to phenol. Used as an antiseptic. The name comes from the herb thyme, which the compound was first derived from.

Greener Cleaning

We generally want greener operations - less impact on the environment and threats to human health. Some businesses have developed products to meet this desire, and there are cleaning solutions advertised as safer than the older ones. However, don’t automatically assume these green cleaners are acceptable for your needs. If you are cleaning a healthcare or research facility - especially one with the possibility for infectious diseases, you need to give prime importance to disinfection efficacy.

How do you know if new cleaners are actually more green? Environment Canada has their Environmental Choice Program And other countries have similar schemes. The Global Ecolabelling Network seeks to be an association of "environmental performance recognition, certification and labelling organisations."

While some products are designed to be simple substitutes for the old, more toxic disinfectants and administered in the same way, progressive safety professionals and waste managers know that a systematic approach to rethinking cleaning is more likely to yield the best results.