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.

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.

The more recent 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.

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, 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.

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 most 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.