The medical world employs strict rules about when equipment is clean enough for internal or external use. There is a difference whether something is used on intact skin, broken skin, mucous membranes, or during surgery in the body. In fact, intact skin provides the best protection against micro-organisms. A wound or an open surgical area offers much less protection. There are therefore different requirements for how clean material must be in order to be used in a particular situation.
There are various organisations worldwide that set these rules, but in general the rules are fairly similar. For example, the RIVM follows the European standard EN 13060 for sterilization, while the Centers for Disease Control and Prevention (CDC) in the United States follows the rules of the FDA. In order for a disinfection method to be used worldwide, it must comply with all these rules.
In order of thoroughness, the RIVM defines the following definitions for cleaning medical equipment:
- Cleaning: The removal of visible or adhered dirt and invisible organic material to prevent micro-organisms from maintaining, multiplying and spreading.
This can be done dry: for example by dusting, vacuuming, sweeping or wiping.
Or wet: with water and a cleaning agent, for example.
- Disinfection: The thermal or chemical killing or inactivation of micro-organisms. This reduces the number of micro-organisms to an acceptable level.
Thermal disinfection: an example is pasteurization, which is often applied in the food industry (milk, beer, wine).
Chemical disinfection: this can be done with chlorine preparations based on sodium dichloroisocyanurate, with higher concentration (70-90%) alcohol solutions or with water peroxide.
A third way is irradiation with UV technology: this is not new, but it is emerging because of the speed and environmental aspects.
- Sterilisation: A process that kills or inactivates all micro-organisms on or in an object. This reduces the chance of living organisms being present per sterilised unit to less than 1 in 106.
Sterilisation is a process that requires more expertise. Specially trained persons often carry it out. Frequently used methods are heat sterilisation, radiation sterilisation, ethylene oxide sterilisation and steam sterilisation in combination with formaldehyde.
The thoroughness of the cleaning is thus related to the application, and thus also to the risk of infection. This is why medical equipment that comes into contact with the skin and mucous membranes is disinfected. And medical equipment that is intended for use in the body (a pacemaker) or, for example, in blood vessels (a needle or a stent), is sterilized before use.
"For example, you obviously can't disinfect milk, beer, or wine with chlorine or high concentrations of alcohol because that makes it undrinkable."
Difference between cleaning, disinfecting and sterilising
The difference between cleaning, disinfecting and sterilizing is not only in the method used to achieve the desired result. There is a further difference in which type of micro-organisms are inactivated or killed. Sterilising also renders bacterial spores (a small survival form of some bacteria) harmless. Disinfection methods are not as effective against these spores. See Fig 2.
Which method is best to use?
Which method can best be used for which purpose depends on the various advantages and disadvantages. For example, you obviously cannot disinfect milk, beer or wine with chlorine or high concentrations of alcohol because that would make it undrinkable. And the examination table at the doctor’s office is difficult to heat to 70 degrees Celsius for 20 minutes between two consecutive patients. Some materials cannot withstand the heat of steam or the pressure of an autoclave. Sometimes two methods are equally effective, but you prefer a cheaper or more environmentally friendly solution. Different uses therefore require different methods, all to reduce the risk of infection to an acceptable level. Technology based on UV can be used for disinfection of medical equipment that is used externally. With this level disinfection method, disinfection is fast and thorough and the device can be used immediately for the next patient.
Would you like to know more about reducing live micro-organisms? Then be sure to read this article too: What is log reduction and what is it used for?