Pulsed‑UV : Decontamination ? Disinfection ? or Sterilization ?

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Sterilization, what’s that? 

This is a complete destruction of all forms of life. The European standard EN556 about the sterilization of medical devices, specifies that a probability of a viable microorganism on a device of 10-6 hast to be achieved in order to designate a medical device as sterile.  

It exists also the term SAL « Sterility assurance level » :

  • The degree with which several systems are made sterile
  • Probability that a system is not sterile
  • Acceptable level of non‑sterile system (1/1000000)

The SAL is a procedure to ensure a probability of not more than one viable microorganism in an amount of one million would have a chance of surviving the sterilization process. 

The SAL is, therefore, a probability that is … perfectly sure !

Sterilization with pulsed light used, generally, to prove their efficiency Aspergillus brasiliensis spores (mold) or Bacillus brasiliensis (bacteries). 

Aspergillus brasiliensis spores and Bacillus atrophaeus spores, as challenge organisms, are perfeclty adapted for UV light system due to their high UV‑resistance.

If Pulsed Light systems are able to kill 106  of these two micro‑organisms, all the other germs will be more easily destroy and the system will have more chance to be sterile (as requested by the NAS)!

 

Some rules about the sterilization levels

However, it’s important to note that the sterilization is possible only for items already DRY and CLEAN.

Consequently, do not waste time to ask for sterilization of dusty and dirty objects. It’s just will not work. Some cleaning step and dry are necessary before the sterilization procedure, even if the process is able to prove the 6 log reduction.

In this case, the term « sterilization » could not be used and the terms « decontamination » or « disinfection » were preferred. There is no « happy medium ». A surface is either STERILE or NOT !

 

Decontamination, disinfection sterilization : how to define them ?

Difficult to find a clear definition for each word.

Let’s take the definition of the dictionnary  (www.dictionary.com):

Decontamination

To make free of contamination ; purify

Disinfection

To cleanse of infection ; destroy disease germs in. 

Sterilization 

Destruction of all living micro‑organisms, as pathogenic or saprophytic bacteria, vegetative forms and spores. 

 

Finally, the definitions as presented above are all the same.

The following is suggested definitions for decontamination disinfection and sterilization and a proposal that considers the log reduction level associated. This table can be commented on and open up the debate.

Decontamination

Reduction of the number of micro‑organisms to make items or environment,  safe and harmless before disposal, according to the standard in force.

LOG 2

LOG 3

Disinfection

Process to inactivate all pathogenic micro‑organisms (except bacterial spores) without leading to the achievement of level zero. The aim is to eliminate the risk associated with the presence of certain germs. The infection risk is eliminated.

LOG 4

LOG 5

Sterilization

The complete and sustainable destruction of all forms of life, as the probability of a microorganisms surviving sterilization being one in one million.  

LOG 6

 

Could pulsed‑UV sterilize ?

Yes pulsed light could sterilize. How ?

  • First of all, pulsed light prevents DNA replication due to the high peak power pulses, the broad spectrum and particularly, the important UV dose. The microorganisms are sustainably inactivate.
  •  Secondly, it kills DNA and inactivates all type of microorganisms (including spores, molds, virus, etc.). That is why we can consider pulsed light technology as a possible sterilization system.

And YES, if the technology is correctly used. Do not forget that an item could be sterilized only if it is clean and dry. This must be ensured and if not, the solution would be to combine the pulsed light technology with a cleaning step and a drying step. Moreover, the light must have a sufficient and controlled intensity  to achieve a 6‑LOG reduction level.

References :

https://ehs.colorado.edu/resources/disinfectants-and-sterilization-methods/

https://www.sciencedirect.com/topics/chemistry/sterilization-and-disinfection

https://www.dictionnary.com