Monday, 6 July 2020

Rogue Biological Indicators: Are They A Real Phenomenon?


Sometimes, unexplained results occur when using biological indicators with sterilization or decontamination processes. This could be attributable to a failure of the sterilization process or, perhaps, due to a mishandling of the biological indicator. Other reasons can be traced to issues of resistance and variations with the biological indicator itself (the effect of ‘creeping resistance’ has been described by some microbiologists to indicate a steady rising of D-values). Atypical results are seemingly more common with hydrogen peroxide vapor cycles (commonly used for isolator bio-decontamination) compared with sterilization cycles based on moist heat. In relation to hydrogen peroxide, another reason for atypical results is due to the occurrence of a rogue biological indicator, and it with this that this paper focuses on.

Tim Sandle has written a new article.

Here is an extract:

A rogue biological indicator is a term applied to a biological indicator which survives a hydrogen peroxide vapor cycle when perhaps it should not, based on the cycle parameters meeting previously established satisfactory profiles and in relation the known characteristics of the organism (that is, all cells should theoretically have been killed). When a positive biological indicator occurs (as evidenced by turbidity in culture media) it is impossible to determine whether the biological indicator met the definition of a ‘rogue’ (where a rogue can occur due to the overlaying of bacterial endospores on the carrier, as well as other reasons, as discussed in the main body of this paper).

As a note of caution, there are various reasons for isolator cycle failures outside of the rogue biological indicator situation and the automatic assumption should be that the reason for a cycle failure is due to a rogue event. As the rogue event assumes a ‘false positive’, the logical steps is to attempt to disprove the ‘false positive’ and to identify an alternative reason for the failure (that is the assumption that the failure is genuine). If no other reason can be attributed then, and only then, should the possibility of the rogue biological indicator be assumed. These issues are explored below.


The reference is:

Sandle, T. (2020) Rogue Biological Indicators: Are They A Real Phenomenon?, Journal of Validation Technology, 26 (1):

For details, please contact Tim Sandle

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)

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