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Is it a 6.0-log or a 6-log reduction?

Acceptance criteria for disinfection validations that are outlined in AAMI TIR12:2020[1] specify that depending on the disinfection level either a 3-log or a 6-log reduction of appropriate microorganisms should be achieved. Mathematically one might be inclined to consider a 5.8-log reduction is the same as a 6-log reduction, which prompts the question as to how to handle the rounding of results when interpreting data from disinfection validations. Whereas no specific guidance is provided in any guidelines or standards concerning this issue, it is our experience that neither certain European notified bodies nor FDA will find the rounding of results acceptable. That means that a 5.8-log reduction, for example, cannot be considered a 6-log reduction.

Consequently, if a 3.0- or 6.0-log reduction is not achieved when performing disinfection validations the only possible course of action is to amend the procedure to achieve the 3.0- or 6.0-log reduction required, even if the achieved disinfection level is very close to these values. One possible exception could be devices that fall in the category of non-critical, non-patient contacting devices that pose a low cross-contamination risk to patient care. While it is understood that these devices should be disinfected given the contribution of cross-contamination to hospital acquired infections, meeting a 6.0-log reduction (as required for low-level disinfection as outlined in AAMI TIR12:2020) may not be achievable without putting a considerable burden on healthcare practices. In these cases, it may be worthwhile to take a risk-based approach to determine if the disinfection level achieved is justifiable rather than re-doing the validation.

[1] AAMI TIR12:2020 “Designing, testing, and labeling medical devices intended for processing by health care facilities: A guide for device manufacturers”

Alpa Patel

Alpa Patel

B.S., RM (NRCM)
Principal Scientist

Alpa Patel is a certified microbiologist and has been part of the medical device industry for 18 years specializing in cleaning/disinfection and sterilization of reusable medical devices, endoscopes and validation of tissue disinfection or sterilization processes. Her current role as a principal scientist at Nelson, involves overseeing test method validations for reprocessing, writing standard test...

Lise Vanderkelen

Lise Vanderkelen

PhD
Pharmaceuticals and Microbiology Expert

Lise Vanderkelen received her Ph.D. from the Faculty of Bioscience Engineering at the University of Leuven (Belgium) in 2012. She started at Nelson Labs Europe in 2013 as Study Director Extractables & Leachables, focusing on parenteral applications, and in 2014, she became responsible for the chemical characterization testing of medical devices (ISO 10993-18). In 2016,...