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Friday, October 5, 2012

ATP – a microbiologist’s square peg

I admit it that there are times I can come across as being too zealous, but when I truly believe an injustice is occurring, then I need to do everything in my powers to ensure the issue is addressed.  The widespread misuse of ATP
(Adenosine Triphosphate) as a means for comparing the effectiveness of different disinfectants is something that I cannot leave unaddressed.  To me it’s the equivalent of trying to force a square peg into a round hole or for that matter trying to use margarine to make shortbread....when butter is the only way to go!

Don’t get me wrong, safe and effective disinfection of high-touch environmental surfaces is an important tool in reducing the spread of HAIs and the need for rapid and reliable means of monitoring the effectiveness of such practices are also crucial for training and quality control.  I do agree that ATP has its use; however, there are several limitations to the use of ATP within healthcare facilities.  First, the absence of standardization of the ATP technology from various manufacturers and RLU readings for use within healthcare makes cross-comparisons of readings and benchmarking problematic.  Second, the lack of documented correlation between ATP readings and levels of microbial contamination on environmental surfaces makes meaningful interpretation of the data difficult and distinction between pathogenic and non-pathogenic microbes on the sampled surface virtually impossible. Also, ATP kits cannot detect or measure viral contamination because viruses possess no ATP.  Third, and quite importantly, certain common surface disinfectant chemistries and cleaning tools may interfere to varying degrees with ATP measurements.   Therefore, the use of ATP as a tool to determine the effectiveness of different cleaning practices or to compare the effectiveness of different cleaning and disinfectant chemistries remains a challenge. 

While we have written a Technical Bulletin addressing each of the limitations, it’s the limitation in the use of ATP as a comparator tool that catches in my “caw” so to speak.    From an infection control perspective, we want to ensure that we choose the best disinfectant for our programs so the ability to create numbers to compare different disinfectants is of great interest.  Unfortunately, in our attempts to generate numbers, we have overlooked the limitations of the ATP test itself. 

The issue of different cleaning chemistries and their potential to enhance or quench ATP bioluminescence is especially significant.  Quats and anionic surfactants, for example, may give false positive results by enhancing RLU readings by as much as 10%.  One study with Hydrogen Peroxide showed that concentrations of 0.1% did not have any enhancing or quenching effects on the RLU levels; at 0.5%, quenching effects of 3 - 5% were observed. On the other hand, chlorine has been shown to have both enhancing and quenching effects.  At concentrations of 100 ppm chlorine has been shown to significantly enhanced RLU readings.    As concentrations increased to 500 ppm neither quenching or enhancing effects were observed, but as levels of chlorine increase to those (e.g., 1,000-5,000 ppm),  routinely used for environmental surface disinfection in healthcare facilities there may be as much as a 40% deviation in quenching, thereby potentially giving false negatives!  Consequently, Boyce et al in their study on the use of ATP for monitoring the effectiveness of hospital cleaning excluded all those rooms which were disinfected with a 5,000 ppm bleach solution.

I’m not saying it’s wrong to use or that we should not use ATP measurement kits to assess the degree of cleanliness of cleaned and disinfected surfaces in healthcare settings.  I am simply asking that caution is used in the interpretation of the results because several published studies have now documented the potential of cleaning tools and disinfectant chemistries to either enhance or suppress the levels of RLU and may in fact lead to either an over-estimation or an under-estimation of the surface decontamination procedures in place.

Just as making a good shortbread requires butter, if you want to really know how well a disinfectant is working (e.g. killing the bugs) you need to conduct microbiological testing. 

Bugging Off!




1 comment:

  1. Hi,

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