The use of ATP meters is certainly gaining popularity and don't get me wrong, I think there is a place for their use, but in designing studies to help further the science behind cleaning and disinfection we MUST understand the limitations of some of the methods we are using. In October of last year, we posted a blog on ATP (ATP – a microbiologist’s square peg) the impetus of which was based on the realization that Environmental Service Managers and Infection Preventionists believed that ATP can be used to compare cleaning and disinfection efficacy between different disinfectants.
Truth is ATP CANNOT be used to compare the cleaning and disinfection efficacy between different disinfectant chemistries. If you talk to suppliers of ATP meters - they agree. This is not the intended use and such use could lead you down a slippery slope of unintended consequences. Since October of last year our research team has worked with several of the leading companies who supply ATP meters and at the CHICA-Canada conference held at the beginning of this month presented our findings with a research poster "Evaluating market leading ATP meters for the reliability of their test results as measurement tools for surface cleanness in Healthcare applications". The following summarizes the findings:
ATP can be used as an indicator to determine cleanliness of a surface, however there are a number of limitations with its use:
1. The measurement of ATP is not standardized:
1. Each ATP meter has different detection limits therefore a statistical analysis must be done to ensure that consistent results can be achieved.
2. No ATP meter is the same.
3. Each ATP meter has its own minimum detection limit – if the contamination of a surface is below a certain level the ATP meter may not be able to detect it. This means that a surface can have significant contamination and have an ATP reading of zero!
2. Chemical interference from residual cleaners and disinfectants has an effect on the ATP readings:
1. Disinfectant and cleaning chemistries can either quench – causing false low readings as seen with bleach or enhance – causing false high readings as seen with quats and anionic surfactants (detergents).
2. There are two possible explanations for quenching:
a. The disinfectant ingredients are breaking the ATP molecules and thus they are no longer active/detectible;
b. The disinfectant ingredients enter into the enzymatic reaction from the swab and interfere with the enzymatic pathways for luminescence production.
3. The level of quenching (providing false low readings) with sodium hypochlorite (bleach) increases as the concentration of bleach increases.
4. These chemical interferences can give misleading results that can have significant implications on interpretation of data.
3. There is conflicting evidence to support a correlation between RLUs and the bacteria left on a surface (the amount of bacteria is determined by Colony Forming Units or CFUs):
1. Some studies show a correlation between RLUs and CFUs, other studies show a loose correlation while other studies have not examined the correlation between the two.
I completely stand behind the fact that ATP can be used to assess the effectiveness of a cleaning program but if used for quality control measures the results should be cautiously interpreted and at least periodically checked with plate counting methods. As illustrated in our study, depending on the sensitivity of the ATP meter, even high levels of contamination on the surface may not be detected. This can lead to a false confidence in the cleaning program. Most importantly, ATP CANNOT AND SHOULD NOT be used to compare cleaning or disinfection effectiveness between difference chemistries. Different chemistries have distinctive quenching or enhancing effects on ATP readings making meaningful and accurate evaluations between cleaning/disinfectant chemistries unreliable as the RLU readings do not account for such differences.
If you're looking to change cleaning and disinfecting products and are looking at the use of ATP to determine which product works better I hope you'll think twice!