Should the AOAC use-dilution method be continued for regulatory purposes?

Despite its very poor reproducibility, AOAC INTERNATIONAL's use-dilution method (UDM) for bactericidal activity (AOAC Methods 964.02, 955.14, and 955.15) has been required by the U.S. Environmental Protection Agency (EPA) since 1953 for regulatory purposes, while methods with better reproducibility have been adopted in Canada and Australia. This study reviews UDM from a statistical perspective. Additionally, the test's expected results were compared to those obtained from actual evaluation of several formulations. Significant gaps have been identified in the reproducibility of the test data as predicted by statistical analysis and those presented to the EPA for product registration. UDM's poor reproducibility, along with its qualitative nature, requires the concentration of the active ingredient to be high enough to ensure all or most carriers to be free of any viable organisms. This is not in accord with the current trends towards sustainability, human safety, and environmental protection. It is recommended that the use of the method for regulatory purposes be phased out as soon as possible, and methods with better design and reproducibility be adopted instead.