The EPA's "Test Method for Residual Self-Sanitizing Activity of Copper Alloy Surfaces" is designed to quantitatively test the ability of copper alloy surfaces to kill 99.9% of the target microorganism for 24 hours, after multiple simulated wear cycles and re-inoculations. In order to obtain a residual self-sanitizer claim, an initial copper sufrace sanitizer evaluation must be performed. 

Summary of the EPA Method for Residual Self-Sanitizing Activity of Copper Surfaces
  • The test surface must pass the EPA's "Test Method for Efficacy of Copper Alloy Surfaces as a Sanitizer" prior to testing for residual self-sanitizing activity. 
  • The test culture is prepared from stock cultures by incubation in appropriate broth.
  • The suspension of test microorgnaisms is then standardized by diltuion in broth.
  • Organic soil is added to the inoculum to simulate "dirty" conditions.
  • An initial sanitizer evaluation is performed by inoculating test and control carriers, in quadruplicate, allowing them to dry fully prior to the start of the 2 hour contact time. These carriers are then eluted, diluted and plated to determine concentrations of viable microorganisms on the surfaces.
  • Separate control and test carriers are subjected to a standardized wet/dry abrasion procedure to simulate wear. These carriers are re-inoculated with a lower concentration of micoorganisms between wear cycles.
  • These "worn" carriers are then subjected to a final sanitizer test, wherein test and control surfaces are reinoculated, allowed to dry for 30-40 minutes then exposed for the specified contact time, usually 2 hours.
  • Following the contact time, control and test surfaces are neutralized, diluted and plated to determine concentrations of viable microorganisms on the test surfaces.
  • For the test sample to be defined as a residual self-sanitizer, the test material must demonstrate at least a 3 log (99.9%) reduction within the specified contact time.
  • If antibiotic-resistant microoganisms are tested, such as Methicillin Resistant Staphylcoccus aureus (MRSA), antimicrobial susceptibility testing is required at the time of the study.

Strengths of the EPA Method for Residual Self-Sanitizing Activity of Copper Surfaces
  • The method is quantitative allowing for clear pass/fail indication and comparison with other studies of the same type.
  • The method is somewhat representative of actual surface contamination events since it takes into consideration the drying, wear and reinoculation of the test microorganisms as typically seen on environmental surfaces.

Weaknesses of the Method for Residual Self-Sanitizing Activity of Copper Surfaces
  • The repeat abrasion portion of the test may introduce variability from sample to sample.
  • Test sample composition, as stated in the title of the method, is specific to copper and copper alloy technolgoies. Sponsors should avoid using this method to test alternative technologies unless strictly for R&D purposes.
  • The method, as written, is fairly restrictive with regard to sample type. Test surfaces must not be waxed, painted, lacquered, varnished, or otherwise coated.
  • Label claims supported by this method are limited to indoor, hard, non-porous surfaces where cleaning practices are consistent.

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