Ineffectiveness of hospital disinfectants against bacteria: a collaborative study

A collaborative study was undertaken to assess the degree of variability in disinfectant efficacy test results among laboratories that routinely perform the Association of Official Analytical Chemists (AOAC) Use-Dilution Method. Eighteen laboratories tested identical samples of six EPA-registered, hospital-grade disinfectants (three phenolics and three quaternaries) at the manufacturers' recommended use-dilution using only those modifications of the method approved by the AOAC Use-Dilution Task Force. Each laboratory processed 60 penicylinders for each of the 6 randomly selected disinfectants and 3 test organisms. The current EPA pass criterion for a disinfectant requires a test result of less than or equal to 1 positive penicylinder/60 replicates tested When compared with the 1 positive/60 replicate criterion, the test results of the 6 disinfectants were: 86 trials (80%) passed and 22 trials (20%) failed against Salmonella choleraesuis ATCC 10708; 71 (66%) passed and 37 (34%) failed against Staphylococcus aureus ATCC 6538; and 41 (38%) passed while 67 (62%) failed against Pseudomonas aeruginosa ATCC 15442. Four laboratories unknowingly tested their own product, and three of the four failed their product against one or more of the test organisms. These results show the inability to reproduce the manufacturers' bactericidal label claims for 6 disinfectants against the 3 AOAC test bacteria. In addition, extreme variability of test results among laboratories testing identical products questions the use of the AOAC Use-Dilution Method for enforcement action.