Hard Surface Carrier Test for Efficacy Testing of Disinfectants: Collaborative Study

Abstract

Abstract A collaborative study was undertaken to evaluate a new disinfectant efficacy method called the hard surface carrier test. This new method is a qualitative carrier test that uses disposable glass carriers and standardized bacterial cultures. Ten laboratories tested 6 disinfectant-type formulations, which included positive and negative controls, against 3 microorganisms. No significant differences were found among the 10 laboratories for tests with Pseudomonas aeruginosa and Salmonella choleraesuis, but a small but statistically significant difference was present among laboratories for Staphylococcus aureus. The majority of data for this organism showed very good agreement; however, several tests exhibited slightly higher positive responses, which resulted in this overall difference. This difference was not considered significant within the scope and precision of this method or when compared with results for the other 2 organisms. The initial estimates of pure intralaboratory variance, determined from mean squares from analysis of variance results, were 1.009,0.295, and 1.553 for P. aeruginosa, S. aureus, and S. choleraesuis, respectively. The experimental error for S. aureus was 3-5 times smaller than for the other 2 organisms, which helps explain the statistical significance of the results observed with this organism. Final estimates of intralaboratory variance obtained after dropping nonsignificant terms from the models were 0.90,0.30, and 0.58 for P. aeruginosa, S. aureus, and S. choleraesuis, respectively. Small but statistically significant differences were noted in the formulation means for P. aeruginosa and S. aureus but not for S. choleraesuis. The results of this study suggested a performance standard of ≤2 positive carriers out of 60 tested for S. aureus and S. choleraesuis, and ≤3 positive carriers out of 60 tested for P. aeruginosa. This standard was derived from an analysis of the data by calculating an expected count of positive carriers and a 95% upper confidence limit for a set of 60 carriers. The method has been adopted first action by AOAC International.