SURFACE CARRIER TEST AS A QUANTITATIVE TEST OF DISINFECTION - A COLLABORATIVE STUDY

The hard surface carrier test (HSCT) recently was proposed as a qualit ative test for disinfectant efficacy, A collaborative study of HSCT le d to a suggested performance standard of less than or equal to 2 or 3 positive carriers out of 60 tested, Subsequently, it was discovered th at HSCT can be used as a quantitative test, because the HSCT protocol requires measurement of inoculum level on some carriers, The data allo w estimation of the log(10) reduction in number of active bacteria, Pr oducers, consumers, and policy-makers will be better able to discuss m erits of alternative performance standards if the focus is on log redu ction of organisms rather than on number of positive carriers, Data fr om the collaborative study were reanalyzed from this quantitative view point, If the point estimate of log reduction is LR and the 99% lower confidence limit estimate is LLR, the LR values ranged from 7.0 to 9.0 and the LLR values were greater than 6.0 for all disinfectants except the negative control formulation, The total variance for estimated LR is the sum of interlaboratory and intralaboratory variances, The tota l variance for LR was 0.095 for Pseudomonas aeruginosa, 0.251 for Stap hylococcus aureus, and 0.118 for Salmonella choleraesuis, Percentages of the variance due to interlaboratory variability were 11% for P. aer uginosa, 52% for S. aureus, and 25% for S. choleraesuis, Chances of ma king false-effective and false-ineffective decisions can be calculated for the quantitative HSCT The performance standard can be based on LL R.