What Is Categorical Agreement

Fifty staphylococcus isolates and 50 enterococci isolates were tested for linezolid sensitivity by broth micro-dilution, disc diffusion, Etest, MicroScan, Phoenix, VITEK and VITEK 2. The categorical and essential agreements on the results of the six micro-dilution methods are presented in Table 1.1. The results for each method are listed below. Isolates for which very significant or major errors have been reported are shown in Table 22. All systems were tested in parallel with the inocula made from the same subculture. All isolates for which there were differences between the results of the test method (i.e. sensitive, moderate or resistant) and the results of the reference method for micro-dilution broth were again tested in parallel by the micro-dilution of the broth and the method in question; However, only the initial results were used in error calculations. If two or more systems did not agree with the broth reference result, all systems were retested in parallel to determine the reproducibility of the results. In a categorical agreement, very large errors were defined as being sensitive to the outcome of the test method and the results of the reference method being resistant, larger errors were identified than those for which the result of the test method was resistant and where the result of the reference method was fragile, and minor errors are defined as those for which one of the two methods reported a result in as an intermediate product and the other reported the result as vulnerable or resistant.

Very high error rates were calculated using the 15 non-receptive isolates as denominators for staphylococci and the 15 resistant isolates as denominators for enterococci. For larger error rate calculations, the denominators were 35 for staphylococcus and 33 for enterococci. For smaller error rate calculations, the total number of organisms tested was used as a denominator, including two E. faecium isolates that were in the meantime too linear. Essential compliance was calculated for MIC methods by determining the number of test results within ±1 of doubling the dilution of the MIC obtained by the reference method. The Phoenix system entered into an 89.6% category agreement with the reference method for micro-dilution of broth, although the overall essential agreement was higher (95.8%). The trials were interrupted by the system twice before the completion of three organisms (an isolate of S. epidermidis, S. aureus and E. faecium), all sensitive to linezolide by the broth reference method, so that no results were available for these organisms.

An isolate s. hominis (also sensitive to linezolid) was not able to develop in the phoenix test field during the first tests, but increased in subsequent tests. The Phoenix system reported that four non-linear-sensitive staph isolates, of which three s. aureus isolates (5721, 3036 and 3487) and one epidermidis isolate (0538) were susceptible, resulting in a very high error rate of 26.7% for staphylococcus (Tables 11 and 2).