ABSTRACT
OBJECTIVES: The aim of this study was to evaluate the accuracy of various susceptibility methods when testing cefuroxime against a collection of Escherichia coli isolates with MIC values close to the breakpoint. METHODS: 80 E. coli strains with a cefuroxime MIC value of 16 mg/L obtained by broth microdilution with Vitek 2 were selected. Microdilution was considered the reference standard and was performed in duplicate, as were disc and gradient diffusion tests using two different manufacturers in each case. EUCAST 8.0 breakpoints were used for MIC interpretation. RESULTS: All strains were resistant according to Vitek 2 (MIC 16 mg/L) but 72.5% (58/80) were classified as susceptible by reference standard microdilution. Categorical and essential agreements between Vitek 2 and reference standard microdilution were 27.5% (95% CI 1.9-1.4) and 86.3% (95% CI 0.8-0.9), respectively. Differences are statistically significant when isolates are classified as 'susceptible' or 'resistant' according to EUCAST breakpoints between diffusion methods (disc and gradient) and reference standard microdilution. Using BioMérieux (BM) and Liofilchem (LF) gradient testing, 24.1% (14/58) and 13.8% (8/58) of results were identified as false susceptible and 4.5% (1/22) and 40.9% (9/22) were found to be false resistant, respectively. Using Oxoid (OX) and Bio Rad (BR) cefuroxime discs, 22.5% (13/58) and 17.2% (10/58) of results were false susceptible and 9.1% (2/22) and 13.6% (3/22) were false resistant, respectively. DISCUSSION: Intertechnique variation around the cefuroxime breakpoint was a considerable source of disagreements and seriously affected the clinical classification of the isolates. We propose that the definition of the area of technical uncertainty (ATU) be modified to include the variability between approved AST methods.
Subject(s)
Anti-Bacterial Agents/pharmacology , Cefuroxime/pharmacology , Microbial Sensitivity Tests/methods , Microbial Sensitivity Tests/standards , Escherichia coli/drug effects , Escherichia coli/isolation & purification , Humans , Reference Standards , UncertaintyABSTRACT
OBJECTIVE: To compare normal users (NU) and over-users (OU), examining social and demographic features, family characteristics, presence of psychological problems or family dysfunction and the existence of chronic pathologies. DESIGN: An observational crossover study, lasting one year (1994). SETTING: Health centre. PATIENTS AND OTHER PARTICIPANTS: Randomised sampling of 12,092 patients > 14 years old. OU (n = 260) was defined as someone who had a percentage point for attendance without an appointment at the Centre, excluding bureaucratic reasons, of above 75%; and NU (n = 260), in the 25 and 75% band. 65 individuals (240 OU and 225 NU) took part. MEASUREMENTS AND MAIN RESULTS: Average age of OU was higher than that of NU. 88 OU (36.7%) finished their education above primary level, whereas 115 NU (51.1%) did so (OR 1.81). 37.5% OU (90) belonged to small families, against 24.9% NU (56). 34.6% OU (83) were in an advanced family vital cycle, against 24% NU (54. 26.7% OU (64) and 17.8% NU (40) had psychological problems. There was family dysfunction in 32 OU (13.3%) and 23% NU (10.2%). 186 OU (77.5%) had some chronic pathology, against 96 NU, of whom 70.3% OU and 87.2% NU attended appointments arranged to monitor these pathologies. CONCLUSIONS: Over-use of our health centre is related to being older, a low level of education, belonging to small families in an advanced vital cycle, having psychological problems, suffering chronic pathologies and not attending appointments when they are arranged.
