Wednesday, September 16, 2009
04:30 PM in REC 315
Professor Bruce Craig
Department of Statistics, Purdue University

The calibration of two susceptibility tests based on interval censored data with measurement error

Abstract

Drug dilution (MIC) and disk diffusion (DIA) are the two common tests used by clinicians to determine pathogen susceptibility to antibiotics. For each of these tests, two drug-specific breakpoints classify the unknown pathogen as either susceptible, intermediate, or resistant to the drug. While MIC breakpoints are largely based on the pharmacokenetics and pharmacodynamics of the drug, comparable DIA breakpoints are not as straightforward to calculate. Current Clinical and Laboratory Standards Institute (CLSI) guidelines require a scattergram of test results for numerous pathogens and the DIA breakpoints are based on limiting the classification discrepancies. This approach, however, is limited by the fact that certain experimental errors are ignored. I will discuss this error-in-variables problem and then describe a hierarchical model, which factors in the uncertainty of both tests, the drug-specific relationship between the two tests, as well as the underlying distribution of pathogens. For the drug-specific relationship between these two tests, I propose both a parametric and nonparametric model. A loss function is then used to determine the DIA breakpoints.

This is joint work with the CLSI Subcommittee on Antimicrobial Susceptibility Testing.