How does susceptibility prevalence impact on the performance of disk diffusion susceptibility testing?

Area of Science:

• Clinical microbiology
• Antimicrobial resistance
• Diagnostic test evaluation

Background:

• Antimicrobial disk diffusion susceptibility testing is crucial for predicting antibiotic efficacy in clinical settings.
• Evaluating this method requires understanding predictive values, which are influenced by the prevalence of susceptible, intermediate, and resistant bacterial isolates.
• The impact of susceptibility prevalence on test performance needs rigorous quantification.

Purpose of the Study:

• To quantify the influence of susceptibility prevalence variation on the performance of the disk diffusion method.
• To analyze how changes in the frequency of susceptible, intermediate, and resistant isolates affect predictive values.
• To inform policies regarding zone diameter breakpoint determination and performance evaluation.

Main Methods:

• A modeling approach was employed to simulate the disk diffusion method.
• Simulations utilized a resampling procedure from two distinct minimum inhibitory concentration/diameter datasets.
• Experimental variability in minimum inhibitory concentration and diameters was incorporated into the simulations.

Main Results:

• The impact of susceptibility prevalence on disk diffusion performance is antibiotic-dependent.
• Significant performance variations were observed when prevalence changes were substantial.
• The study highlights the critical role of prevalence in interpreting test results.

Conclusions:

• Susceptibility prevalence must be more rigorously considered in breakpoint determination and performance evaluation studies.
• Disk diffusion breakpoint consistency requires re-evaluation when prevalence variation is significant.
• Estimating the consequences of international breakpoint consensus on prediction quality and patient management is essential.