Date of Award

12-18-2013

Degree Type

Thesis

Degree Name

Master of Public Health (MPH)

Department

Public Health

First Advisor

Dr. Lisa Casanova

Second Advisor

Dr. John Papp

Abstract

Background: Clinical breakpoints and epidemiological cut-off values for N. gonorrhoeae azithromycin antimicrobial susceptibility testing have not been established. This study utilized existing minimum inhibitory concentration (MIC) data from CDC’s Gonococcal Isolate Surveillance Project (GISP) to establish epidemiological cut-off values for azithromycin and N. gonorrhoeae as determined by agar dilution.

Methods: MIC distributions for the pooled dataset and each data year (2005-2012) were constructed. Epidemiological cut-off values were calculated using two methods. Method 1 considers the wild-type MIC distribution, the modal MIC for the distribution, and the inherent variability of the test (±1 twofold-dilution). Method 2 defines the epidemiological cut-off value as two twofold-dilutions higher than the MIC50.

Results: Taking into consideration the wild-type MIC distributions and the inherent variability of the test, the epidemiological cut-off value chosen for the pooled dataset and each data year using Method 1 was ≤1.0 µg/mL. The MIC50 for the pooled dataset and each data year was 0.25 µg/mL. Two twofold-dilutions higher than the MIC50 (0.25 µg/mL) for the pooled dataset and each data year was 1.0 µg/mL.

Discussion: The epidemiological cut-off values chosen using Methods 1 and 2 (≤1.0 µg/mL) were identical for the pooled dataset and each data year, indicating the epidemiological cut-off value has not changed from 2005-2012. The epidemiological cut-off value for N. gonorrhoeae azithromycin agar dilution antimicrobial susceptibility testing established during this study can be used to help set clinical breakpoints and identify isolates with reduced susceptibility to azithromycin.

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