P3-52 Accuracy and Precision of Coliforms Testing in National Shellfish Sanitation Program

Tuesday, July 28, 2015
Hall B (Oregon Convention Center)
Ravinder M. Reddy , U.S. Food and Drug Administration , Bedford Park , IL
Robert Newkirk , U.S. Food and Drug Administration , Bedford Park , IL
Samantha Lindemann , U.S. Food and Drug Administration , Bedford Park , IL
Hossein Daryaei , Illinois Institute of Technology/IFSH , Bedford Park , IL
Matthew Kmet , Illinois Institute of Technology/IFSH , Bedford Park , IL
Steffen Uhlig , Quo Data , Dresden , Germany
Thomas Graham , U.S. Food and Drug Administration , Bedford Park , IL
Introduction: Laboratories and analysts participating in the National Shellfish Sanitation Program (NSSP) are certified by inspection as well as successful proficiency test (PT) participation. FDA PTs are analyst based and permit laboratories to use preferred methods to test shellfish samples. 

Purpose: Quantitatively analyze variability of analysts, laboratories and methods enumerating coliforms in shellfish waters based on 2013 and 2014 FDA PTs. 

Methods: Eight growing area and eight process water simulated shellfish samples were inoculated with coliforms at 10-80 CFU/100 ml.  The inoculation procedures, mixing methods and homogeneity/stability were verified according to ISO 17043 and 13528.  Participants utilized NSSP-approved methods (most probable number (MPN) or membrane filtration). A total of 119 analysts (48 laboratories) in 2014 and 121 analysts (48 laboratories) in 2013 tested simulated shellfish samples for total and/or fecal coliforms.

Results: Accuracy and precision were calculated according to ISO 13528. Analyst z-scores were based on robust consensus means. Fecal coliform reproducibility SD was 0.279 and 0.177 in 2013/14 for MPN, and 0.263 and 0.165 in 2013/14 for membrane filtration. Similar patterns were seen in process water samples where total coliform reproducibility SD was 0.305 and 0.197 in 2013/14 for MPN, and 0.275 and 0.158 for membrane filtration. Test on equivalency according the Q-Hampel method showed MPN and membrane filtration did not have equivalent performance across 8 growing and 8 process water samples in 2013. Means for MPN and membrane filtration were not equal, but the mean deviation fell within tolerated limits across 8 growing water and 8 process water samples in 2014.

Significance: Analysis of data from two consecutive annual PTs demonstrates method variability plays a role in coliforms testing and could affect enforcement of shellfish regulations. This study shows how large-scale PTs in relevant matrices can be used to generate method performance data and evaluate overall performance of laboratories.