Purpose: This study analyzes data collected from fifteen PT studies completed in the United States and Canada over the course of eight years. These studies were conducted in various food matrices and represent results obtained from city, state, federal, public health, and private laboratories.
Methods: Food and veterinary diagnostic samples were artificially inoculated with Salmonella serovars and confounding cultures ranging from 1-105 CFU/g to mimic actual samples. Participants were instructed to isolate, identify, and confirm Salmonella serovars utilizing routinely used methods. Food matrices studied included black pepper, lettuce, liquid eggs, infant formula, catfish, and veterinary diagnostic samples.
Results: Among 916 total participants, the passing rate was over 92% across fifteen Salmonella PT studies. Out of 72 analysts testing black pepper, 88% detected atypical Salmonella Heidelberg, while 100% of analysts were able to detect typical Salmonella serovars. In veterinary samples analyzed by 25 participants, 83% correctly detected Salmonella Typhimurium at 1 CFU/g and 76% correctly detected Salmonella Heidelberg at 1 CFU/g. Detection of Salmonella Typhimurium in bagged lettuce among 75 participants was 99% and 100% when inoculated at 10-20 CFU/g and 99% correct when inoculated at 110-180 CFU/g. The overall passing rate of Salmonella detection was 100% in bagged lettuce, black pepper, and liquid eggs; while average passing rate in veterinary diagnostic samples was 92% and 100%.
Significance: The studies summarized indicate analyst proficiency is robust in the detection of typical and atypical Salmonella serovars. Preparation of samples according to principals of ISO 22117 with inoculation levels near the limit of detection and confounding organisms could be used to identify the problematic areas of Salmonella detection in food.