Purpose: The purpose of this study was to evaluate the impact of culture-independent diagnostic testing in clinical and reference laboratories on public health laboratory surveillance.
Methods: One year of data submitted to the Tennessee Public Health Enteric Bacteriology Laboratory, comprised of 2,443 submissions of Salmonella, Shigella, Shiga Toxin-producing E. coli (STEC) and Campylobacter, was evaluated for submission type (isolate or specimen), organism requested, recovery rate and workload (picks or workups). Specifically, workload was evaluated by counting the number of isolates picked and worked up biochemically or with a molecular method to identify the organism.
Results: Culture-independent diagnostic testing comprised 25 - 45% of all Salmonella, Shigella, Shiga Toxin-producing E. coli and Campylobacter testing in all but the first month of the study. When comparing syndrome panels to EIA’s, syndrome panel testing comprised over 80% of the initial clinical testing in the later nine of the twelve months. Recovery rates from CIDT submissions were 63% for Salmonella, 73% for Shigella, 54% for STEC and 40% for Campylobacter. There is a diminishing return on investment for continued workups, with a different level of effort required depending on the organism and recovery rate sought after.
Significance: These data suggest the wide variety of recovery rates and workups required to identify Salmonella, Shigella, Shiga Toxin-producing E. coli and Campylobacter from a CIDT specimen indicating a need for public health laboratory recommendations. This guidance will be valuable until public health can implement an isolate-free surveillance system for foodborne illness pathogens.