Confounding Role of Salmonella Serotype Dublin Testing Results of Boneless and Ground Beef Purchased for the National School Lunch Program, October 2013 to July 2017

Scott L. Vial, Darin R. Doerscher, Carl M. Schroeder, Ali Strickland, Craig W. Hedberg

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


ABSTRACT: The Agricultural Marketing Service procures boneless and ground beef for federal nutrition assistance programs. It tests procured beef for concentrations of standard plate counts (SPCs), coliforms, and Escherichia coli and for the presence of Salmonella and Shiga toxin-producing E. coli. Any lot exceeding predefined critical limits (100,000 CFU g-1 for SPCs, 1,000 CFU g-1 for coliforms, and 500 CFU g-1 for E. coli) or positive for Salmonella or Shiga toxin-producing E. coli is rejected for purchase. Between 1 October 2013 and 31 July 2017, 166,796 boneless beef lots (each approximately 900 kg) and 25,051 ground beef sublots (each approximately 4,500 kg) were produced. Salmonella was detected in 1,955 (1.17%) boneless beef lots and 219 (0.87%) ground beef sublots. Salmonella sample size increased from an individual 25-g sample to a co-enriched 325-g sample on 1 March 2015. Salmonella presence was associated with season (lowest in spring), larger sample size, and increased log SPC in boneless and ground beef. Increased log E. coli was associated with Salmonella presence in boneless beef, but not ground beef. Salmonella Dublin was the most common serotype in boneless beef (743 of 1,407, 52.8%) and ground beef (35 of 171, 20.5%). Salmonella Dublin was generally associated with lower indicator microorganism concentrations compared with other Salmonella serotypes as a group. Relative to other Salmonella, Salmonella Dublin was associated with season (more common in spring) and smaller sample size in boneless and ground beef. Decreased log SPCs and log coliforms were associated with Salmonella Dublin presence in boneless beef, but not in ground beef. Differential associations between Salmonella Dublin and other serotypes with indicator microorganisms were strong enough to cause confounding and suggest that the presence of Salmonella Dublin needs to be accounted for when evaluating indicator performance to assess Salmonella risk in boneless and ground beef.

Original languageEnglish (US)
Pages (from-to)628-636
Number of pages9
JournalJournal of food protection
Issue number4
StatePublished - Apr 1 2020

Bibliographical note

Funding Information:
The authors thank the boneless and ground beef vendors described in this report, the staff at AMS-designated laboratories and at the FSIS Eastern Laboratory for sample analysis, and Bruce Alexander, Jeff Bender, and Scott Wells for technical support. Support for this project was provided by the Pew Charitable Trusts.

Publisher Copyright:
Copyright Ó, International Association for Food Protection


  • Salmonella serotype Dublin
  • Beef
  • National School Lunch Program
  • Animals
  • Cattle
  • Escherichia coli/isolation & purification
  • Meat Products/microbiology
  • Serogroup
  • Colony Count, Microbial
  • Food Microbiology
  • Lunch
  • Salmonella/isolation & purification

PubMed: MeSH publication types

  • Journal Article


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