Analysis of Data from FSIS Routine and Intensified Sampling Programs for Listeria monocytogenes from Establishments that Produce Ready-to-Eat Products

Introduction:   The U.S. Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS) samples ready-to-eat (RTE) meat and poultry products and processing environments for Listeria monocytogenes (Lm) through routine sampling (RLm) and intensified verification testing (IVT) programs.  RLm sampling is performed routinely at RTE establishments, while IVT is performed in response to positive results from routine testing programs.  A Food Safety Assessment (FSA) is performed along with RLm and IVT to evaluate food-safety controls at the establishment. 

Purpose:   To analyze results from FSIS RLm and IVT sampling programs and to identify possible trends in the data.

Methods:   Samples were collected proportional to establishment size (RLm) or based on investigative needs (IVT).  Products were collected in the final packaged form, and food contact surface (FCS) and non-FCS (NFCS) samples were collected using sterile SpongeSicles^®hydrated with Dey-Engley (DE) broth.  Samples were analyzed using methods in the FSIS Microbiology Laboratory Guidebook. 

Results:   From 2009–2011, 267/31,511 (0.85%) of RLm samples and 199/9,231 (2.16%) of IVT samples were positive.  For RLm, 10/5,170 (0.19%) of product, 64/17,733 (0.36%) of FCS and 193/8,608 (2.24%) of NFCS samples tested positive.  For IVT, 17/1,392 (1.22%) of product, 75/5,034 (1.49%) of FCS, and 107/2805 (3.81%) of NFCS tested positive.  In previous years (2005–2008), 135/16,284 (0.83%) of RLm samples and 486/13,241 (3.67%) of IVT samples were positive. 

Significance:   From 2009-2011, positive samples were highest for the IVT program, likely because an IVT is triggerd by routine positives, indicating possible sanitation issues.  For RLm and IVT programs, positives were highest for NFCS, followed by FCS, and product samples, an expected finding because Lm is an environmental contaminant.  Compared to previous years (2005-2008), positives increased slightly for RLm and decreased for IVT.  FSIS uses results from IVT and RLm along with FSAs to identify food-safety risks in establishments and to help protect public health.