Long-term Trends in the Incidence of Enterohemorrhagic Escherichia coli and Salmonella on Beef Trim and Ground Beef

Introduction: The contamination of beef products with pathogenic bacteria is of public health concern.  Beef processing plants have programs in place to reduce the occurrence of enterohemorrhagic E. coli (EHEC) and Salmonella. While there is seasonal variation in the incidence of these pathogens, we might hope that over a period of years, the frequency with which they are present would decrease due to continuous improvement in HACCP-based plant mitigation programs. 

Purpose: To determine if there are significant changes in the occurrence of EHECs and Salmonella in beef trim and ground beef over a multi-year period.

Methods: During 10 calendar years (2005-2014), samples of beef trim from 31 processing plants were screened for the presence of EHECs and Salmonella using a PCR-based test.  As the overall frequency of confirmed pathogen-positive samples is very low, we used data from the screening method.  A total of 6,405,553 samples were tested.

Results: Of the 6,202,919 trim samples tested, 483,957 (7.8%) and 201,939 (3.3%) EHEC and Salmonella samples, respectively, were screen-positive. For 202,634 ground beef samples the corresponding positive samples and rates were 9426 (4.7%) and 32,949 (16.3%).  During this period, EHEC in trim increased from 3.3% in 2005 to 4.9% in 2014 (P < 0.05) with a peak of 12.1% in 2012.  The frequency of Salmonella in trim increased from 2.3% in 2005 to 4.5% (P < 0.05) in 2014.  During the same period in RGB, EHEC increased from 0.3% to 8.5% in 2010 and decreased to 2.1% in 2014.  Salmonella increased from 0.3% to 25.3% in 2011 but declined to 11.6% in 2014.  

Significance: The frequency of screen-positive samples for EHECs and Salmonella, especially in ground beef, has significantly increased over this 7-year period suggesting that mitigation programs have not consistently improved.