Food As a Vehicle for Transmission of Shiga Toxin

Food as a Vehicle for Transmission of Shiga Toxin-Producing Escherichia coli

Journal of Food Protection®, Volume 70, Number 10, October 2007 , pp. 2426-2449(24)

Erickson, Marilyn C.1; Doyle, Michael P.2

1Center for Food Safety and Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA 2Center for Food Safety and Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA


Contaminated food continues to be the principal vehicle for transmission of Escherichia coli O157:H7 and other Shiga toxin-producing E. coli (STEC) to humans. A large number of foods, including those associated with outbreaks (alfalfa sprouts, fresh produce, beef, and unpasteurized juices), have been the focus of intensive research studies in the past few years (2003 to 2006) to assess the prevalence and identify effective intervention and inactivation treatments for these pathogens. Recent analyses of retail foods in the United States revealed E. coli O157:H7 was present in 1.5% of alfalfa sprouts and 0.17% of ground beef but not in some other foods examined. Differences in virulence patterns (presence of both stx and stx2 genes versus one stx gene) have been observed among isolates from beef samples obtained at the processing plant compared with retail outlets. Research has continued to examine survival and growth of STEC in foods, with several models being developed to predict the behavior of the pathogen under a wide range of environmental conditions. In an effort to develop effective strategies to minimize contamination, several influential factors are being addressed, including elucidating the underlying mechanism for attachment and penetration of STEC into foods and determining the role of handling practices and processing operations on cross-contamination between foods. Reports of some alternative nonthermal processing treatments (high pressure, pulsed-electric field, ionizing radiation, UV radiation, and ultrasound) indicate potential for inactivating STEC with minimal alteration to sensory and nutrient characteristics. Antimicrobials (e.g., organic acids, oxidizing agents, cetylpyridinium chloride, bacteriocins, acidified sodium chlorite, natural extracts) have varying degrees of efficacy as preservatives or sanitizing agents on produce, meat, and unpasteurized juices. Multiple-hurdle or sequential intervention treatments have the greatest potential to minimize transmission of STEC in foods.


International Specialty Supply

October 30, 2007

Garbage In Garbage Out 

The October issue of the Journal of Food Protection contains an article by Marilyn Erickson and Michael Doyle, from the Center for Food Safety and Department of Food Science and Technology at the University of Georgia.  The abstract includes the following: "Recent analysis of retail foods in the United States revealed E. coli O157:H7 was present in 1.5% of alfalfa sprouts and 0.17% of ground beef but not in some other foods examined." 

The folks at the Center for Good Safety should have known better, and the Journal of Food Protection is, in my book, no longer a credible source of scientific research. Before talking about how the authors got the information, and how JFP came to publish it, let's look at the information itself. 

If 1.5% of all alfalfa sprouts are contaminated with E.coli O157:H7 that would be one contaminated package in each 5 ½ cases that go out of a sprout grower's door.  Interesting, considering that sprouts are the most tested produce in the world. 

The authors must certainly be aware that sprout growers sample and test the runoff water that touches each and every sprout before the products ever make it to market.  Our own sprout company, Sungarden Sprouts, does this and has never found O157:H7 in product that is produced for resale.  These tests verify that each of the ten million plus cups we have processed since we started testing have been negative for O157:H7.   

Sprout growers aren't the only ones testing sprouts.  The USDA Monitoring Programs Office sampled 1512 sprouts pulled from shelves in eleven states in 2006. None were positive for O157:H7.  Florida and some other states have been testing since 1999, yet there has not been a recall on sprouts in the US in over three years. 

But how about just using common sense?  For the sake of agreement, let's take a minimal example.  I don't think anyone would disagree that if you took the average number of packaged sprouts sold in each US state, it would be more than 3000 pounds per state per day.  This is only 1000 twelve packs per state per day.  If 1.5% were contaminated, these 50,000 twelve packs would contain 9,000 contaminated packages (50,000 x 12 units x 1.5%).  Granted, not everyone who eats contaminated product gets sick, but a package of sprouts is about eight servings.  And this figure does not take into account sprouts sold in bulk to restaurants or sprout mixes containing alfalfa (we sell more mixes than straight alfalfa).  So I think we could agree that there would be thousands, if not tens of thousands, of new cases each day if 1.5% of alfalfa sprouts were contaminated with 0157:H7.

If an outbreak is related to sprouts, the vehicle is relatively easy to determine.   The red flags are well staked.  If an outbreak involves mostly women in their thirty's and forties, for instance, epidemiologists scrutinize sprouts, tomatoes, and lettuce.  If there were thousands of new cases each day the epidemiologists would be all over it. 

As aseed company, we sell millions of pounds of alfalfa seed.  For the last eight years we have sampled and tested the seed from each and every bag we have sold in the US.  Although we have found various types of contamination in seed, we have never found O157:H7 in alfalfa seed.  I'm not going to say alfalfa seed is never contaminated.  There have been at least six sprout related outbreaks in the US related to O157:H7 (none from ISS seed).  But six outbreaks in the history of a product do not add up to thousands of contaminated packages consumed daily.  The authors of this article should have known this does not pass the smell test.

Instead, they took this information from M. Samadpour, "Research Note: Incidence of Enterohemorrhagic Escherichia coli, Escherichia coli O157, Salmonella, and Listeria monocytogenes in Retail Fresh Ground Beef, Sprouts, and Mushrooms."  This article, which was criticized in the February 16, 2006 SproutNet, also concluded that 7% of alfalfa sprouts and 5% of mushrooms are contaminated with salmonella.  Some information from the USDA and a bit of quick math indicates this is about 40 million packages of contaminated mushrooms a year.  Do the JFP, Samadpour, and Erickson and Doyle really believe this?

Last year ISS wrote a letter to the JFP Editor pointing out that the article did not state that the sprouts were alfalfa sprouts (and I don't know why Erickson and Doyle concluded that they were).  Nor did it disclose that the research was done in "about 1999" according to a personal conversation with the author.  The letter concluded with the following:   

"It appears that research undertaken by Samadpour and ten of his employees, in which undisclosed varieties of mushrooms and sprouts, sampled using undisclosed procedures, at an undisclosed time, using an unproven and unapproved testing method (which produced 67% false positives), shows that the undisclosed products were contaminated with E. coli O175 and unknown serotypes of salmonella to levels beyond common sense." 

I also warned that the misinformation in the Samadpour article would be repeated in other journals and consumer articles. Erickson and Doyle took it as gospel and passed it on as fact.  JFP should have known better. 

Samadpour, Erickson and Doyle should do their homework and then ask JFP to write a correction.  Last time I pointed out the obvious errors and omissions the Journal remained mute.