Incidence of Pathogens in Retail Sprouts and Other Foods

Research Note: Incidence of Enterohemorrhagic Escherichia coli, Escherichia coli O157, Salmonella, and Listeria monocytogenes in Retail Fresh Ground Beef, Sprouts, and Mushrooms

Journal of Food Protection: Vol. 69, No. 2, pp. 441-443.

M. SAMADPOUR,a M. W. BARBOUR,a T. NGUYEN,a T.-M. CAO,a F. BUCK,a G. A. DEPAVIA,a E. MAZENGIA,a P. YANG,a D. ALFI,a M. LOPES,a and J. D. STOPFORTHa aInstitute for Environmental Health, Inc., Seattle, Washington 98155, USA

MS04-432: Received 14 September 2004/Accepted 22 July 2005


The objective of this study was to determine the prevalence of enterohemorrhagic Escherichia coli (EHEC), E. coli O157, Salmonella, and Listeria monocytogenes in retail food samples from Seattle, Wash. A total of 2,050 samples of ground beef (1,750 samples), mushrooms (100 samples), and sprouts (200 samples) were collected over a 12-month period and analyzed for the presence of these pathogens. PCR assays, followed by culture confirmation were used to determine the presence or absence of each organism. Of the 1,750 ground beef samples analyzed, 61 (3.5%) were positive for EHEC, and 20 (1.1%) of these were positive for E. coliO157.Salmonella was present in 67 (3.8%) of the 1,750 ground beef samples. Of 512 ground beef samples analyzed, 18 (3.5%) were positive for L. monocytogenes. EHEC was found in 12 (6.0%) of the 200 sprout samples, and 3 (1.5%) of these yielded E. coli O157. Of the 200 total sprout samples, 14 (7.0%) were positive for Salmonellaand none were positive for L. monocytogenes. Among the 100 mushroom samples, 4 (4.0%) were positive for EHEC but none of these 4 samples were positive for E. coliO157. Salmonella was detected in 5 (5.0%) of the mushroom samples, and L. monocytogenes was found in 1 (1.0%) of the samples.

Note from the SproutNet

This article gives the impression that about one out of every 5 1/2 packs of sprouts in the area of Seattle Washington contains some sort of contamination.  But critical information is left out.

The article never says what kind of sprouts these were.  It never says what kind of mushrooms either.  For all we know, they might have been brussels sprouts and psilocybin.  The article never says when the research was done.

The internet indicates that Mansour Samadpour is the owner and President of Institute for Environmental Health, inc. ( The others appear to be employed by Dr Samadpour.

I contacted Dr Samadpour and explained that the scientific community agrees that although sprouts can get contaminated in many ways, the pathogens in sprouts from nearly all previous outbreaks have come from the seed.

I asked him what types of sprouts were tested.  He responded that he thought they were alfalfa sprouts.

I let him know that we sample and test as many as 880 samples in a trailer-load of seed as they arrive, and have done this with millions of pounds of seed.  We have only found pathogens a few times. We grow sprouts commercially and, like other sprout growers, test the run off water from every single sub-batch we produce, which is over a hundred tests per week.

Alfalfa sprouts are the most tested vegetable in the world.  Tennessee and the states around us have been testing sprouts off the shelf each and every week for several years.  They have yet to find any of the pathogens that this group claims are prevalent on sprouts.

I was privileged to review the sprout data collected by the State of Florida from 1999 to the end of March 2005.  They conducted 731 tests on a wide variety of sprouts pulled off the shelf.  Again, there were no positives for these pathogens.

The USDA has started pulling sprouts for testing.  According to the USDA Monitoring Programs Office nothing has turned up positive.

None of these organizations have found any of the pathogens Dr. Samadpour so readily detected.

So what went wrong?

Dr. Samadpour responded that possibly the discrepancy was because the research was done in 1999.  That makes a HUGE difference.  Not many growers were testing in 1999 and seed screening was in its infancy.

An argument could also be made that January through March of 1999 saw an alfalfa sprout outbreak of Salmonella Mbandaka involving two sprout growers.  But only 19 people got sick in the entire State of Washington, and there was no mention of this in Samadpour’s article.

His sampling was not explained.  Possibly they went to a store and bought 17 cases during the outbreak, which came from one of the growers involved.  Or possibly they bought a bulk case and pulled 200 samples from it.  But that does not explain finding the 3 samples of 0157 or 12 samples of EHEC.  It also doesn’t explain why the hospitals of Washington were not inundated with poison victims.

The mushroom industry has not initiated the sampling and testing that sprout growers do.  If Samadpour’s sampling and testing was representative of the industry, mushrooms would be killing people as we speak.

Dr. Samadpour said he was aware of the changes the sprout industry has made, but he is concerned about the mushroom industry.  If he was aware of the changes in the industry, don’t you think it would have been nice to inform the reading audience that research was done in 1999?

Many in the sprouting industry already distrust the government and scientific community.  This article is certain to widen the gap.  It has the potential to do great damage to the sprout industry in the US and abroad.

The press may pick up on this Journal of Food Protection article.  If it does, your local news station may contact you as a sprout grower.  I hope this SproutNet gives you some insight that might help you discuss it with them.

Feedback (from the above article in the SproutNet of February 15, 2006).

Dear Bob

“I think the JFP paper can be used to the sprout industry advantage… it could be used as evidence on how much the sprout industry has improved. Surveys by the FDA, OMAFRA and UK FSA have illustrated the high microbiological quality of sprouts in general.”



Dear Bob

“The carriage rate on beef and mushrooms were also relatively high which could mean a high number of false positives… it is surprising the paper got through the peer review process.”



Dear Bob

“It was not clear whether the PCR tests used were validated for sprouts.  As presented in the article, further culture confirmation for E. coli O157 indicated that two out the three PCR positives turned out to be negative.  That is a 67% false positive rate!


Questions can also be raised regarding the tests used for the confirmation of Salmonella.  It was not clear whether the second PCR assay that the authors used to confirm the colonies picked out from the MacConky plates (which is not very selective) has been validated, or whether this second PCR assay was the same as the first one. If yes, most likely this second PCR assay would not be able to reveal anything different from those already shown by the first PCR assay done on the pre-enriched samples.”



Dear Bob,

“Care has to be taken with the selective media used. In our early studies we found a significant number of false positives.”



Dear Bob,

“Being an old timer I’m not totally comfortable with PCR data unless protocols are very carefully developed and followed.”


 Dear Bob,

“The methods used to confirm E. coli, Salmonella and Listeria were suspect. The E. coli PCR was based on stx gene (eaeA is in all E. coli) with a positive being recorded of one or both stx gene was recovered. It is established that a range of E. coli contain stx but don’t actually produce the toxin.  This has led to some to consider the prevalence of E. coli O157 in cattle is over-estimated. In addition, the immuno-test was known to produce a significant number of false-positives.

The Salmonella confirmation test was PCR as opposed to serology or other biochemical tests. PCR was also used to confirm Listeria. These are not the AOAC approved methods and I am surprised this wasn’t noticed when the script was reviewed by the JFP.

If sprouts were brought loose then it is possible that the sprouts were cross-contaminated at the point of sale. However, the authors don’t seem to have considered such a possibility?”


Dear Bob

“Very inflammatory information in the article and very likely there are multiple issues/errors with that work…surprised it got through the approval process.  Unfortunately, even if the information is wrong I expect you will see this information creep into food safety risk assessment summaries around the planet as one more piece of evidence pushing up the food safety risks associated with sprouts (and mushrooms).


Although we have a limited number of samples tested…we have not seen numbers nearly that high in Canada.”


 Dear Bob

“Saw your article and thought you made a number of good points. …the results point to similar levels on all produce.


Regarding the testing done in 1999, this procedure of PCR followed by grow out is still in development BUT is likely to be much more sensitive to low numbers of cells, cells that are entrapped in biofilm and cells that do not slag off in effluent liquid. The procedures in use in most testing facilities today are generally not as sophisticated as was used in the 1999 paper. …the level of sensitivity is under great pressure to be enhanced as the USDA/FDA sense widened threats to the general public (their prime directive).


I’m a bit disappointed that they did not include chicken and fish.  Then everything would appear better.  Instead of constantly hunting for the needles we need ways to sanitize the haystack.”


Dear Bob,

“Thanks again for all of your heads up. If this study represented the sprout industry pre 1999, there would have clearly been more than 20 outbreaks to that point in time. I believe the true message of the study is that other forms of produce currently represent a far greater danger than sprouts, [considering] chlorination and testing.”


Dear Bob

“…the main weakness of the study was the fact it was performed in 1999, the confirmation tests were not in accordance with AOAC methods and the possibility that the positive sprout samples could have been taken as part of the outbreak investigation (i.e. not randomly selected)”.



Bob’s Soapbox

The year 1999 was the worst in history for US sprout related outbreaks.  It saw outbreaks of salmonella spp., Mbandaka, Typhimurium, Saintpaul, Muenchen, and Enteritidis PT4.  Unfortunately, Samadpour’s report does not type out the salmonella, so we can’t connect it to any of these outbreaks.  The FDA reported no sprout related outbreaks involving E coli O157 in 1999.


Had it not been for the 67% false positive rate, one could conclude that Samadpour’s testing procedures could possibly have been accurate, if his sampling procedures were not.  The paper does not adequately describe how or when the sprouts were sampled.


To summarize the article,

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.


It is unfortunate that the author did not inform the readers of the date this research was done.   Had that been included, and had it been reasonably undertaken and documented, it could have shown how far the sprout industry has come since 1999.  I suspect that nearly all food regulators subscribe to the Journal of Food Protection and many of them may assume the work is current.  It is a shame the JFP did not better review this article before it was published.  The sprout industry will pay for their carelessness.