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    Product Testing, Part 10: What do you test for, and what might it mean?

    Tuesday, March 8th, 2011

    Julia Stewart:
    Hello, this is Julia Stewart, and welcome back to PMA’s audio blog, “Ask Dr. Bob” with PMA’s Chief Science & Technology Officer Dr. Bob Whitaker. We’re continuing to talk about the benefits and challenges in product testing. Bob, there is a tremendous amount of product testing going on today in some commodities. What are some of the things we should consider when looking at all this testing and the resulting data?

    Bob:
    I think there are three basic questions we need to ask about testing, as well as what this data may mean and what we might do with it:
    1. What pathogens should we be testing for?
    2. Does a positive test result necessarily mean that the product would cause disease? And,
    3. How can a company use the data generated for product testing programs to improve its food safety program?

    First, let’s take the question “What pathogens should we be testing for?” Today, you’ll find many companies who test for E. coli O157:H7 and Salmonella species – others add a test for nterohaemorrhagic E. coli or EHECs – meanwhile still others are beginning to look at shigatoxin-producing E. colis or STEC’s – and a few even include Listeria monocytogenes in their product testing protocols.  Meanwhile, there are still some who look for indicator species like generic E. coli or total coliforms, even though the correlation between these and actual pathogen contamination is questionable in produce. 

    So, which organisms should we test for?  A producer needs to make the decision on what to test for based on the risk profile of the particular products they grow and produce, the timing window they have between testing and when they need to ship, and the costs involved.  It’s important to avoid a “one size fits all” approach.  Instead, we should employ a science- and risk-based approach to determine commodity-specific and/or pathogen-specific testing strategies. 

    For example, let’s say we’re a tomato grower. Then we’d clearly want to prioritize testing for Salmonella species, since this pathogen is most commonly associated with tomatoes.  On the other hand, if we are a leafy greens grower, then we’d want to broaden the pallet of tests to include Salmonella and E. coli O157:H7 and perhaps consider adding EHEC or STEC’s to cover all pathogenic strains historically associated with these foods. 

    Julia:
    So let’s look at the second question: Does a positive test result mean the product would cause disease? 

    Bob:
    You can look at this question from a number of perspectives.  Clearly, the most important is public health.  The Food, Drug and Cosmetic Act – that’s the federal food safety law we in the produce industry are currently subject to – considers product that tests positive to be adulterated, and prevents that product from being put into commerce.  The Food and Drug Administration will always act first and foremost to protect public health.  Further, as of September 2009, you have the obligation to report any products that may pose a public health risk via the Reportable Food Registry – so, if you had a positive test result and the product is in the marketplace, you’d need to report that to FDA. 

    From a strictly scientific perspective, we know that new strains of E. coli have emerged in the last 30 years, most notably, E. coli O157:H7; and, unlike its harmless brethren, as few as 10 cells of O157:H7 can cause significant health issues in a person, particularly children, the elderly or other at-risk populations. Conversely, we can now identify more than 2,000 strains of Salmonella, whose illness-causing dose rates are much higher than with E. coli O157:H7, if they cause human illness at all.  Also, Salmonella infection is generally not lethal, and we’re learning that Salmonella may be more common in the environment than originally thought. 

    So, while the zero-tolerance approach currently mandated by the FD&C Act is appropriate for a pathogen such as E. coli O157:H7, today’s science may or may not justify such a strict standard for other, perhaps less harmful pathogens.  We’re also starting to understand that perhaps a positive PCR test result or even a bacterial culture may not necessarily correlate to that organism’s ability to cause human illness.  Research is showing that our screening for DNA fragments that are associated with the pathogen’s ability to produce toxin, or to attach to the intestines, might not by themselves be proof that the organism can cause disease.  Other factors such as the pathogen’s acid tolerance and the physiological state of the pathogen likely play a critical role. 

    Julia:
    So, how can the data generated by a product testing program be used?

    Bob:
    Obviously, enacting a product testing program is an important decision and a significant financial commitment.  So, it seems reasonable that a company that chooses to do product testing should look to use the resulting data to improve their food safety programs.  In order to do that, you must have procedures in place to receive testing data from lab partners, to store and sort that data, and then analyze the data so that trends can be identified and acted upon.  For instance, you may be able to use product testing data in conjunction with additional data from your GAP or HACCP programs to identify and prioritize specific risk factors.  As an example, a preharvest risk assessment that identifies an animal intrusion event has occurred may be used in conjunction with a concentrated in-field product testing program to verify if the intruding animal species carried a pathogen, and perhaps even what buffer zone distances are necessary to manage the potential risk. 

    Julia:
    Bob, you’ve raised some interesting issues here to consider when setting up product testing programs.  How much data from product testing do you think is out there in the industry?

    Bob:
    Julia, that’s difficult to say.  Right now, the clear focus has been in leafy greens crops.  Some companies have large, sophisticated product testing programs that have generated thousands of data points.  In the last year there’s been a great deal of discussion around how industry might combine some of this data or “mine” it to see if it’s possible to prioritize risks.  We talked about this with FDA during a meeting after the Center for Produce Safety’s research symposium in June.  Sometime in the near future, we should do a blog series on data mining, as it’s a subject all unto itself with a number of positive and negative aspects.

    Julia:
    That sounds good, Bob; I’ll hold you to it!  Speaking of holding you to it, I promised our listeners that as we concluded this blog series, you’d sum up the real value of product testing.  So next time in our final blog in this series, let’s summarize some of the discussions we have had on this subject and see what the plusses and minuses are.  Until then, thank you, listeners, and we’ll see you back here next time.

     
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