January 15, 2025

Improved Efficiency for STEC Risk Mitigation 

Over the past few posts and articles, we have put out a couple of briefs about the considerations for STEC/EHEC testing, and overall risk management in the produce industry. STEC/EHEC is a diverse group of organisms, and a major contributor to outbreaks and recalls. While there are notable serogroups (O157, O26, O45, O103, O111, O121, O145) that most frequently lead to outbreaks and illness, many other pathogenic strains are contributing to disease but are not as well known or studied. While the impact and importance of the pathogen group for human health may be clear due to rising amounts of attributable illnesses, less clear is how to address managing it within the food industry.  

One source of confusion originates from method variability – what defines STEC/EHEC positives (toxin(s) + attachment, toxin alone, toxin(s) + attachment + O serogroups), secondary confirmation processes (secondary PCR, IMS + secondary PCR, ddPCR, cultural confirmation) and what they find, and ultimately, what a food producer should react to. Within food testing, it is fair to say that STEC/EHEC represents somewhat of a “choose your own adventure” decision tree. The decision to use shiga toxin (stx1, stx2) and/or intimin (eae) coupled with various options for secondary molecular and cultural confirmation methods can be complicated to say the least, and the most important point is to make sure that the food producer is comfortable and consistent in their choice. It is also advisable to review those choices annually to ensure it continues to align with internal and external risk management expectations.  

Risk-based monitoring – the opportunity to improve food safety 

In the world of diagnostic testing, STEC/EHEC methodology is being researched to improve the detection of the broad group and increase confidence in what a positive result may mean. Often these new assays include the familiar molecular targets, but new targets and approaches are in development to improve confidence and time to result. Given some of the complexities and uncertainties with STEC/EHEC testing (discussed in prior articles), we should expect that screening methods for this organism group may see more change than other pathogens in the coming years. With these new learnings, and enhanced means to detect and culture these organisms (especially environmentally stressed ones), the food testing segment will offer improved options for detection, and more efficient means to remove STEC/EHEC risk from the food supply chain.  

One of the things that excites me in food microbiology is the blend of cutting-edge science and technology with the applied and practical nature of food production. Ideating innovative solutions to optimize risk reduction for consumers and improve food producers’ ability to produce high-quality nutrition for our communities is a critical and valuable effort. While improving food safety is the goal, we also need to be diligent in designing systems that help us achieve that outcome. Pathogen testing in food should be looked at with an eye toward risk management and not pass/fail mentalities – this isn’t exclusive to STEC/EHEC, but that group of organisms is a great example of where that can be particularly relevant even within the testing methodology itself.  For example, Shiga toxin alone (absent eae/intimin) can cause illness and has led to outbreaks. Shiga toxin with the intimin gene is more likely too, and those genes along with the Top 7 O-serogroups is an even greater predictor that the detection may be of clinical relevance. Throw in some additional options for molecular confirmation and culture confirmation, all with their own considerations and limitations, and we have method-driven example of a scenario where certain risks can be eliminated and others intentionally/unintentionally allowed. The critical importance when using a methodology is to make sure as a food producer that you know what the considerations are, and that they align your company’s business and food safety strategies.    

While there may be uncertainty today about what a STEC/EHEC positive test means in product or environmental testing, remember that clinical definitions are very clear – someone can become ill, sometimes fatally so, and that illness can happen irrespective of whether your chosen detection method deems it negative.