— OPINION —
By Joe Reardon, Senior Director of Food Safety Programs, National Association of State Departments of Agriculture
The American Frozen Food Institute (AFFI) and the International Fresh Produce Association (IFPA), along with FMI – The Food Industry Association (FMI); the National Restaurant Association (NRA); and the National Association of State Departments of Agriculture (NASDA) recently hosted a Food Safety Forum aimed at discussing current detection methods, public health risk considerations, and regulatory policies affecting enteric viruses (i.e., Norovirus and Hepatitis A virus) and protozoan parasites, such as Cyclospora, in foods.
The safety of the food supply is a high priority in the United States. Reports of foodborne outbreaks caused by microbial contamination of fruits and vegetables remain front page news. The presence of enteric viruses and protozoan parasites in the food supply continues to be of concern; however, these pathogens present unique detection challenges as they cannot be cultivated in the lab, unlike bacterial pathogens which can be cultivated.
This issue has become more important as the U.S. Food and Drug Administration has placed an emphasis on determining the prevalence of these microorganisms in fruits and vegetables. An ongoing FDA frozen berries surveillance assignment for enteric viruses uses a molecular (RT-qPCR) test which detects a small fragment of the viral nucleic acid but cannot confirm the presence of the whole viral genome, or an intact virus particle. It also cannot determine whether the viral nucleic acid identified is infectious. Similarly, FDA began sampling select fresh herbs for the presence of Cyclospora cayetanensis, also based on a PCR method, due to the inability to use culture confirmation of this parasite. The FDA PCR method for Cyclospora also cannot determine infectivity.
The forum
The forum was prompted by calls for increased surveillance and testing for these pathogens across the food supply chain, yet key criteria for what constitutes a positive test result are lacking.
This forum attracted more than 400 registrants from multiple sectors of industry, academia, and government. AFFI and IFPA provided an opportunity for an in-depth discussion of the existing science surrounding non-cultivable pathogen detection methods as well as the implications of using current PCR results without validation procedures for regulatory purposes.
The programming included a presentation from Branko Velebit of the Institute of Meat Hygiene and Technology in Serbia on the difficulty of establishing global thresholds for enteric virus sample positivity given the vast array of assay parameters such as specificity, sensitivity, and limits of detection reflected by cycling threshold (Ct) values. Ynes Ortega with the University of Georgia discussed the complexity of detecting Cyclospora, specifically the human pathogen Cyclospora cayetanensis.
Given the differences between these pathogens, scientists should be thoughtful when using current detection methods, and regulators need to use validated methods to ensure confidence in results. Furthermore, this session highlighted the need to establish appropriate sample positivity criteria if new policies, such as zero tolerance for findings of nucleic acid, are going to be the compliance standard used in regulatory surveillance programs.
The second panel was comprised of academic leaders, Lee-Ann Jaykus, North Carolina State University, and Lucy Robertson, Norwegian University of Life Sciences, who shared examples on the limitations of the existing data and knowledge of transmission of enteric viruses and parasites on foods compared to other pathogens. Jaykus and Robertson agreed that it is in the best interest of academia, regulators, and the food industry to acquire data to develop validated risk-based methods to best interpret PCR results, as a positive PCR result does not itself represent a public health risk. Jaykus emphasized the need to establish a risk assessment process, after a confirmed PCR signal, to support a regulatory action, if warranted. Both presenters agreed that appropriate risk-based science should drive policy. Without corroborative evidence, current methodologies can lead to unwarranted regulatory action.
The forum ended with a panel discussion on the public health risk implications of using current detection methods and interpreting results. Representing the National Association of State Departments of Agriculture, I was joined by Tim Jackson of the FDA, Dr. Neda Nasheri of Health Canada, Trevor Suslow of the University of California-Davis, and Sophie Zuber of the Nestle Research Center. This panel presented a robust discussion on the relationship between detecting viral RNA and infectious viruses, the role of modeling and risk assessment, and prevention strategies to control these non-cultivable pathogens. The panel agreed that efforts of academia, industry, and government should focus on prevention to mitigate the risk of food contaminated with enteric viruses or parasites.
Summary
The food industry, academia, regulators, and the public support and expect our food supply to be safe. We also support the use of sound science supporting regulatory goals that accurately and objectively safeguard the food supply. New technological advances can help us to perform our responsibilities better; however, we also need to keep an open mind regarding what roles these new tools provide. When using these PCR methods, absent the ability to enrich and cultivate these organisms, it is currently impossible to confirm that the nucleic acid finding represents the presence of a viable pathogen. Several risk assessment approaches may be applied to augment the validation of potential positive PCR results. Support for PCR as a diagnostic tool exists; its value as a regulatory tool requires further discussion.
The discussions that resulted from this forum were candid and compelling. If you missed the forum, you can watch the session recordings by clicking here. It is evident that differences continue to exist in approaches to enteric virus and parasite testing methodology and interpretation of results, and that we should work collaboratively to enhance the current understanding of the prevalence, risk, and prevention of enteric viruses and protozoan parasites in foods. Perhaps it is time for the food industry, academia, and regulators to consider a holistic approach to provide data that is accurate, reliable, and useful to protect the safety of consumers.
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