A warm welcome to Razieh Sadat Mirmahdi, the latest guest in our FSHN Research Journeys series, which follows graduate students’ research in the Food Science and Human Nutrition program at The University of Florida. Razieh is a second-year graduate student pursuing her Ph.D. in food science. Her research into eliminating norovirus in cooked oysters will allow consumers to enjoy these shellfish without worrying about norovirus infection.
Razieh: When it comes to indulging in the culinary pleasures of the sea, few delicacies are as enticing as a plate of oysters. The briny aroma, the tender texture, and the burst of flavor as you take that first bite can be a true delight for the senses. Yet as you savor the delectable morsel, a question may linger in your mind: Will this plate of oysters make me sick? The answer is: “Possibly yes”!
In recent decades, the US has witnessed many outbreaks linked to consuming raw oysters.3 Logic dictates that cooking oysters is critical to preventing foodborne illnesses. Yet some outbreaks result from cooked oysters.
These incidents suggest a question: why do we encounter foodborne pathogens in cooked oysters? My research endeavors to provide a comprehensive response to this puzzling phenomenon, shedding light on the complexities surrounding the safety of cooked oysters and ultimately contributing to enhancing food safety standards.
Investigating Norovirus in Cooked Oysters
Based on data from the U.S. Census of Aquaculture, the US has witnessed a remarkable surge in oyster consumption. A survey conducted in 2022 showed the most popular oyster preparation method is steaming, with a preference rate of 70.9%. Grilling comes next at 48.4%, followed by raw at 41.9%, and cooked in a recipe alongside other ingredients at 33.4%.1,2 Yet no exact information exists about the specific time and temperature parameters used in these methods in the U.S.
In most cases, applying heat to raw food products effectively reduces the presence of foodborne pathogens to safe levels, rendering the food safe for consumption. For example, the pasteurization of milk involves specific time and temperature parameters. Pasteurization reduces the number of illness-causing bacteria and makes the milk safe to drink. Cooking oysters serves the same purpose and should ensure they are safe for consumption. However, cooking oysters may not eliminate norovirus.
My Ph.D. project is inspired by the startling statistic that approximately 4.5% of norovirus outbreaks linked to oyster consumption between 1971 and 2021 were associated with cooked oysters (fried, baked, and steamed).3 Norovirus is a highly contagious virus causing gastroenteritis, leading to symptoms like vomiting, diarrhea, and stomach cramps.4 In the US, ten norovirus outbreaks were associated with cooked oysters between 2012 and 2017.3
Through my research, I aim to establish effective oyster cooking techniques to mitigate norovirus using a quantitative microbial risk assessment (QMRA) framework. By shedding light on this risk, we will empower consumers and industry alike to make informed choices when considering oyster preparation.
Starting My Journey to Food Virology at UF
After completing my master’s degree, I set my sights on gaining admission to a renowned university for its excellence in food science. My research led me to the University of Florida, a distinguished institution with a strong reputation in my field. Upon closer examination of their faculty’s research, I was captivated by the work of Dr. Naim Montazeri. His research focuses on critical areas such as the survival and inactivation of human norovirus in agricultural systems, encompassing pre- and post-harvest water, soil, and fresh produce.
Food virology holds immense significance in safeguarding public health, preventing foodborne outbreaks, facilitating global food trade, and upholding consumer trust in the safety of their food supply. The field remains ever-evolving and crucial within food safety and security. Dr. Montazeri’s area of expertise deeply resonated with my academic interests, prompting me to initiate contact with him and enroll at UF.
Studying Norovirus Inactivation in Cooked Oysters
Since cooked oysters have been implicated in norovirus outbreaks, our first step involves identifying current cooking practices for oysters in U.S. restaurants by running a survey. We aim to gather comprehensive information regarding the time and temperature parameters used in cooking oysters. Then, I will study the heat inactivation and factors involved in the survival of norovirus in oysters using the time and temperature data acquired from our survey to quantify the survival of norovirus.
In the final step, we will establish a quantitative microbial risk assessment model for norovirus in cooked oysters. This framework will provide insights into the risks associated with the consumption of undercooked oysters. The results will serve as a valuable resource for consumers, stakeholders, and policymakers to mitigate norovirus in oysters and reduce the risk of foodborne illnesses.
Addressing Challenges: Overcoming False Negatives and Using Virus Surrogates
The absence of an effective infectivity assay for human norovirus has necessitated using molecular detection techniques like PCR as the gold standard for its detection and quantification. Human sewage and oyster tissues often contain strong PCR inhibitors, which can reduce amplification efficiencies and produce falsified PCR signals. This inhibition can result in false-negative outcomes when human norovirus concentrations are low. Thus, we will employ appropriate extraction and purification methods to accurately detect and quantify human norovirus in complex matrices.
Additionally, measuring the infectivity of human norovirus in the laboratory has proven difficult. The primary detection method, RT-qPCR, cannot distinguish between infectious and non-infectious particles. Consequently, we are using virus surrogates that mimic human norovirus behavior. Cultivable surrogate viruses offer several benefits. However, surrogates may not fully replicate human norovirus’s structural similarity and environmental persistence.
After this research, we can answer the initial question—will this plate of oysters make me sick? with a resounding “No!” We recommend refraining from consuming raw oysters and advise thorough cooking before consumption. As our risk assessment project progresses, specific guidelines regarding the optimal time and temperature for safely cooking oysters will be provided in the future.
Razieh Sadat Mirmahdi is a second-year graduate student pursuing her Ph.D. in food science, focusing on food virology in the lab of Dr. Naim Montazeri. Beyond her academic endeavors, Razieh holds a master’s level proficiency in preparing traditional Persian dishes. Her skills and passion for fine food have afforded her a unique perspective on the intersection of science and gastronomy.
References
- S. Department of Agriculture. 2019. Census of Aquaculture (2017). Volume 3, Special Studies Part 2. AC-17-SS-2. Washington, DC: U.S. Department of Agriculture, National Agricultural Statistics Service.
- Richardsa S, Vassalosb M, Motallebic M. Factors Affecting Consumer Purchasing Decisions and Willingness to Pay for Oysters in South Carolina. Journal of Food Distribution Research. 2022 Jul;53(2):1-25.
- Centers For Disease Control and Prevention (CDC). Foods that can cause food poisoning. 2022 [cited 2022 Jul 12]. Available from: https://www.cdc.gov/norsdashboard
- Orenstein R. Gastroenteritis, Viral. In: Encyclopedia of Gastroenterology [Internet]. Elsevier; 2020 [cited 2023 Sep 22]. p. 652–7. Available from: https://linkinghub.elsevier.com/retrieve/pii/B9780128012383659731
Looking for more posts exploring graduate research projects in the FSHN Department at the University of Florida?
Dive into the Research Journeys of other graduate students below.
M.S. Food Science
M.S. Nutritional Sciences
Ph.D. Food Science
Ph.D. Nutritional Sciences
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