The University of Georgia Center for Food Safety conducted an exclusive interview with epidemiologist Elaine Scallan Walter. After releasing her groundbreaking research in 2011, which has been cited over 10,000 times, she comes back in 2025 with a continuation of it with new findings. The 2025 update to landmark foodborne illness research by Scallan Walter reveals an update on the seven most important pathogens causing the most illnesses, hospitalizations, and deaths thus advancing methodology, and updating data resources.
Dr. Scallan Walter
Scallan Walter, a professor of epidemiology at the Colorado School of Public Health, emphasized that the latest estimates focused on pathogens responsible for the majority of foodborne illnesses, hospitalizations, or deaths in previous estimates. These include norovirus, Campylobacter spp., Clostridium perfringens, invasive Listeria monocytogenes, nontyphoidal Salmonella, Shiga toxin-producing Escherichia coli (STEC), and Toxoplasma gondii.
Methodology
“Rather than delay the research because of the COVID-19 pandemic response, we focused on the seven that are causing the majority of illnesses, hospitalizations, or deaths,” Scallan Walter said in an interview with the University of Georgia Center for Food Safety.
The new methodology builds on previous work in 2011, while incorporating new data sources. One major improvement was the use of healthcare administrative data to more accurately estimate the total number of noroviruses. “In 2011, we relied on a pretty crude approach for norovirus… now we can use U.S-based outpatient visit data to refine estimates,” she said.
Incorporating the most recent data and more refined approaches improved estimating underdiagnosis. “Accounting for underdiagnosis is critical,” she said. “We know not everyone seeks care at the same rate, so we used bloody diarrhea as a marker of severity in 2011.”
That method evolved in 2025, she said, to include demographic and symptom factors based on FoodNet population survey data and FoodNet surveillance data. “Instead of relying on this one symptom as a marker of severity, we looked at demographic and symptom factors to estimate the rate of underdiagnosis,” Scallan Walter said. “The addition of others resulted in larger multipliers for these pathogens.”
Previously, a multiplier of two was used to account for underdiagnosis among hospitalized cases. The latest study partnered with the Marshfield Clinic in Wisconsin to analyze actual stool sample submission rates in hospitals. “It creates a more data-driven approach,” she said. “Which was not too far off the mark of doubling, again validating. But we would much prefer to be data-driven rather than relying solely on assumptions from subject matter experts.”
Scallan Walter’s 2011 research has been cited more than 10,000 times. She has authored over 100 academic papers and received the 2021 Rosalind Franklin Society Award in Science for her work on foodborne illness estimation.
Advice for future researchers
New researchers entering the academic and professional field of food safety are eager to learn and succeed. Scallan Walter offered advice on how newcomers can achieve success in the growing field.
For the new researchers, she offered advice rooted in versatility and cross-disciplinary engagement. “Food safety touches everything — microbiology, epidemiology, agriculture,” she said. “It’s priceless to see all sides of it.” She continued, “One of the neatest things about our research is that it requires input from so many different disciplines.” Each discipline works to ensure quality food for the public.