Listeria monocytogenes is the third leading cause of death from a bacterial foodborne pathogen in the United States, and pregnant people bear a disproportionate share of the burden. However, the scientific models used to develop food safety policy are rarely designed specifically with pregnant people in mind. A new study published in the journal Risk Analysis aims to change that.
Each year, approximately 1,250 Americans contract listeriosis, the disease caused by Listeria monocytogenes. The hospitalization rate for this disease is a staggering 86%, and approximately 14% of cases are fatal. For pregnant people, the risk is even higher. Pregnancy-related cases account for 14% of all listeriosis cases, and when Listeria monocytogenes reaches the fetus, 25% of those infections cause stillbirth. Many pregnant women experience only mild flu-like symptoms or no symptoms at all, but the bacteria quietly cross the placenta. Recent outbreaks linked to ice cream, queso fresco, and enoki mushrooms from 2021 to 2023 resulted in five stillbirths in just three years.
Researchers Tyler Stamp, Dr. Carly Gomez and Dr. Jade Mitchell. Researchers at Michigan State University set out to fill this gap. By analyzing animal studies that tracked how pregnant hosts responded to specific doses of Listeria monocytogenes, the research team developed a new biologically plausible dose-response model (one for maternal infection and one for stillbirth) built on data from guinea pigs and gerbils, which share with humans key biological traits related to Listeria pathogenesis.
This study found that fetal brain infection was a more accurate and reliable indicator of stillbirth risk than direct stillbirth outcomes alone. Fetal brain infection was present in all observed stillbirths and absent in all non-stillbirth cases, making it a testable surrogate endpoint that greatly strengthens the accuracy of the model. By pooling this data with other stillbirth datasets, the researchers created a model with a better fit than previously available models.
Public health agencies should use these population-specific models when developing food safety guidance, rather than applying general population estimates. As Listeria monocytogenes outbreaks continue, more accurate risk assessment tools would support more informed and protective food safety policies. ”
Dr. Jade Mitchell, Professor, Department of Biological Systems and Agricultural Engineering, Michigan State University
The authors caution that pregnancy involves a unique combination of physiological, behavioral, and clinical variables that cannot be captured by the application of common immunocompromised population models. Their initiative calls on public health agencies to use population-specific models when developing food safety guidelines for sensitive groups.
FDA guidance recommends that pregnant people avoid high-risk foods such as unpasteurized cheese, raw sprouts, deli meats, hot dogs, and smoked seafood unless thoroughly cooked. Listeria is rare among foodborne pathogens because it can grow even under refrigeration, so it is especially important to handle food carefully. Symptoms of listeriosis, such as fever, muscle aches, nausea, and diarrhea, can appear anywhere from one day to several weeks after exposure.
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Risk Analysis Society
