Listeria represents the third most significant fatal bacterial pathogen transmitted through food within the United States, with expectant individuals bearing an inequitable proportion of this health crisis. Nevertheless, the scientific frameworks employed for establishing food safety regulations have seldom been conceptualized with pregnant populations as a primary consideration. A recent investigation, slated for publication in the journal Risk Analysis, endeavors to rectify this oversight.
Annually, an estimated 1,250 Americans are afflicted with listeriosis, the illness instigated by the Listeria monocytogenes bacterium. This ailment is characterized by an exceptionally high hospitalization rate of 86% and a mortality rate hovering around 14%. For pregnant individuals, the ramifications are considerably more severe: pregnancy-associated listeriosis constitutes 14% of all diagnosed cases, and when the pathogen infects the fetus, it results in stillbirth in a quarter of these instances. Many expectant mothers experience only attenuated, flu-like symptoms, or remain asymptomatic, while the bacterium insidiously traverses the placental barrier. Recent documented outbreaks between 2021 and 2023, linked to products such as ice cream, queso fresco, and enoki mushrooms, tragically led to five stillbirths within a mere three-year span.
Researchers Tyler Stump, Carly Gomez, Ph.D., and Jade Mitchell, Ph.D., affiliated with Michigan State University, embarked on a mission to address this critical research void. By meticulously examining animal studies that documented the maternal host’s response to specific dosages of L. monocytogenes, the team successfully formulated novel, biologically credible dose-response models. These models, one designed for maternal infection and another for stillbirth risk, are grounded in data derived from guinea pigs and gerbils, species exhibiting crucial biological similarities to humans concerning Listeria pathogenesis.
The findings of this study indicate that the presence of fetal brain infection serves as a more precise and dependable predictor of stillbirth risk compared to relying solely on direct stillbirth outcomes. Fetal brain involvement was observed in every instance of stillbirth and was absent in all cases that did not result in stillbirth, establishing it as a verifiable surrogate endpoint that substantially enhanced the model’s predictive accuracy. By integrating this data with existing stillbirth datasets, the researchers achieved a more robust and accurate model than previously accessible.
Public health organizations ought to leverage models tailored to specific demographics, such as these, when formulating food safety directives, rather than applying generalized population estimations. As Listeria outbreaks persist, the availability of more refined risk assessment instruments will facilitate the implementation of more judicious and protective food safety strategies.
Jade Mitchell, Ph.D., Professor, Department of Biosystems and Agricultural Engineering, Michigan State University
The investigators emphasize that pregnancy encompasses a unique confluence of physiological, behavioral, and clinical complexities that cannot be adequately represented by simply adapting models designed for the general immunocompromised population. Their research advocates for public health bodies to adopt population-specific analytical frameworks when developing edicts on food safety pertinent to vulnerable cohorts.
Current guidelines from the FDA advise pregnant individuals to abstain from consuming high-risk foodstuffs, including unpasteurized cheeses, raw sprouts, deli meats, hot dogs, and smoked seafood, unless they are thoroughly heated. Listeria stands apart from many foodborne pathogens owing to its capacity to proliferate even under refrigerated conditions, underscoring the paramount importance of meticulous food handling practices. The manifestation of listeriosis symptoms, such as fever, muscular discomfort, nausea, and diarrhea, can emerge anywhere from one day to several weeks post-exposure.
