How Dangerous Is Listeria? What Clinicians and Consumers Need to Know About Recent Outbreaks

Rare, deadly, and difficult to treat, listeria infections (aka listeriosis) are among the most serious foodborne infections in the US. Approximately 1,600 Americans become infected with Listeria monocytogenes each year, and about 260 die from it.1 Outbreaks have been linked to an alarmingly long and expanding list of ready-to-eat foods, including: supplement shakes, pasta meals, ice cream, raw milk, leafy greens, bean sprouts, mushrooms, meat slices, dairy products like cheese, packaged salads, cooked chicken, hard‐boiled eggs, pork products, frozen vegetables, packaged caramel apple, and soya products.²

The most recent outbreak (reported this month) is a multistate, multiyear event linked to requeson—a soft cheese like ricotta—manufactured by Clover Hill Dairy, LLC, of Mechanicsville, MD. Nine cases across 3 states have been reported so far, with 8 hospitalizations and 1 death. The earliest cases appear to be from March 2023. Investigations by the FDA are ongoing, the product has been recalled, and experts warn that more products may be involved. Just 3 months prior, a case of fatal neonatal listeriosis linked to raw milk was reported in New Mexico.

Listeria infections can be particularly devastating for pregnant women, newborns, older adults, and people with weakened immune systems. In recent years, outbreaks have become more frequent, following a familiar pattern: a contaminated product enters the food market, reaches unsuspecting consumers, and causes illness before investigators can identify its source and remove it from circulation. This trend demonstrates the pressing need to take precautions and informed action to prevent infections, detect them early, and institute proper control measures.

Listeriosis is caused by Listeria monocytogenes, a bacterium found in the soil, water, decaying vegetation, and digestive tracts of animals and birds. It has an uncanny ability to survive and multiply at extremely cold temperatures that would kill or inactivate other bacteria. With listeria, refrigerating perishable foods does not provide all the protection people expect it to.³

The bacteria typically get into food during processing. The bacteria form biofilms on food, making them hard to remove despite standard procedures. Even when removed during a heating step that usually precedes refrigeration, listeria can recontaminate food just before packaging. A 2025 review confirmed that Listeria continues to trigger outbreaks and the recall of certain ready-to-eat foods even when existing regulatory standards are followed.⁴

“Listeria behaves differently from many foodborne bacteria because it is not a question of a contaminated ingredient entering a system. It is often about persistence inside the environment itself. It can survive in wet areas and drains, as well as in many different parts of a facility that are difficult to clean. Once it's there, it persists and spreads at a rate that can be very hard to contain,” says Mario Hupfeld, cofounder and chief technology officer at NEMIS Technologies, who holds a doctoral degree in microbiology and molecular biology and helped bring to market a rapid, onsite pathogen detection platform for environmental monitoring of listeria and other foodborne pathogens.

“So, if it is only discovered after it reaches the finished product, then the opportunity to stop it earlier has already been missed, and it will continue to infiltrate new environments. This is also why outbreaks look sudden from the outside. Inside the system, they are usually the result of something that has been present for a fairly long time but went undetected,” he adds,

In healthy adults, listeriosis is rarely fatal. The bacteria are limited to the gut because the immune system keeps them in check. Symptoms last only a few days and include fever and muscle aches. nausea, vomiting, and diarrhea. However, for pregnant women, newborns, and people who are immunocompromised, listeriosis can be fatal.⁵ In these groups, the infection isn’t limited to the gut but becomes invasive listeriosis, where generalized infection affects the entire body, causing sepsis, meningitis, rhombencephalitis, endocarditis, and even focal infections like abscesses.

Pregnant women are twenty times more likely to contract listeriosis. Listeria can cross the placental barrier and reach the growing fetus in the womb, causing miscarriage, stillbirth, or a life-threatening infection such as meningitis in the newborn baby.⁶ The growing fetus can experience damage even when the mother doesn’t show severe symptoms of listeria infection. In some cases, the mother recovers fully yet still gives birth to a critically ill newborn.

In older and/or immunocompromised patients, their immune system may not be able to keep listeria limited to the gut, leading to invasive listeriosis. The mortality rate for invasive listeriosis ranges from 11% to 60%. A meta-analysis found that primary bacteremia, central nervous system complications, alcoholism, chronic kidney disease, cardiovascular disease, pulmonary disease, and cancer significantly increase the risk of death. ⁷

In early 2025, a deadly multistate listeria outbreak linked to a supplement shake occurred. Manufactured by Prairie Farms Dairy in Fort Wayne, Indiana, and distributed to hospitals and care facilities across the country, the shakes resulted in the death of 14 people across 21 states.⁸ Investigators traced the origins of the outbreak to unsanitary environmental conditions at manufacturing facilities, as far back as 2018. Undetected, the contaminated shakes had been infecting people for years.

Another outbreak linked to pasta meals produced by Oliveri Foods followed soon after. From mid-2024 to 2025, it claimed 6 lives and infected people across 18 states. Using whole-genome sequencing, investigators found that it was caused by contaminated precooked pasta sold by grocery brands. The median age of affected patients was 74 years. 75% of those affected were women, and the youngest was a 4-year-old.⁸

“Early symptoms are often nonspecific,” says Shelby Marquardt, MD, founder and chief creative officer of Blue Sky Scrubs. “Clinicians should keep a low threshold for considering Listeria in high-risk patients with fever, myalgias, or gastrointestinal symptoms, especially if there is a history of consuming higher-risk refrigerated ready-to-eat foods or a known recall exposure. Blood cultures are the mainstay of diagnosis for invasive disease. If meningitis or encephalitis is suspected, cerebrospinal fluid studies and cultures are important. Stool testing is generally not useful for diagnosing listeriosis,” they add.

Listeria outbreaks are harder to identify and contain because of the disease’s protracted incubation period. Symptoms of listeriosis can show up the same day or take as long as 10 weeks. Thus, common source cases may occur at largely different times, some occurring early and others weeks apart. The bacteria’s ability to survive in refrigerated environments compounds this dilemma, as it means a batch of contaminated food can continue reaching customers for months after it exits the production line.¹⁰ Even the CDC’s PulseNet system, which detects outbreaks relatively faster by using whole-genome sequencing to match bacterial strains, often lags by a few weeks.

Fortunately, listeriosis is treatable with intravenous ampicillin alone or in combination with gentamicin when treatment is commenced early.¹¹ However, Listeria is resistant to cephalosporins, which is the go-to medication used in treating other kinds of meningitis. The difference between treatment success and failure lies in how early treatment is initiated. Late treatment has a bad prognosis, especially for immunocompromised people.

The responsibility of preventing listeria outbreaks does not rest on individuals alone. Since the bacteria contaminate food, it requires a multilevel approach. Individuals, food providers, regulators, institutions, agencies, and governments must work together to achieve effective prevention and control.¹² The NEMIS kit developed by Maria and his team and similar innovations should be encouraged.

Everyone is advised to ensure that ready-to-eat foods are properly processed before consumption. Or better still, avoided, especially during active outbreaks. Since ready-to-eat foods don’t need to be cooked before they are consumed, they are the most Listeria-linked category of food. Heat kills listeria; to destroy it in food, heat the item to an internal temperature of 165°F (74° C) or until it is thoroughly steaming hot.¹³

Individuals at high risk of listeriosis, such as pregnant women and immunocompromised individuals, are advised to take extra precautions or avoid ready-to-eat foods that carry a higher risk of contamination, such as deli meats, soft cheeses, and pre-made salads. Check FDA and CDC recall notices regularly.

The supplement shake outbreak clearly shows what happens when lapses occur in the food chain that supplies food to health care facilities. There is a strong need to investigate all food procurement processes to ensure better food safety, as vulnerable patients deserve at least as much safety as the general public, if not more. Clinicians should report Listeria cases to the relevant authorities, and recalls on implicated foods should be initiated promptly.

References

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2. Mohapatra RK, Mishra S, Tuglo LS, et al. Recurring food source-based Listeria outbreaks in the United States: An unsolved puzzle of concern?. Health Sci Rep. 2024;7(2):e1863. Published 2024 Feb 4. doi:10.1002/hsr2.1863

3. Bento D, Tobin EH. Listeria monocytogenes Infection (Listeriosis). 2026 Apr 12. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan–. PMID: 30521259.

4. Yangchen J, Sarkar D, Rood L, Vaskoska R, Kocharunchitt C. Listeria monocytogenes: A Continuous Global Threat in Ready-to-Eat (RTE) Foods. Foods. 2025 Oct 27;14(21):3664. doi: 10.3390/foods14213664. PMID: 41227636; PMCID: PMC12607602.

5. Shang L, Xiang W, Lun M, Qu S, Yin Y, Xu Y, Zhou Y, Zhu P, Song Y. Recent Advances in Host Immune Mechanisms Against Listeria monocytogenes Infection. J Inflamm Res. 2025 Aug 11;18:10821-10833. doi: 10.2147/JIR.S535302. PMID: 40823352; PMCID: PMC12356216.

6. WHO. Listeriosis. Accessed June 23, 2026. https://www.who.int/news-room/fact-sheets/detail/listeriosis

7. Huang, Chienhsiu, et al. “Mortality Risk Factors Related to Listeriosis — a Meta-Analysis.” Journal of Infection and Public Health, vol. 16, no. 5, 1 May 2023, pp. 771–783, www.sciencedirect.com/science/article/pii/S1876034123000941, https://doi.org/10.1016/j.jiph.2023.03.013.

8. Outbreak Investigation of Listeria monocytogenes: Frozen Supplemental Shakes. FDA. February 2025. Accessed June 23, 2026. https://www.fda.gov/food/outbreaks-foodborne-illness/outbreak-investigation-listeria-monocytogenes-frozen-supplemental-shakes-february-2025

9. Deadly multistate Listeria outbreak tied to prepared pasta meals expands. 2025. CIDRAP. October 31, 2025. Accessed on June 23, 2026. https://www.cidrap.umn.edu/listeria/deadly-multistate-listeria-outbreak-tied-prepared-pasta-meals-expands

10. Serrano-Heredia SM, et. al. Survival of Listeria monocytogenes biofilms and planktonic cells on cooked ham in a contamination-storage-digestion process. Int J Food Microbiol. 2025 Nov 2;442:111346. doi: 10.1016/j.ijfoodmicro.2025.111346. Epub 2025 Jul 12. PMID: 40682994.

11. Bento D, Tobin EH. Listeria monocytogenes Infection (Listeriosis) [Internet]. StatPearls - NCBI Bookshelf. 2026. Available from: https://www.ncbi.nlm.nih.gov/books/NBK534838/

12. Alegbeleye O, Rhee MS. Growth of Listeria monocytogenes in fresh vegetables and vegetable salad products: An update on influencing intrinsic and extrinsic factors. Compr Rev Food Sci Food Saf. 2024 Sep;23(5):e13423. doi: 10.1111/1541-4337.13423. PMID: 39169547.

13. Bolívar A, Pérez-Rodríguez F. Listeria in Food: Prevalence and Control. Foods. 2023 Mar 24;12(7):1378. doi: 10.3390/foods12071378. PMID: 37048199; PMCID: PMC10093824.