On Behalf of the Emerging Infectious Disease Taskforce
Recent listeria contamination has led to several food recalls and new cases of the illness. The pathogen poses significant risks to pregnant women, fetuses, the elderly, and immunocompromised individuals. The following is additional information regarding the illness from TeamHealth’s Emerging Infection Disease Taskforce.
Listeria Monocytogenes
Listeria monocytogenes is a versatile, gram-positive bacterium commonly found in soil, water, and decaying vegetation. It can endure extreme conditions like freezing, high salinity, and acidic environments, making it particularly resilient.
Unlike most foodborne pathogens, listeria can grow at standard refrigerator temperatures, posing a risk in ready-to-eat foods. This ability to thrive under refrigerated conditions can lead to high bacterial counts in contaminated foods, which increases the likelihood and severity of infection. The resistance of listeria to common food safety measures underscores the seriousness of its contamination.
Cellular “Tricks” of Listeria
Listeria can transition from a highly invasive, flagellated form to a less mobile, non-flagellated form that is more persistent in the body. At lower temperatures, listeria is very mobile, using flagella for movement through tissues. It also induces actin polymerization, facilitating intracellular movement and invasion. However, as temperatures rise toward 95-98.6°F (35-37°C), its mobility decreases. However, as it becomes less mobile, it becomes more resistant and can persist in tissue.
Listeria often concentrates in the placenta and placental fluids. Listeria can cross the placenta to the fetus and the blood-brain barrier. It can also persist in the gut, leading to fecal shedding and environmental contamination.
Listeria Case Incidence
The United States sees about 0.24 cases of laboratory-confirmed listeriosis per 100,000 people annually, with approximately 800 reported cases each year. However, the actual number of cases, including asymptomatic or mild ones, may exceed 1,600 annually, often going undiagnosed. Listeria is the third leading cause of death from foodborne illness in the U.S., causing around 260 deaths per year. Most diagnosed cases require hospitalization, with a case-fatality rate of 20%. Over 25% of pregnancy-associated cases result in fetal loss or newborn death. The CDC ranks Listeria as the 3rd most common cause of death from food poisoning.
Sources of Listeria
Listeria is typically acquired through contaminated food except for fetal and neonatal infections, which occur via in utero transmission or exposure during delivery. Rare cutaneous infections can affect veterinarians or livestock workers. High-risk foods include soft cheeses (e.g., brie, camembert), cold meats, paté, soft serve ice cream, melons, pre-prepared salads, raw seed sprouts, and unpasteurized dairy products. Pregnant Hispanic women are at increased risk due to dietary habits involving soft cheeses like queso fresco, often made from unpasteurized milk.
The Clinical Presentation of Listeriosis
The clinical features of listeriosis vary with many healthy individuals experiencing mild or asymptomatic infections. In these cases, listeria can cause a self-limited acute febrile gastroenteritis, but routine stool cultures often miss the diagnosis unless linked to a known outbreak.
Invasive listeria infections, more common in immunocompromised individuals, can present as sepsis, meningitis, or meningoencephalitis. Focal infections such as septic arthritis, osteomyelitis, and infections of prosthetic grafts, as well as intrathoracic, intra-abdominal, ocular, and cutaneous sites, are also possible.
High-risk Populations for Listeria
The primary high-risk populations for listeria include:
- The elderly and neonates
- Immunocompromised individuals
- Pregnant women – especially Hispanic women
- Pregnant women are 10 times more likely than other people to get listeria infection. Pregnant Hispanic women are 24 times more likely than other people to get listeria infection.
- Professionals and laborers with routine exposure to animal products of conception
Diagnosis of Listeriosis
Listeriosis is diagnosed based on clinical symptoms and exposure history, confirmed through blood, CSF, or urine cultures. Stool cultures and serology are not useful, but listeria can be detected in placental fluids, meconium, or gastric secretions, especially in newborns.
Management of Listeria Exposures and Infections – Non-pregnant
Clinicians often need to manage individuals exposed to listeria-contaminated food. The CDC provides guidelines for non-pregnant individuals, though they are based on limited scientific data. The American College of Obstetricians and Gynecologists (ACOG) offers similar recommendations, with specific considerations for pregnancy, maternal-fetal health, and neonatal concerns.
General Exposure and Management Principles for Listeria
Management should be tailored to each patient based on their risk profile, exposure type, setting, and clinical presentation, with consultation from an infectious disease specialist recommended.
Listeria Exposure – Afebrile Without Symptoms
For asymptomatic individuals exposed to listeria, testing or treatment is generally not recommended, even for high-risk individuals. Patients should be informed about listeriosis symptoms and advised to seek evaluation if symptoms like fever, flu-like symptoms, or myalgia develop within 60 days. Immunocompromised and elderly individuals should be especially vigilant for CNS infection symptoms.
Listeria Exposure – Afebrile with Mild Symptoms
For high-risk individuals with mild symptoms, conservative management can be considered. Testing is usually not indicated, but blood cultures should be obtained. Oral antibiotics like ampicillin, amoxicillin, or TMP-SMX are recommended by some clinicians. However, there is no scientific evidence supporting their effectiveness against listeria.
Listeria Exposure with Fever or Findings of Possible Invasive Disease
Patients with fever or signs of invasive listeriosis should be admitted, tested, and treated with intravenous ampicillin and gentamicin for 14 to 21 days. This includes critical care if needed, blood cultures, and lumbar puncture if neurological symptoms are present. Infectious disease and public health consultations are also recommended.
Delayed Exposure Follow-up
For patients presenting 28 to 60 days after exposure, testing or treatment is typically not recommended if asymptomatic. Management should follow guidelines for recent exposures, with monitoring for symptoms up to 60 days post-exposure.
Positive Blood or Other Cultures
Patients with positive blood cultures should be admitted immediately, regardless of symptoms. Initial treatment involves intravenous ampicillin and gentamicin, with other specific therapies as advised by infectious disease consultants. Cephalosporins should never be used for treating listeriosis.
Listeriosis during Pregnancy
Listeriosis in pregnant women may present with mild symptoms but often leads to serious fetal outcomes, including miscarriage, stillbirth, and preterm labor. Pregnant women are significantly more susceptible to listeriosis, with Hispanic women being at higher risk.
Listeriosis in the Neonate
Listeriosis during pregnancy can result in severe outcomes for the neonate, including sepsis, meningitis, or preterm labor. Specific information on neonatal listeriosis is available in the references.
Key Takeaways for Listeria Management and Reporting
Listeria, the third most common cause of fatal foodborne infections in the U.S., demands clinician awareness, especially regarding high-risk populations and pregnant women. Diagnosis involves a combination of exposure history, symptoms, and cultures, with prompt antibiotic treatment using ampicillin and gentamicin. Cephalosporins are ineffective against listeria and should not be used. Listeriosis is a reportable disease, and consultations with infectious disease and public health professionals are essential.
Learn more about TeamHealth’s Emerging Infectious Disease Taskforce (EIDT) and see a full list of references.