Listeriosis is an infection caused by the bacterium Listeria monocytogenes, primarily acquired through consuming contaminated food. This organism is highly resilient, capable of thriving even in cold environments, such as inside a refrigerator. While rare in the general population, listeriosis poses a high risk to vulnerable groups, including adults over 65, individuals with weakened immune systems, and pregnant women. When a pregnant person contracts the infection, the risk of severe complications, including miscarriage, stillbirth, or life-threatening illness in the newborn, increases significantly.
Transmission Through Breast Milk
The current medical consensus is that breast milk is generally not a significant route for the transmission of Listeria monocytogenes from an infected mother to her infant. The infection is systemic, spreading through the bloodstream, but it rarely leads to an active infection of the mammary gland tissue itself. Therefore, the bacteria are not typically found in the milk in concentrations high enough to pose a risk. Although transmission has been documented in isolated human cases, the rarity of these instances suggests that the bacteria are not readily shed into the milk supply. For this reason, a maternal listeriosis diagnosis does not automatically require the cessation of breastfeeding, provided the mother is receiving appropriate medical treatment.
How Infants Acquire Listeria
Infants usually acquire Listeria through two distinct pathways related to the pregnancy and birth process. The most common route is transplacental transmission, where the bacteria cross the placenta from the mother’s bloodstream into the fetal circulation while the infant is still in the uterus. This congenital listeriosis can have devastating consequences, often leading to premature birth, severe systemic infection, or fetal death. The second high-risk route is perinatal transmission, which occurs during delivery. Exposure happens if the mother has a high bacterial load in her birth canal or if there is an ascending infection after the rupture of amniotic membranes.
Symptoms of Listeriosis in Mothers and Newborns
Symptoms in Mothers
The presentation of listeriosis differs markedly between the mother and the newborn. For pregnant women, the infection often manifests as a mild, flu-like illness that can be easily mistaken for a common cold or gastrointestinal distress. Symptoms may include a fever, muscle aches, headache, and sometimes digestive issues like diarrhea.
Symptoms in Newborns
Despite the mother’s mild symptoms, the infection can be severe for the fetus or newborn, as the bacteria can cause widespread damage. In newborns, listeriosis can present with life-threatening complications such as meningitis or sepsis, a severe blood infection. Signs of infection can be subtle, including listlessness, poor feeding, fever, or difficulty breathing, all of which require immediate medical attention.
Prevention Strategies and Breastfeeding Safety
Food Safety Prevention
Preventing listeriosis centers on strict adherence to food safety guidelines, especially for pregnant individuals. A core strategy is avoiding foods known to harbor Listeria monocytogenes. This includes:
- Unpasteurized milk and dairy products.
- Soft cheeses such as Brie, Feta, Camembert, and queso fresco, unless confirmed to be made with pasteurized milk.
Ready-to-eat foods like deli meats, hot dogs, and cold cuts should be thoroughly reheated to an internal temperature of 165°F until steaming hot before consumption. Preventing cross-contamination is also important, which involves washing hands, utensils, and cutting boards after handling uncooked meats. Keeping the refrigerator temperature at or below 40°F helps to slow the growth of contaminating Listeria bacteria.
Breastfeeding Management
If a mother is diagnosed with listeriosis, immediate antibiotic treatment is administered to protect both her health and that of the infant. Healthcare providers generally recommend continuing to breastfeed during and after treatment because the risk of transmission through milk is minimal. If a mother must be separated from her infant or is too ill to nurse, she can usually pump her milk. The pumped milk can often be fed to the infant, though this decision should be made in consultation with the medical team managing her care.