Listeria infection during pregnancy is rare. About 1 in 25,000 pregnant women in the United States contract listeriosis each year, according to the CDC. But pregnant women are roughly 13 times more likely to get it than the general population, which is why it gets so much attention in prenatal care. The infection is uncommon, but the consequences when it does occur can be severe.
Why Pregnant Women Face Higher Risk
During pregnancy, your immune system deliberately dials back one of its key defense systems. Normally, your body fights bacteria like listeria using a type of immune response that targets infected cells directly. But this same response can also threaten the pregnancy by attacking the fetus, which your body recognizes as partially foreign. To protect the pregnancy, your immune system shifts away from this cell-targeting mode and toward a different strategy better suited to fighting threats outside of cells.
The problem is that listeria is an intracellular pathogen, meaning it hides inside your cells. The very immune tools your body suppresses during pregnancy are the ones most effective against it. Pregnant women produce lower levels of the signaling molecules that activate these defenses, while producing higher levels of molecules that actively dampen them. This creates a window of vulnerability that lasts throughout pregnancy.
Who Is Most Affected
Not all pregnant women face equal risk. Data from ACOG shows that pregnancy-associated listeriosis is markedly more common among Hispanic women, at a rate of about 8.9 per 100,000, compared to 2.3 per 100,000 among non-Hispanic women. This disparity likely reflects differences in dietary patterns, particularly the consumption of fresh soft cheeses like queso fresco, which are a well-documented source of listeria contamination even when made with pasteurized milk.
What Listeria Feels Like During Pregnancy
Listeriosis in pregnant women typically causes fever, muscle aches, and fatigue. It can look almost identical to the flu, which makes it easy to dismiss. Unlike in non-pregnant adults, where listeria can progress to headache, stiff neck, confusion, or seizures, pregnant women often experience only the milder symptoms. That’s partly why it can go unrecognized.
The incubation period matters here. If you eat contaminated food, intestinal symptoms like nausea or diarrhea can show up within 24 hours and pass within a few days. But the more dangerous invasive form of the illness, where the bacteria enter your bloodstream, typically takes about two weeks to develop symptoms. That gap between exposure and illness can make it hard to trace back to a specific food.
The Stakes for the Baby
The real concern with listeria during pregnancy isn’t what it does to you. It’s what it does to the pregnancy. Nearly 25% of pregnancy-associated listeriosis cases result in fetal loss or death of the newborn. Listeria can cross the placenta and infect the fetus directly, potentially causing miscarriage, stillbirth, premature delivery, or life-threatening infection in the newborn.
This is the core tension: the infection itself is rare, but when it happens, the outcomes can be devastating. That combination of low probability and high severity is why food safety guidelines for pregnancy are so cautious about it.
Foods That Carry the Highest Risk
Listeria is unusual among foodborne bacteria because it can grow at refrigerator temperatures. Most bacteria slow down or stop multiplying in cold environments, but listeria keeps going. This means that even properly refrigerated foods can become increasingly contaminated the longer they sit. Keeping your refrigerator at or below 40°F (4°C) slows growth but doesn’t stop it entirely.
The FDA specifically recommends that pregnant women avoid:
- Deli meats, hot dogs, and luncheon meats unless reheated until steaming hot
- Soft cheeses like queso fresco, queso blanco, and requesón, whether made from pasteurized or unpasteurized milk
- Unpasteurized milk and any foods made with it
- Refrigerated smoked seafood like lox, kippered fish, or smoked salmon, unless cooked into a dish like a casserole
- Refrigerated pâtés or meat spreads
The queso fresco warning is worth highlighting because it applies even to versions made with pasteurized milk. The cheese’s high moisture content and low acidity make it a particularly hospitable environment for listeria, which can contaminate the product after pasteurization during processing.
How It’s Diagnosed and Treated
If your doctor suspects listeriosis, the standard test is a blood culture. This involves drawing blood and checking whether listeria bacteria grow from it. Stool cultures aren’t useful for diagnosis, and blood tests that look for antibodies against listeria are unreliable. The diagnosis depends on actually finding the bacteria in your blood or, in more severe cases, in spinal fluid.
When caught, listeriosis is treatable with antibiotics. Early treatment can protect the baby, which is why the diagnosis matters. If you’re pregnant and develop a fever with flu-like symptoms that you can’t explain, particularly within a few weeks of eating a high-risk food, mention the possibility of listeria to your healthcare provider. A blood culture is a straightforward test, and starting antibiotics early makes a meaningful difference in outcomes.
Putting the Risk in Perspective
At 1 in 25,000, your individual odds of getting listeriosis during pregnancy are low. To put that in context, roughly 3.6 million babies are born in the U.S. each year, meaning listeriosis affects an estimated 144 pregnancies annually. You are far more likely to develop gestational diabetes or preeclampsia than to contract listeria.
But the food precautions exist because they’re simple and the downside of infection is so serious. Reheating deli meat, skipping the queso fresco, and keeping your fridge cold are low-effort steps that effectively eliminate most of the risk. The infection is rare in part because these guidelines work.