Queso fresco, a soft, fresh cheese, is a popular food item that poses a significant health risk during pregnancy. The concern stems from the potential presence of a bacterium that can cause severe illness, especially in pregnant individuals. This risk is primarily linked to how soft cheeses like queso fresco are traditionally made and handled. Because of this potential for contamination, health authorities advise pregnant individuals to avoid this cheese unless specific safety criteria are met.
The Primary Health Concern: Listeria monocytogenes
The danger in queso fresco comes from the bacterium Listeria monocytogenes, which is common in soil, water, and animal feces. This pathogen contaminates food and is particularly concerning because it is a psychrotroph, meaning it can grow even in refrigerated temperatures. Soft cheeses are a frequent vehicle for Listeria due to their high moisture content, near-neutral pH, and low salt levels, which create an ideal environment for the bacteria to thrive.
The primary risk factor is the use of unpasteurized milk, as pasteurization is a heating process designed to kill harmful bacteria like Listeria. Even when commercially produced with pasteurized milk, soft cheeses remain a concern due to the high potential for post-pasteurization contamination. Contamination can occur if the processing environment harbors the bacteria, allowing it to multiply during the product’s refrigerated shelf life. This vulnerability has made soft Hispanic-style cheeses a frequent source of listeriosis outbreaks in the United States.
Unique Risks of Listeriosis During Pregnancy
Pregnant individuals are more susceptible to listeriosis, the infection caused by Listeria monocytogenes, due to changes in their immune system. They are estimated to be 10 to 20 times more likely to contract listeriosis than other healthy adults. Although the mother may only experience mild, flu-like symptoms such as fever or muscle aches, the infection can have severe consequences for the developing fetus.
The bacteria can cross the placental barrier, directly infecting the fetus. Infection during pregnancy can result in serious outcomes, including miscarriage, stillbirth, or premature delivery. If the newborn survives, the infection can lead to life-threatening conditions such as sepsis or meningitis, potentially causing long-term health issues like developmental delays or intellectual disability. The fatality rate for perinatal listeriosis typically ranges from 20% to 30%.
Guidelines for Safe Dairy Consumption
To mitigate the risk of listeriosis, pregnant individuals should strictly avoid all soft cheeses, including queso fresco, unless their safety can be confirmed. When purchasing soft cheese, check the label for the word “pasteurized” to ensure the milk was treated to kill bacteria. However, even pasteurized queso fresco is generally advised against due to the risk of post-processing contamination.
Harder cheeses, such as Cheddar, Swiss, and Parmesan, are considered safe because their low moisture content and higher acidity inhibit bacterial growth. Soft cheeses made with pasteurized milk, like cottage cheese, cream cheese, and mozzarella, are also safe alternatives. If queso fresco or other soft cheeses are consumed, they must be cooked until steaming hot throughout, reaching an internal temperature of 165°F, as heat destroys the Listeria bacteria.