During the past two years the Listeria bacteria has garnered a great amount of press due to the recall of Blue Bell Ice Cream in 2015 and last month's mass recall of frozen veggies circulated by CRF Frozen Foods.
Although food recalls may seem sudden, they tend to be the culmination of years' worth of surveillance. Public health officials map illnesses across the country and watch carefully for patterns in bacterial agents, food sources, distributing companies, and other data. In most cases, pinpointing an exact moment of contamination is very difficult.
May's recall of frozen vegetables was due to an eight person pattern of infection over the last three years with a likely link to a single distributer.1
Scientists first realized that Listeria was linked to food intake in 1981 when an outbreak in Canada was linked to cabbage consumption. Since, other outbreaks have been linked to milk, uncooked soft cheeses, and ready-to-eat meats.2
Listeria is a fairly common bacteria that rarely causes serious infection in humans unless there are preexisting medical conditions. However, it has been known to have devastating effects on pregnancy. Also, during pregnancy a part of the woman's immune system is suppressed to prevent rejection of the baby which also causes an increase in her susceptibility to this infection.
3 A pregnant woman who has acquired the infection is not generally in any mortal danger herself, but Listeria infections in babies are often severe and can be fatal.
Based on the results of a collaborative study between Stanford University Medical Center and the University of California Berkeley, scientists determined that the placenta does a noteworthy job of protecting the infant from Listeria acquired by the mother, but that if even one bacteria manages to break through its barriers, the placenta then becomes a significant hub for infection.4 In this situation, complications such as preterm labor, miscarriage, stillbirth, or infection of a newborn during the birthing process have been known to occur.
Due to this, physicians recommend that a pregnant woman abstain from raw or undercooked meats completely and only consume pasteurized dairy products. In the past, the FDA advised avoiding all soft cheeses, but has fairly recently changed its position to only recommend abstinence from cheeses made from raw/unpasteurized milk.5 Although ready-to-eat meats have been known to carry Listeria, the risk is extremely low as long as they are properly heated. Patients are generally advised to avoid them only if outbreaks become a problem in their area. A gestating mother needs a varied nutrient-rich diet to sustain a pregnancy. Avoiding too many food items is far riskier than the chance of infection.
If infection is known to occur, your physician can prescribe antibiotics to protect your baby. However, it is best to follow the guidelines listed above to limit the risk of exposure as no symptoms may arise despite the infection being present.
To help reduce the risk in all individuals the FDA and CDC have recommended the following:
"All produce should be rinsed before consumption even if it will be peeled. A scrub brush should be used on all firm items, like melons and gourds. These should then be dried with a clean cloth or paper towel. Also, uncooked meats should be kept apart from veggies to prevent the transmission of bacteria during preparation. Always wash your hands before and after food preparation and clean countertops and utensils after use. Freezer temperatures should at or below 0°F (≈-17°C) and refrigerator temperatures at or below 40°F (≈4°C)."
The following links provide more information and the latest updates to the FDA and CDC's guidelines: