Analysis

Pregnant Women & Listeria: CDC Data Show High Rate of Infections for Expectant Moms

Data collected by the U.S. Centers for Disease Control and Prevention's (CDC) Foodborne Diseases Active Surveillance Network (FoodNet) reveal a disturbingly high rate of Listeria infections among pregnant women—nearly 13 times higher than the general population. From 2004 through 2009, more than one-third (385) of Listeria infections during pregnancy occurred among Hispanic women.

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Listeria infections are rare but can lead to serious complications during pregnancy, including miscarriage or stillbirth, premature labor, and life-threatening illness in newborn infants. Pregnant women can protect their babies by learning what foods to avoid and how to safely prepare and store foods that have a higher risk of Listeria contamination.

Most people diagnosed with Listeria infections require hospital care, and about 1 in 6 die. This dangerous bacterium has been found in processed meats (such as deli meats, hot dogs, and meat spreads), raw (unpasteurized) milk, soft cheeses, smoked seafood, and some kinds of fresh produce. In 2011, Listeria contamination of cantaloupes sickened 147 people in 28 states, and resulted in a reported 33 deaths and one miscarriage.

See graph below: "Incidence of Listeria Infections"

Foodborne diseases have been known to disproportionately affect children and the elderly, but expectant mothers are at a particularly higher risk for Listeria infection because their immune systems are weaker during pregnancy.  Additionally, fetuses and newborns are at increased risk for Listeria infections because Listeria can cross the placenta.  Although pregnant women typically only experience mild flu-like symptoms from the foodborne illness, fetuses and newborns often have severe infections because their immune systems are not fully developed.  

According to a CDC article published in June 2012 in the journal, Clinical Infectious Diseases, nearly one-in-three cases of Listeria infections in pregnant women resulted in fetal loss or neonatal death from 2004 to 2009. Among those newborns with infections, 44 percent were stricken by meningitis, an inflammation of the membranes covering the brain and spinal cord that can result in hospitalization, neurological damage and death.

In addition, the new CDC information points out that Hispanic women are at an even higher risk, likely due to dietary habits. The research determines that although it is not possible to specifically identify the product that caused the infections, there is high consumption of foods connected to past Listeria outbreaks, such as “Mexican-style cheeses,” which are cited in 58 percent of cases involving Hispanic pregnant women versus 16 percent of non-Hispanic pregnant women.

Most Listeria cases are sporadic, not part of recognized outbreaks

A foodborne outbreak occurs when two or more people get the same illness from the same contaminated food or drink. According to the CDC foodborne outbreak database, between 2004 and 2009, there were 15 U.S. foodborne outbreaks caused by Listeria, resulting in 98 illnesses, 73 hospitalizations and nine deaths.

29%

The proportion of Listeria infections during pregnancy that ended in miscarriage, stillbirth or neonatal deaths from 2004 through 2009.

Over the course of the same six years, FoodNet, which conducts surveillance of a series of foodborne diseases including Listeria and represents just 15 percent of the U.S. population, identified 762 sporadic cases of infection (isolated illnesses that were not linked to an outbreak). Out of 760 cases with information available, more than 90 percent of the victims were hospitalized.

Sporadic cases and outbreaks are only the tip of the iceberg. CDC estimates that nearly 1,600 Listeria illnesses are contracted each year in the United States due to exposure to this bacterium in foods. The underdiagnosis is due in part to the fact that laboratory tests do not always detect the organism.  Similarly, miscarriages or neonatal deaths caused by this infection may go undiagnosed.

According to CDC estimates, 19 percent of related deaths caused by foodborne illness could be attributed to Listeria, making it the third most deadly disease-causing bacteria, behind only Salmonella and Toxoplasma gondii

Surveillance and control of Listeria in foods

Established in 1995, FoodNet is a collaborative program among CDC, 10 state health departments, the U.S. Department of Agriculture's Food Safety and Inspection Service (USDA-FSIS) and the U.S. Food and Drug Administration (FDA). FoodNet personnel located at state health departments regularly contact clinical laboratories to get reports of infections diagnosed in residents of these areas; by doing so, FoodNet is able to identify all Listeria cases (even cases that are not part of any recognized outbreak). This information is extremely important to better quantify the impact of foodborne illnesses in the United States, monitor trends over time, identify how and which foods are causing illnesses and disseminate information that can lead to improvements in public health practice and the development of interventions to reduce the burden of foodborne illness.

Foods linked to Listeria infections:

  • Unpasteurized (raw) milk
  • Products made from unpasteurized milk
  • Soft cheeses
  • Processed meats (such as deli meats, hotdogs, and meat spreads)
  • Smoked seafood
  • Certain raw fruits and vegetables (such as cantaloupes)

In addition to FoodNet, CDC has a special surveillance program, called the Listeria Initiative, to aid in the investigation of Listeria outbreaks. Through this initiative, a standardized questionnaire is used to interview any Listeria patient reported to state public health departments.

By using a standardized questionnaire, interviewing patients as soon as they are diagnosed, and ensuring that all Listeria strains are tested to identify their DNA fingerprint, more outbreaks are detected. Data generated by outbreak investigations help identify the contaminated food source responsible for illnesses and can guide industry practices and government policy decisions.

Although Listeria-related infections decreased from 1989 through 2000, no similar improvement has been seen since. This lack of progress has occurred despite industry and government efforts to curb illnesses related to ready-to-eat meats (e.g., deli meats and other foods that do not require cooking).  The lack of any reduction in Listeria-related infections since 2000 suggests that improved industry and regulatory strategies are needed.

Visit the CDC's Listeria website and CDC's Spanish Listeria website to learn more about the recent findings concerning Listeria.



Incidence of Listeria Infections

FSP_listeria-graph-760

This graph was compiled using data provided by the CDC.