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 Listeria and Food Poisoning

Overview

Listeria are bacteria which can cause an infection known as listeriosis. The bacteria are very resistant to common food preservation agents such as heat, salt, nitrite, and acids. It can also multiply in refrigerated foods. Listeria is often present in the intestines of seemingly healthy animals. The bacteria can contaminate milk and meat products produced from infected animals and can also contaminate vegetables fertilized with contaminated manure. Since the early 1980s Listeria infections have been traced to food products such as coleslaw, milk, soft cheeses, hot dogs, and luncheon meats. Pregnant women are advised to avoid foods, such as soft cheeses, that are easily contaminated with Listeria. Taking precautions such as thoroughly cooking foods, eating only pasteurized milk products, washing fruits and vegetables, and washing hands after contact with raw meat also reduces the chances of contracting listeriosis. The federal government has established programs to test for Listeria in ready-to-eat foods and to recall food containing the bacteria. Healthy people are generally resistant to listeriosis but pregnant women are very susceptible to the infection. Listeria infections in pregnant women may result in miscarriages or stillbirths. Meningitis (brain infections) and septicemia (bacteria in the bloodstream) may occur in infants born to women with listeriosis.

Description of Listeria

According to the Centers for Disease Control and Prevention (CDC 2008) "Listeriosis, a serious infection caused by eating food contaminated with the bacterium Listeria monocytogenes, has recently been recognized as an important public health problem in the United States. The disease affects primarily persons of advanced age, pregnant women, newborns, and adults with weakened immune systems. However, persons without these risk factors can also rarely be affected. The risk may be reduced by following a few simple recommendations." Listeria monocytogenes is found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer.

Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin such as meats and dairy products. The bacterium has been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses and cold cuts at the deli counter. Unpasteurized (raw) milk or foods made from unpasteurized milk may contain the bacterium.

Listeria is killed by pasteurization and cooking; however, in certain ready-to-eat foods such as hot dogs and deli meats, contamination may occur after cooking but before packaging.

Sources of Listeria

According to the Centers for Disease Control and Prevention (CDC 2008) "You get listeriosis by eating food contaminated with Listeria. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy. Although healthy persons may consume contaminated foods without becoming ill, those at increased risk for infection can probably get listeriosis after eating food contaminated with even a few bacteria. Persons at risk can prevent Listeria infection by avoiding certain high-risk foods and by handling food properly."

The CDC estimates that in the United States, 2,500 persons become seriously ill with listeriosis each year. Of these, 500 die. At increased risk are:

  • Pregnant women - They are about 20 times more likely than other healthy adults to get listeriosis. About one-third of listeriosis cases happen during pregnancy.
  • Newborns - Newborns rather than the pregnant women themselves suffer the serious effects of infection in pregnancy.
  • Persons with weakened immune systems
  • Persons with cancer, diabetes, or kidney disease
  • Persons with AIDS - They are almost 300 times more likely to get listeriosis than people with normal immune systems.
  • Persons who take glucocorticosteroid medications
  • The elderly

Healthy adults and children occasionally get infected with Listeria, but they rarely become seriously ill.

Prevention of Listeria infections

Preventative measures can be taken by pregnant women in order to avoid contracting Listeria infections.

General recommendations:

  • Thoroughly cook raw food from animal sources, such as beef, pork, or poultry.
  • Wash raw vegetables thoroughly before eating.
  • Keep uncooked meats separate from vegetables and from cooked foods and ready-to-eat foods.
  • Avoid unpasteurized (raw) milk or foods made from unpasteurized milk.
  • Wash hands, knives, and cutting boards after handling uncooked foods.
  • Consume perishable and ready-to-eat foods as soon as possible.

The Food Safety and Inspection Service (FSIS) and the FDA have established food testing and recall programs to protect the public from Listeria contaminated foods. According to the USDA,

Neither FSIS nor FDA will accept any detectable L. monocytogenes on cooked, ready-to-eat food. This is called "zero tolerance" for the bacteria. Both agencies have testing programs for L. monocytogenes. The goals of these programs is to help government and industry identify the causes of contamination in processing plants and to make permanent changes that will reduce Listeria monocytogenes contamination, prevent problems and ensure a safe food supply. Both agencies can hold or detain products at the food processing plant, request a voluntary recall of the product or seize products through court order if necessary.

Initially, FSIS regulatory testing programs included selected cooked meat products. Following a CDC report that traced the first case of listeria meningitis to incompletely heated turkey franks consumed by a cancer patient, FSIS expanded the L. monocytogenes monitoring program to further prevent the sale of any cooked and ready-to-eat meat or poultry products from which L. monocytogenes is isolated, such as cooked sausages (including frankfurters and bologna), cooked roast beef, cooked corned beef, sliced canned ham, sliced canned luncheon meat, jerky, cooked poultry, and poultry and meat salads and spreads.

When ready-to-eat meat or poultry product is found to contain L. monocytogenes, the plant is notified and the product is subject to detention at the plant, voluntary recall or court-ordered seizure. From 1987 through March 1992, 27 FSIS-regulated cooked products from 27 firms have been recalled, including frankfurters, bologna and other luncheon meat, chicken salad, ham salad, sausages, chicken, sliced turkey breast and sliced roast beef.

FDA's monitoring programs initially concentrated on cheese and dairy products both domestic and imported. Later, FDA expanded coverage to include other ready-to-eat foods such as sandwiches, prepared salads and smoked fish. From 1987 to March 1992, 516 products from 105 firms have been recalled.

The agencies' stepped up monitoring and surveillance programs for L. monocytogenes, and food industry efforts have helped identify intervention measures aimed at controlling the organism.

Listeria infections during pregnancy

Eating contaminated food is the most common way that listeriosis is contracted. The CDC has stated that (CDC 2003), pregnant women "are about 20 times more likely than other healthy adults to get listeriosis. About one-third of listeriosis cases happen during pregnancy."

According to the Centers for Disease control (CDC 2008) "When infection occurs during pregnancy, antibiotics given promptly to the pregnant woman can often prevent infection of the fetus or newborn.

Babies with listeriosis receive the same antibiotics as adults, although a combination of antibiotics is often used until physicians are certain of the diagnosis. Even with prompt treatment, some infections result in death. This is particularly likely in the elderly and in persons with other serious medical problems."

Diagnosis and treatment of Listeriosis

According to the U.S. Department of Agriculture (CDC 2003), "A blood or spinal fluid test (to cultivate the bacteria) will show if you have listeriosis. During pregnancy, a blood test is the most reliable way to find out if your symptoms are due to listeriosis. When infection occurs during pregnancy, antibiotics given promptly to the pregnant woman can often prevent infection of the fetus or newborn. Babies with listeriosis receive the same antibiotics as adults, although a combination of antibiotics is often used until physicians are certain of the diagnosis."  You should contact your health care provider if you have questions, or believe you have eaten a contaminated product or have flu-like symptoms.

Food Safety Guidelines

The Centers for Disease Control (CDC 2008) recommend the following basic guidelines for food handling:

  • Thoroughly cook raw food from animal sources, such as beef, pork, or poultry.
  • Wash raw vegetables thoroughly before eating.
  • Keep uncooked meats separate from vegetables and from cooked foods and ready-to-eat foods.
  • Avoid unpasteurized (raw) milk or foods made from unpasteurized milk.
  • Wash hands, knives, and cutting boards after handling uncooked foods.
  • Consume perishable and ready-to-eat foods as soon as possible.

Contacts for additional information

The following agencies can be contacted for additional information about Listeria:

FSIS

Media Inquires: 202-720-0314
Public Inquires: 202-720-9113, 1-800-535-4555
www.fsis.usda.gov

FDA

Media Inquires: 202-205-4144
Consumer Inquires (CFSAN): 202-205-5004; 1-888-SAFEFOOD
www.cfsan.fda.gov

CDC

Media Inquires: 404-639-3286
Technical questions about listeriosis: Meningitis and Special Pathogens Branch: 404-639-2215
www.cdc.gov/foodsafety

USDA's Meat and Poultry Hotline

1-800-535-4555
In the Washington, DC area, call 202-720-3333

Hotline hours are from 10 a.m. to 4 p.m., Eastern time.


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