Listeriosis

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Listeriosis is a serious infection caused by eating food contaminated with the bacterium Listeria monocytogenes. It is an important public health problem in the United States and other countries. Most people who ingest the Listeria bacteria do not develop symptoms, listeriosis affects primarily persons of advanced age, pregnant women, newborns, and adults with weakened immune systems.

Listeria contamination in Queso Fresco, fresh white cheese. This brand of cheese was recalled in 2007 by the FDA. Source: FDA.

Contents

Other Names

  • Listeria infection

Signs and Symptoms

A person with listeriosis has fever, muscle aches, and sometimes gastrointestinal symptoms such as nausea or diarrhea. If infection spreads to the nervous system, it can cause meningitis, with symptoms such as headache, stiff neck, confusion, loss of balance, sensitivity to light, or seizures. Infected pregnant women may experience only a mild, flu-like illness. However, infections during pregnancy can lead to miscarriage or stillbirth, premature delivery, or infection of the newborn.

Electron micrograph of a flagellated Listeria monocytogenes bacterium, Magnified 41,250X. Source: CDC PHIL

Causes

Listeriosis is caused 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. Listeria monocytogenes is a Gram-positive bacterium, motile by means of flagella. Some studies suggest that 1-10% of humans may be intestinal carriers of L. monocytogenes. It has been found in at least 37 mammalian species, both domestic and wild, as well as at least 17 species of birds and possibly some species of fish and shellfish. The bacteria can be isolated from soil, silage, and other environmental sources. L. monocytogenes is quite hardy and resists the deleterious effects of freezing, drying, and heat even though it does not form spores. Most L. monocytogenes are pathogenic to some degree.

Listeria is an intracellular pathogen, meaning it survives and grows within a person's cells.

Diagnosis

Listeriosis can be a difficult disease to diagnose. The causative organism, Listeria, grows best at low temperatures, unlike most human pathogens, and can often be mistaken for a harmless environmental organism in routine bacterial cultures.

There is no routine screening test for listeriosis during pregnancy, as there is for rubella and some other congenital infections. Pregnant women with symptoms such as fever or stiff neck should consult a doctor. A blood or spinal fluid test will grow the bacteria in culture if it is present. During pregnancy, a blood test is the most reliable way to find out if the symptoms are due to listeriosis.

Early diagnosis and treatment of listeriosis in high-risk patients is critical, since the outcome of untreated infection can be devastating. This is especially true for pregnant women because of the increased risk of spontaneous abortion and preterm delivery. Depending on the risk group, rates of death from listeriosis range from 10% to 50%, with the highest rate among newborns in the first week of life.[1]

Treatment

The risk of an individual person developing Listeria infection after consumption of a contaminated product is very small. If a person has eaten a contaminated product, but does not have symptoms, no tests or treatment may be necessary. However, if the person belongs to a high-risk group and becomes ill with fever within two months of having eaten a contaminated product has eaten a contaminated product, it may be a good idea to contact a doctor.

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 may be serious enough to result in death. This is particularly likely in the elderly and in persons with other serious medical problems.

Chances of Developing Listeriosis

Most cases of listeriosis occur in July and August and result from consumption of contaminated food—typically meat, dairy products, and raw vegetables. Surveys have found the bacteria in 15 to 70% of common fresh food samples. Despite the high prevalence of the bacteria, listeriosis is relatively rare.

In the United States, according to the CDC, an estimated 2,500 persons become seriously ill with listeriosis each year. Of these, 500 die.[2]

At increased risk are[1]:

  • Pregnant women:
    • the risk of listeriosis is about 20 times higher among pregnant women than among nonpregnant healthy adults
    • about one-third of listeriosis cases are diagnosed in pregnant women
    • pregnant women with listeriosis are at increased risk of spontaneous abortion, preterm delivery or stillbirth
  • Newborns
    • mortality among infected newborns is high (50%)
    • newborns are at greater risk of the serious effects of infection
    • listeriosis is not thought to spread through breast milk
  • Elderly people (age ≥ 60 yr):
    • most listeriosis cases occur in the elderly
  • People with weakened immune systems:

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

Prevention

The general guidelines recommended for the prevention of listeriosis are similar to those used to help prevent other foodborne illnesses, such as salmonellosis. In addition, there are specific recommendations for people at high risk for listeriosis.

The following can help prevent listeriosis:

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

In addition to the recommendations listed above, recommendations for people at high risk, such as pregnant women and persons with weakened immune systems, include:

  • Not eating hot dogs, luncheon meats, or deli meats, unless they are reheated until steaming hot.
  • Avoiding getting fluid from hot dog packages on other foods, utensils, and food preparation surfaces, and washing hands after handling hot dogs, luncheon meats, and deli meats.
  • Not eating soft cheeses (such as feta, Brie, and Camembert), blue-veined cheeses, or Mexican-style cheeses (such as queso blanco, queso fresco, and Panela), unless they have labels that clearly state they are made from pastuerized milk.
  • Not eating refrigerated pâtés or meat spreads. Canned or shelf-stable pâtés and meat spreads may be eaten.
  • Not eating refrigerated smoked seafood, unless it is contained in a cooked dish, such as a casserole. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna or mackerel, is most often labeled as "nova-style," "lox," "kippered," "smoked," or "jerky." The fish is found in the refrigerator section or sold at deli counters of grocery stores and delicatessens. Canned or shelf-stable smoked seafood may be eaten.

Epidemiology

Outbreaks

Maple Leaf Foods—Canada, 2008

At least 12 people died in a large Listeria contamination of meat products from the Toronto branch of Maple Leaf Foods, Canada's biggest food company. The company recalled all meat products manufactured at the Toronto facility after the initial reports of deaths.

Northeast US, 2002

A multistate outbreak of Listeria infections with seven deaths and three stillbirths or miscarriages. Theoutbreak was linked to sliceable turkey deli meat. A meat plant, operated by Pilgrim's Pride Foods and located in Franconia, Pennsylvania, recalled 27.4 million lbs. of fresh and frozen ready-to-eat turkey and chicken products on October 12.

Incidence

In the United States, an estimated 2,500 persons become seriously ill with listeriosis each year. Approximately 2500 cases annually in the United States.[3] The vast majority of cases are sporadic, making epidemiological links to food very difficult.[3] Some studies suggest that up to 6% of humans may be asymptomatic intestinal carriers of L. monocytogenes.[4]

Public Health

Policy responses to Listeriosis

Government agencies and the food industry have taken steps to reduce contamination of food by the Listeria bacterium. The Food and Drug Administration and the U. S. Department of Agriculture monitor food regularly. When a processed food is found to be contaminated, food monitoring and plant inspection are intensified. If necessary, the implicated food is recalled.

The Coordinating Center for Infectious Diseases (CCID) is studying listeriosis in several states to help measure the impact of prevention activities and recognize trends in disease occurrence. CCID also assists local health departments in investigating outbreaks. Early detection and reporting of outbreaks of listeriosis to local and state health departments can help identify sources of infection and prevent more cases of the disease.

References

  1. 1.0 1.1 Bortolussi R. Listeriosis: a primer. CMAJ. 2008 Sep 11 Abstract | Full Text
  2. Ramaswamy V, Cresence VM, Rejitha JS, Lekshmi MU, Dharsana KS, Prasad SP, Vijila HM. Listeria--review of epidemiology and pathogenesis. Microbiol Immunol Infect. 2007 Feb;40(1):4-13. Abstract | PDF Full Text
  3. 3.0 3.1 Lynch M, Painter J, Woodruff R., et al. Surveillance for foodborne-disease outbreaks— United States, 1998–2002. MMWR Surveill Summ 2006;55(SS10):1-34. Full Text
  4. Grif K, Patscheider G, Dierich MP, Allerberger F. Incidence of fecal carriage of Listeria monocytogenes in three healthy volunteers: a one-year prospective stool survey. Eur J Clin Microbiol Infect Dis. 2003 Jan;22(1):16-20 Abstract | Full Text.

External Links

FDA, Center for Food Safety and Applied Nutrition, Bad Bug Book: Listeria

Textbook of Bacteriology: Listeria

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