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Listeria Information

What is Listeria?

Listeria monocytogenes (Listeria) is a foodborne disease-causing bacteria; the disease is called listeriosis. Listeria can invade the body through a normal and intact gastrointestinal tract. Once in the body, Listeria can travel through the blood stream but the bacteria are often found inside cells. Listeria also produces toxins that damage cells. Listeria invades and grows best in the central nervous system among immune compromised persons, causing meningitis and/or encephalitis (brain infection). In pregnant women, the fetus can become infected, leading to spontaneous abortion, stillbirths, or sepsis (blood infection) in infancy.

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Image (c) Dennis Kunkel Microscopy, Inc.

Approximately 2,500 cases of listeriosis are estimated to occur in the U.S. each year. About 200 in every 1000 cases result in death. Certain groups of individuals are at greater risk for listeriosis, including pregnant women (and their unborn children) and immunocompromised persons. Among infants, listeriosis occurs when the infection is transmitted from the mother, either through the placenta or during the birthing process. These host factors, along with the amount of bacteria ingested and the virulence of the strain, determine the risk of disease. Human cases of listeriosis are, for the most part, sporadic and treatable. Nonetheless, Listeria remains an important threat to public health, especially among those most susceptible to this disease.

Listeria is often isolated in cattle, sheep, and fowl, and is also found in dairy products, fruits, and vegetables.

What are the Symptoms of Listeria Infection?

It is thought that ingestion of as few as 1,000 cells of Listeria bacteria can result in illness. After ingestion of food contaminated with Listeria, incubation periods (from time of exposure to onset of illness) are in the range of one to eight weeks, averaging about 31 days. Five days to three weeks after ingestion, Listeria has access to all body areas and may involve the central nervous system, heart, eyes, or other locations.

A person with listeriosis usually has fever, muscle aches, and gastrointestinal symptoms such as nausea or diarrhea. If infection spreads to the nervous system, symptoms such as headache, stiff neck, loss of balance, confusion, obtundation (decreased consciousness) or convulsions can occur. With brain involvement, listeriosis may mimic a stroke. Infected pregnant women will ordinarily experience only a mild, flu-like illness; however, infection during pregnancy can lead to miscarriage, infection of the newborn or even stillbirth. Pregnant women are about 20 times more likely than other healthy adults to get listeriosis; about one-third of listeriosis cases happen during pregnancy. The incidence of listeriosis in the newborn is 8.6 cases per 100,000 live births. The perinatal and neonatal mortality rate (stillbirths and early infant deaths) from listeriosis is 80%.

How to Diagnosis and Treat a Listeria Infection?

If you have symptoms of listeriosis, a health care provider can have a blood or spinal fluid test done to detect the infection. During pregnancy, a blood test is the most reliable way to find out if your symptoms are due to listeriosis. If you are in a high-risk group, have eaten the contaminated product, and within 2 months become ill with fever or signs of serious illness, you should contact your health care provider and inform him or her about this exposure. 

There are several antibiotics with which Listeria may be treated. When infection occurs during pregnancy, antibiotics given promptly to the pregnant woman can often prevent infection of the fetus. Babies with listeriosis receive the same antibiotics as adults, although a combination of antibiotics is often used until physicians are certain of the diagnosis.

How to Prevent a Listeria Infection?

General recommendations include: thoroughly cook raw food from animal sources; keep uncooked meats separate from vegetables and from cooked 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; wash raw vegetables thoroughly before eating; and consume perishable and ready-to-eat foods as soon as possible.

Recommendations for persons at high risk, such as pregnant women and persons with weakened immune systems, in addition to the recommendations listed above, include: do not eat hot dogs, luncheon or deli meats, unless they are reheated until steaming hot, and wash hands after handling those products; do not eat soft cheeses (such as feta, Brie, Camembert, blue-veined, or Mexican-style cheese), unless they have labels that clearly state they are made from pasteurized milk; and do not eat meat spreads or smoked seafood from the refrigerated or deli section of the store (canned or shelf-stable products may be eaten).

References

Bennion JR, Sorvillo F, Wise ME, Krishna S, Mascola L. (2008). Decreasing listeriosis mortality in the United States, 1990-2005. Clin Infect Dis. 47(7):867-74.

Bortolussi R. (2008). Listeriosis: a primer. CMAJ. 179(8):795-7.

Bryan, FL. (1999). Procedures to Investigate Foodborne Illness Fifth Edition (p. 119). Des Moines, IA: International Association for Food Protection.

CDC. (2008). Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food—- 10 States, 2007. MMWR Morb Mortal Wkly Rep. 57(14);366-370.

CDC. (2009). Surveillance for foodborne disease outbreaks – United States, 2006. MMWR Morb Mortal Wkly Rep. 12;58(22):609-15.

CDC website. (2009). Listeriosis Information. Retrieved on November 1, 2009 from Centers for Disease Control and Prevention website, http://www.cdc.gov/ncidod/dbmd/diseaseinfo/listeriosis.htm.

Cossart P, Bierne H. (2001). The use of host cell machinery in the pathogenesis of Listeria monocytogenes. Curr Opin Immunol (England). 13(1):96-103.

FDA/CFSAN. (2003). Foodborne Pathogenic Microorganisms and natural Toxins Handbook: The ‘Bad Bug Book.’ College park, MD: Center for Food Safety and Applied Nutrition, Food and Drug Administration. http://www.cfsan.fda.gov/~mow/chap6.html.

Gilbert DN, Moellering RC, Sande MA. (2001). The Sanford Guide to Antimicrobial Therapy 2001. Hyde Park, VT: Antimicrobial, Inc.

Heinitz ML, Johnson JM. (1998). The incidence of Listeria spp., Salmonella spp., and Clostridium botulinum in smoked fish and shellfish. J Food Prot. 61:318-23.

Jurado RL, Farley MM, Pereira E, Harvey RC, Schuchat A, Wenger JD, Stephens DS. (1993). Increased risk of meningitis and bacteremia due to Listeria monocytogenes in patients with human immunodeficiency virus infection. Clin Infect Dis. 17(2):224-7.

Loncarevic S, Tham W, Danielsson-Tham ML. (1996). Prevalence of Listeria monocytogenes and other Listeria spp. in smoked and ‘gravad’ fish. Acta Vet Scand. 37:13-18.

Mayo Clinic. (2009). Listeria infection (listeriosis). Retrieved November 1, 2009 from Mayo Clinic website: http://www.mayoclinic.com/health/listeria-infection/DS00963.

Pinner RW, Schuchat A, Swaminathan B, Hayes PS, Deaver KA, Weaver RE, Plikaytis BD, Reeves M, Broome CV, Wenger JD. (1992). Role of foods in sporadic listeriosis. II. Microbiologic and epidemiologic investigation. JAMA 267(15):2046-50.

Schuchat A, Deaver KA, Wenger JD, Plikaytis BD, Mascola L, Pinner RW, Reingold AL, Broome CV. (1992). Role of foods in sporadic listeriosis. I. Case-control study of dietary risk factors. JAMA. 267(15):2041-5.

Silver HM. (1998). Listeriosis during pregnancy. Obstet Gynecol Surv. 53:737-740.

Tappero JW, Schuchat A, Deaver KA, Mascola L, Wenger JD. (1995). Reduction in the incidence of human listeriosis in the United States. Effectiveness of prevention efforts. JAMA. 273(14):1118-22.

Voetsch AC, Angulo FJ, Jones TF, Moore MR, Nadon C, McCarthy P, Shiferaw B, Megginson MB, Hurd S, Anderson BJ, Cronquist A, Vugia DJ, Medus C, Segler S, Graves LM, Hoekstra RM, Griffin PM; Centers for Disease Control and Prevention Emerging Infections Program Foodborne Diseases Active Surveillance Network Working Group (2007). Reduction in the incidence of invasive listeriosis in foodborne diseases active surveillance network sites, 1996-2003. Clin Infect Dis. 15;44(4):513-20.

Weinberg, WG. (1996). No Germs Allowed: How to Avoid Infectious Diseases At Home and On the Road. Piscataway, NJ: Rutgers University Press.

  • John Munsell

    What is/are the most likely source (origin) of listeria? It is frequently stated that if we traceback E.coli & Salmonella as far as possible, that we will eventually bump into a cow, which is the source. The article above makes references to livestock (unpasteurized milk), thoroughly cook raw food from animal sources, avoiding soft cheeses, etc. So, are animals the source of listeria, or is listeria environmental bacteria, ubiquitous throughout our environment?
    Thanks in advance for your answers.
    John Munsell

  • Minkpuppy

    If I remember my microbiology correctly, Listeria is one of those bugs that’s just about everywhere and can live in the soil, just like Salmonella and a number of other bacteria that are of animal/ human health concern.
    Listeria loves cool, moist places so that’s why it’s a bugger in processing plants. It hides out in drains and coolers in the condensate. Condensation over food/meat products is really becoming a major issue during inspections because of Listeria.

  • Sam

    John,
    Listeria is ubiquitous; it can be found globally in soils.