Listeria (Listeriosis)

Sources

How does someone get listeriosis?

People get listeriosis by eating food contaminated with Listeria monocytogenes ¹. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy. However, healthy people may consume contaminated foods without becoming ill. People at risk can prevent listeriosis by avoiding certain higher-risk foods and by handling and storing food properly.

Reservoir

Listeria monocytogenes is commonly found in soil and water. Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin, such as meats and dairy products.

Transmission

Vital Signs Graphic: Listeria hides in many foods

Most human infections follow consumption of contaminated food ². Rare cases of hospital-acquired transmission have been reported in newborns ³.

When Listeria bacteria get into a food processing factory, they can live there for years, sometimes contaminating food products ⁴. The bacterium has been found in a variety of foods, such as:

Uncooked meats and vegetables
Unpasteurized (raw) milk and cheeses as well as other foods made from unpasteurized milk
Cooked or processed foods, including certain soft cheeses, processed (or ready-to-eat) meats, and smoked seafood

Listeria are killed by cooking and pasteurization. However, in some ready-to-eat meats, such as hot dogs and deli meats, contamination may occur after factory cooking but before packaging or even at the deli counter. Also, be aware that Mexican-style cheeses (such as queso fresco) made from pasteurized milk and likely contaminated during cheese-making have caused Listeria infections.

Unlike most bacteria, Listeria can grow and multiply in some foods in the refrigerator.

References

Schlech WF, 3rd, Lavigne PM, Bortolussi RA, Allen AC, Haldane EV, Wort AJ, Hightower AW, Johnson SE, King SH, Nicholls ES, Broome CV. Epidemic listeriosis--evidence for transmission by food. The New England journal of medicine. 1983;308(4):203-6.
Painter J & Slutsker L. Listeriosis in humans. In: E. T. Ryser & E. H. Marth., editor. Listeria, Listeriosis and Food Safety 3rd ed Boca Raton, Florida: Taylor and Francis Group; 2007. p. 85-110.
Schuchat A, Lizano C, Broome CV, Swaminathan B, Kim C, Winn K. Outbreak of neonatal listeriosis associated with mineral oil. Pediatr Infect Dis J. 1991;10(3):183-9.
Tompkin RB. Control of Listeria monocytogenes in the food-processing environment. Journal of food protection. 2002;65(4):709-25.