Have you ever wondered why doctors tell pregnant women to stay away from pate, deli meats, and brie cheese? Listeria monocytogenes, which can be found in many cold deli foods, is a common infectious microbe that causes listeriosis. In healthy people, listeriosis typically causes a mild stomach infection. But for for people with weakened immune systems, it can cause a serious bloodstream infection, even death. Also, in pregnant women, it can even cross the placenta and cause a slew of problems for the fetus.
Did you know? Unlike most other bacteria, which don’t grow in cold temperatures, Listeria can grow at temperatures below freezing.
Species Name: Listeria monocytogenes
Type of Microbe: Gram-positive bacteria
How it spreads: Food-borne. Listeria is found widely in nature, including in soil and vegetation, and therefore easily contracted by herd animals, including cows, sheep, and chickens. Consumption of contaminated foods, such as poorly washed vegetables, and unpasteurized milk products, results in the disease.
Who’s at risk for invasive disease? Normally listeriosis causes a mild, limited infection in health people. But it can cause serious illness in people whose immune systems are weakened, such as pregnant women, people with AIDS, those who take steroids for inflammation, have cancer, diabetes, or kidney disease, newborns, and the elderly.
More on the Two Forms of Listeriosis
Limited gastroenteritis: Roughly 24 hours after a large exposure to contaminated food, people develop fever, watery diarrhea, nause and vomiting with headache and bodyaches. In people without risk factors (a weak immune system), the disease normally goes away within two days and people recover normally.
Invasive disease: This is rare but more likely to be seen by doctors because of its severity. Bacteria consumed through contaminated food penetrate the intestines and enter the blood stream. This more severe form is more common in pregnant women, those with weak immune systems and older adults. It can cause flu-like symptoms with fever and pain in pregnant women to blood stream infections and septic shock in the elderly, newborns and those with weak immune system. Infection of the central nervous system is possible but rare.
Epidemiology: Approximately 2,500 people are diagnosed with listeriosis in the U.S. every year, of whom 500 people die from the infection. More mild infections are probably not reported and recorded.
Symptoms: Fever, muscle aches, sometimes nausea or diarrhea.
Diagnosis: Blood or spinal fluid test, and rarely it can be detected in the stool
Prognosis: Most healthy adults and children who get infected will not become seriously ill. In healthy adults, listeriosis infections either cause no symptoms or mild flu-like symptoms. In people with weakened immune systems, however, listeriosis is fatal in about one-third of all cases, even with antibiotic treatment. Infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or infection in the newborn.
Treatment: Antibiotics. For people who have the mild form of the disease, confirmation of listeriosis may take 48 hours, and the person may already have recovered, meaning no treatment is needed.
Prevention: Pasteurization of milk and milk products; individuals at risk (pregnant women, infants, and the elderly) should avoid eating raw or undercooked animal products and soft cheeses. Safe food preparation and dining habits should be practiced.
How it causes invasive disease: After eating a contaminated food, Listeria enters the human body through the intestines and hides from the immune system by entering cells, where they can multiply and “borrow” our cellular proteins to help them move within the cell and to other cells. After entering the intestines, it makes its way to the liver, where it multiplies, enters the bloodstream, and invades the brain or uterus, causing an infection in the brain or in the fetus.
Immune response: Listeria causes disease in people who have weakened immune systems. In healthy individuals, infection is controlled by white blood cells, called “T cells” in the “cell-mediated immunity” branch of the immune system.
Complications: Meningitis, septicemia, and perinatal/neonatal infections are all potential complications that have a high risk of death.
Sources:
Listeriosis. Division of Foodborne, Bacterial and Mycotic Diseases. CDC
Listeria monocytogenes. USFDA Bad Bug Book. Center for Food Safety and Nutrition.
Ramaswamy V, et al. Listeria—review of epidemiology and pathogenesis. J Microbiol Immunol Infect. 2007;40:4-13.
