Listeriosis is an infection caused by a gram-positive motile bacterium named Listeria monocytogenes. The infection produces fever, muscle aches, and, in many people, diarrhea. Severe infections can cause headaches, meningitis, convulsions, and death. Most healthy people exposed to the bacteria have minor or no symptoms, but a few people, especially the elderly, pregnant females and their fetus, newborns, and anyone with a compromised immune system are especially susceptible to these organisms. Listeria bacteria are widespread throughout the world and are often associated with farm animals that may show no signs of infection. Research shows that many animals are uninfected carriers, and they suggest that some humans carry these organisms as part of their bowel flora. Except for pregnant females and their fetus or newborn, there is no direct transfer of Listeria from human to human.
The organisms (Listeria monocytogenes) that cause listeriosis have probably been infecting humans for centuries. Listeria was first isolated from an infected WWI soldier in 1918 and had many different names until 1940, when the genus and species names were firmly established. However, the bacteria were first recognized as a food-borne (food poisoning) pathogen in 1979. The bacteria can penetrate human cells and can multiply inside them. People with altered or impaired immune systems have cells that are less able to control the spread of these organisms into the blood or into other cells. In 2010, a known species, Listeria ivanovii, thought only to infect cattle, was found to infect humans.
Listeriosis is mainly a food-borne disease; except in the situation in which a pregnant woman can transfer the bacteria to the fetus or newborn, the disease is not contagious from person to person.
Foods that have been associated with Listeria outbreaks are many (for example, soft cheeses, yogurt, apples, smoked seafood, deli meats, fruits, and vegetables). There have been many outbreaks of the disease over the world; an event occurred in Texas in October 2010, tentatively related to locally processed celery; 10 people were diagnosed with listeriosis and five died. Most people infected had underlying medical problems or conditions. In 2011, approximately 146 people got infected from Listeria-contaminated cantaloupes and about 32 people died. In February 2012, over 1 million eggs were recalled after several processed in a processing plant were found to be contaminated with Listeria. The eggs were sold under the brand names of Columbia Valley Farms, GFS, Glenview Farms, Papetti's, Silverbrook, and Wholesome Farms. The egg brands were sold in 34 states. The year 2015 has already had at least three outbreaks of listeriosis. Bidart Brothers of Bakersfield, Calif., produced apples that eventually were determined to be contaminated with the bacteria. The organisms were first noticed in apples that were caramel coated. Hummus produced by the Sabra Dipping Company was recalled (30,000 cases of hummus) because the food was found to be contaminated with Listeria. Also in 2015, the very popular brand of ice cream, Blue Bell, caused a serious outbreak of listeriosis. To date, three deaths have occurred and the company has shut down at least one of its ice-cream-producing plants in Oklahoma. The recall is ongoing and items produced in the Broken Arrow, Okla., plant that have a code date ending in O, P, Q, R, S, or T are being withdrawn from shelves in a large number of U.S. states. Individuals who have purchased Blue Bell ice cream produced in the Broken Arrow plant with any of these codes should discard the items.