Doctors and epidemiologists often overlook Listeria, another food-borne bacterium, as a cause of food-borne illness. This is because the bacterium is difficult to grow in the laboratory, and it is often confused with harmless contaminants that can grow in a culture and therefore are disregarded. Listeria can survive at low temperatures. In other words, it can be transmitted in ready-to-eat foods even if they have been properly refrigerated.
Listeria live everywhere in the environment. They are in grazing areas, stale water supplies, and poorly prepared animal feed. They also live in the intestines of people, animals, and birds without causing disease. They've been found in cattle, sheep, fowl, dairy products, fruits, and vegetables.
There are 2,500 cases of Listeria in the United States each year, which result in 500 deaths.
Listeria infection is caused by eating contaminated food. The bacterium is often opportunistic, living peacefully in the body until another disease weakens the body's immune system, when it takes advantage of the situation and causes disease. Pregnant women are also more at risk for Listeria infection.
The bacteria travel through the bloodstream and are often found inside of cells. They are able to use the machinery of our cells to avoid our immune system's efforts to fight them. Then they produce toxins, or poisons, that damage our body's cells.
People at highest risk for Listeria infection include the following:
The incubation period for a Listeria infection is one to eight weeks. Most people start to see symptoms a month after initial infection.
Symptoms include fever, muscle aches, nausea, and diarrhea. If the organisms get into the nervous system, symptoms include headache, stiff neck, loss of balance, confusion, and convulsions. If the organisms get into the brain, symptoms mimic those of a stroke.
For pregnant women, the infection often seems mild, with flu-like symptoms. However, it can lead to miscarriages, infection of the newborn, or stillbirths.
Listeria is treatable with antibiotics.
Those at risk for Listeria should avoid soft cheeses, cook leftovers or ready-to-eat foods until they are very hot, fully cook chicken, and avoid uncooked fish, like sushi.
The safe handling of food and proper handwashing and surface cleaning, as reviewed earlier in this section, is also very important.