Listeria is a family of bacteria that contains ten species. One of these, Listeria monocytogenes, causes the disease listeriosis in humans and animals.
Although listeriosis is rare, the disease is often severe with high hospitalisation and mortality rates. In the EU about 1,470 human cases were reported in 2011, with a mortality rate of 12.7%.
Listeria is found in soil, plants and water. Animals, including cattle, sheep and goats, can also carry the bacteria.
Consumption of contaminated food or feed is the main route of transmission to humans and animals. Infections can also occur through contact with infected animals or people.
Cooking at temperatures higher than 65 °C kills the bacteria. However, Listeria can contaminate foods after production (for example contamination can occur after the food is cooked but before is packaged). Unlike many other foodborne bacteria, Listeria tolerates salty environments and can even multiply at cold temperatures (between +2°C and 4 °C).
The hardiness of this bacteria, coupled with the high mortality rates in humans, makes safe food handling paramount to ensure public health.
In infected people, symptoms vary, ranging from mild flu-like symptoms, such as nausea, vomiting and diarrhea to more serious infections such as meningitis and other potentially life-threatening complications. People who are more susceptible to Listeria infections are the elderly, pregnant women, newborn infants and people with weak immune systems.
In domestic animals such as sheep and goats, listeriosis can cause encephalitis, abortion or mastitis. However, animals can also carry the bacteria without becoming ill.
Listeria monocytogenes can be found in many foods. Examples include smoked fish; meats; cheeses (especially soft cheeses) and raw vegetables.
To prevent listeriosis, it is important to follow good manufacturing practices, hygiene practices and effective temperature control throughout the food production, distribution and storage chain including in the home. In the home consumers are advised to keep the temperature of their refrigerators low in order to limit potential growth of bacteria such as Listeria should it be present in ready-to-eat foods. International organisations such as the World Health Organisation advise to refrigerate foods at temperatures below 5 °C.