Listeriosis is an infection caused by the bacterium Listeria monocytogenes. Transmission is generally through eating contaminated food, in particular dairy products and ready-to-eat meat and fish products. The bacteria have been found in a variety of raw foods, as well as unpasteurized milk. They are destroyed by cooking, but can grow at refrigeration temperatures. The symptoms of infection include fever, muscle aches, and sometimes nausea or diarrhoea. If infection spreads to the nervous system, headache, stiff neck, confusion, loss of balance and convulsions may occur. In otherwise healthy individuals, infection is usually mild. However, in pregnant women, infection can lead to miscarriage, stillbirth, premature delivery, or infection of the newborn. People with a damaged immune system and the elderly are also at increased risk of more severe disease. The disease has a high fatality rate in the susceptible population.