Listeria (Listeria monocytogenes) are bacteria that can cause serious illness and in some cases death, particularly in vulnerable people. In Australia each year around 150 people are hospitalised with listeriosis and about 15 people die.
People at greater risk from listeriosis include pregnant women, their unborn and newborn babies, the elderly and other people whose immune systems have been weakened by illness or drugs (for example: cancer patients, organ transplant recipients, and people on drugs like cortisone).
Eating foods contaminated with Listeria is the most common way of contracting the illness. Listeria is common in the environment and can contaminate different types of food. Listeria is tolerant to low temperatures so it can grow in food even if it is stored in the refrigerator.
More information at the link above.