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Listeriosis is caused by eating food contaminated with a bacterium called Listeria monocytogenes. It’s an uncommon illness but can be deadly if it causes septicaemia (blood poisoning) or meningitis (inflammation of the membranes around the brain).
The elderly are particularly susceptible to listeriosis, as are pregnant women and their foetuses, and those with weakened immune systems such as those on cancer treatment or medications that suppress the immune system. Symptoms include fever, muscle aches and gastrointestinal problems such as nausea, vomiting and diarrhoea.
Infection during pregnancy may lead to miscarriage, stillbirth and newborn infections but the early use of antibiotics can often prevent infection of the foetus or newborn.
Past outbreaks have been linked with raw milk, soft cheeses, salads, unwashed raw vegetables, cold diced chicken, pre-cut fruit and fruit salad.
Listeria is found widely in soil, water and vegetation, and can be carried by pets and wild animals. A vegetable or fruit food product can become contaminated anywhere along the chain of food production: planting, harvesting, packing, distribution, preparation and serving.
Even on a farm, sources of contamination can include irrigated waters, wash waters and soil. Listeria can survive for up to 84 days in some soils. Heavy rains on a crop can splash listeria from soils onto the surface or skin of the vegetable or fruit, especially those that grow low to the ground, such as rockmelons. Their unique, rough skin can also trap and hold bacteria. Melons may be turned multiple times during their maturation to develop properly, which can mean more opportunities to spread pathogens.