Listeriosis is caused by the Listeria monocytogenes bacteria, commonly called listeria. It is found in soil and water and is the cause of a small but severe number of cases of illness in New Zealand.
The disease primarily affects older adults, pregnant women, newborns, and adults with weakened immune systems. People without these risk factors can also be affected, although it is rare.
About 90% of cases of listeriosis are due to the consumption of foods or beverages contaminated with high levels of the listeria bacteria.
Sources of contamination
Listeria monocytogenes is found in soil and water. Animals can carry the bacteria without appearing ill and can contaminate foods of animal origin, such as meats and dairy products. Listeria is unusual because it can grow at low temperatures, including refrigeration temperatures below 5ºC.
When listeria get into a food operation, they can live for years, sometimes contaminating food products. The bacteria can be found in a variety of raw, cooked, and processed foods.
It occurs in raw foods such as:
- uncooked meats
- unpasteurised milk
- fruit and vegetables.
It also occurs in ready-to-eat foods that become contaminated after cooking or processing, such as:
- soft cheeses made with pasteurised and unpasteurised milk
- processed meat and poultry – especially those in factory-sealed packages and products sold at deli counters, such as pâtés and ready-cooked meals
- smoked seafood – especially smoked fish
- fresh-cut plant products – such as fruit and vegetable salads.
Symptoms and effects
Listeriosis is a rare but potentially life-threatening disease. Although less common than campylobacteriosis and salmonellosis, listeriosis has a high death rate, particularly among vulnerable groups.
Healthy adults are likely to experience only mild infection, causing flu-like symptoms or gastroenteritis. However, listeria infection can occasionally lead to severe blood poisoning (septicaemia) or meningitis.
The people most susceptible to listeria are:
- pregnant women
- newborn babies
- elderly people
- people with weakened immune systems.
Listeria infection is particularly dangerous in pregnancy. While symptoms are usually mild, it can cause miscarriage, premature birth, or severe illness in a newborn child. In rare cases, stillbirth may occur.
MPI's listeria risk management strategy aims to contain listeriosis levels by working with industry to develop appropriate control measures.
Read the 2008–2013 strategy document: