Food Focus November 2008
Listeria targets the vulnerable
Listeria bacteria are rife in our surrounding environment. While most people can be exposed to the bacteria with no serious health consequences, the dangerous Listeria monocytogenes strain can cause the disease listeriosis, which can have devastating consequences for vulnerable consumers
Listeria bacteria are found widely in nature and they can be transmitted through food. Although they are sometimes present in unprocessed food, such as raw dairy products, meat, poultry and fish, foods more commonly associated with the bacteria are ready-to-eat products, such as deli meats and salads, soft cheeses and foods with a long refrigerated shelf life. These foods are a particular problem because they may have been prepared well in advance of people eating them, leaving plenty of time for any bacteria to multiply.
One of the issues with Listeria bacteria is that they are hardy. They multiply quickly, even at the recommended refrigeration temperature of 2–4°C, and they can survive in semi-dried delicatessen foods such as salami; on frozen goods; in salty products (up to 10% salt); and in foods packaged in modified atmosphere or vacuum packaging.
Listeriosis is rare but severe
Although listeriosis is uncommon, it can be very dangerous. People more at risk of developing the invasive infection include pregnant women and their unborn children, newborn babies, older people, anyone whose immune system has been weakened by disease or illness, and anyone on medication that suppresses the immune system.
Symptoms usually appear within two to 30 days of eating contaminated food, but sometimes it takes up to 70 days before people get sick. Common symptoms include aches and pains, fever, headache and tiredness. Less commonly people suffer from diarrhoea, nausea and abdominal cramps. The illness may progress to more serious forms, such as meningitis and blood poisoning.
Every year about 20 to 25 people fall ill with the invasive form of the disease and about a quarter of those die from it. The consequences of getting listeriosis can be severe for pregnant women, as it can lead to miscarriage, premature birth or, in rare cases, stillbirth. The number of recorded listeriosis cases in New Zealand is similar to those of countries we normally compare ourselves with.
In a recent outbreak in Canada, at least 10 people in the vulnerable group died after eating deli meat products contaminated with Listeria monocytogenes from Canadian company Maple Leaf. A further six deaths have been linked to the company’s goods and dozens of others have fallen ill. In a separate outbreak, at least seven pregnant women in Quebec have acquired Listeria from cheese, leading to premature births and illness in their babies.
Taking precautions to avoid listeriosis
If you or anyone in your household is at a higher risk of getting listeriosis, you can reduce the risk by taking certain precautions. It is advisable that you only eat foods that are freshly prepared and well washed, avoid raw milk products, follow good food hygiene practices such as washing and drying hands, and cook foods thoroughly to kill any Listeria bacteria. In general it is also recommended not to eat soft cheeses and processed meats. Refrigerate leftovers immediately, do not keep them for more than two days in the fridge and reheat them until piping hot (over 70°C) before eating. When eating out, choose food that is steaming hot and freshly prepared.
NZFSA has two free booklets to help consumers choose safer foods and manage the risks associated with Listeria:
• Food safety when you have low immunity.
These resources are available at no charge – call the consumer helpline on 0800 693 721 (0800 NZFSA1) or email info@nzfsa.govt.nz to order them.