What is Listeriosis
Listeriosis, is a rare but serious disease caused by the bacteria Listeria monocytogenes [L. monocytogenes] that can survive and grow on certain high risk foods. While it is probably common for people to eat foods contaminated with a small amount of the bacteria, only some people are at risk of becoming sick. The people who do get sick may require hospitalisation and it may lead to death.
What are the symptoms?
Listeriosis can cause different symptoms depending on which part of the body has been affected and the usual health of the person. Symptoms can include fever, muscle aches, and sometimes nausea and diarrhoea. Infection with L. monocytogenes may also cause septicaemia [blood poisoning] and meningitis [inflammation of the outside of the brain], and death can occur because of these complications.
Pregnant women generally experience mild symptoms themselves; however infections during the pregnancy can lead to miscarriage, stillbirth or infection of the newborn baby.
Symptoms usually start between 3 to 70 days [average 21 days] after eating food contaminated with the bacteria.
How is it spread?
L. monocytogenes is commonly found in the environment [such as soil] and some raw foods. Unlike many other bacteria, L. monocytogenes are unusual because they can grow in the refrigerator. Eating foods that contain L. monocytogenes does not cause illness in most people however some can become sick.�Babies can be born with listeriosis if their mothers eat contaminated food during the pregnancy.
Listeriosis does not spread from person-to-person.
Who is at risk?
Eating foods that contain L. monocytogenes does not cause illness in most people. The disease mainly affects the elderly, pregnant women and their unborn and newborn babies, and people with weakened immune systems due to illness or medication [for example, people on cancer treatment or steroids, and people with diabetes, kidney disease, liver disease and HIV infection].
How is it prevented?
If you [or someone in your household] have a weakened immune system or are pregnant, the best way to avoid L. monocytogenes is to eat freshly cooked or freshly prepared food.
Try to avoid foods that have a higher risk of L. monocytogenes contamination such as:
- chilled seafood such as raw oysters, sashimi and sushi, smoked ready-to-eat seafood and cooked ready-to-eat prawns
- cold meats from delicatessen counters and sandwich bars, and packaged, sliced ready-to-eat meats
- cold cooked ready-to-eat chicken [whole, portions, or diced]
- rockmelon
- pre-prepared or pre-packaged fruit or vegetable salads, including those from buffets and salad bars
- soft, semi-soft and surface-ripened cheeses such as brie, camembert, ricotta, blue and feta
- refrigerated pat� or meat spreads
- soft serve ice cream
- unpasteurised dairy products
- raw mushrooms.
You can further reduce your risk by:
- avoiding food that is past its best before or use by date
- refrigerating leftovers promptly and using them within 24 hours, or freezing them
- cooking food thoroughly
- reheating food until it is steaming hot.
The NSW Food Authority provides further information on foods to eat and avoid during pregnancy.
How is it diagnosed?
The diagnosis of listeriosis can be confirmed by blood or other tests requested by a doctor.
How is it treated?
Treatment for listeriosis involves antibiotics and supportive care. When infection occurs during pregnancy, antibiotics can often prevent infection of the unborn baby or newborn.
Listeria in Australia
While listeriosis can be a very severe illness, the number of cases reported in Australia each year is relatively low, with around 80 cases reported each year. Most people infected with listeriosis are not connected to an outbreak, however outbreaks can occur. Outbreaks caused by listeriosis have been associated with rockmelon, delicatessen meats, raw milk, soft cheeses, pre-prepared salads [for example, from salad bars], unwashed raw vegetables, pat�, cold diced chicken and pre-cut fruit and fruit salad.
Preventing the spread of listeria in Australia
Listeriosis is mainly acquired by eating contaminated foods. Food safety standards in Australia are designed to minimise the contamination of food with bacteria including L. monocytogenes. �It is difficult to completely remove the risk as this bacteria is so widespread in the environment. Cases of listeriosis are reported to public health authorities so outbreaks can be identified and managed, and particular causes detected.
Further Information
Talk to your doctor about preventing listeriosis if you are pregnant or if you think you might be at increased risk due to illness or medications.
More information on listeriosis can also be found by contacting your state or territory health department.
Listeria bacteria are found widely in the environment in soil, including in decaying vegetation and water, and may be part of the fecal flora of a large number of mammals, including healthy human adults.
According to the United States Food and Drug Administration [FDA], some healthy adults may be asymptomatic intestinal carriers of the bacteria. Another authority notes that the “organism has been isolated from the stool of approximately 5% of healthy adults.”
According to the Centers for Disease Control and Prevention’s [CDC] National Center for Zoonotic, Vector-Borne, and Enteric Diseases, listeriosis was added to the list of nationally notifiable diseases in 2001:
To improve surveillance, the Council of State and Territorial Epidemiologists has recommended that all L. monocytogenes isolates be forwarded to state public health laboratories for subtyping through the National Molecular Subtyping Network for Foodborne Disease Surveillance [PulseNet]. All states have regulations requiring health care providers to report listeriosis cases, and public health officials should try to interview all persons with listeriosis promptly using a standard questionnaire about high risk foods. To reach this goal, FoodNet conducts active laboratory- and population-based surveillance.
The following table shows selected data from the CDC’s Annual Surveillance Summaries of reported Listeria cases. Increases over time could be explained in part by increased surveillance and reporting.
Table 1. Selected data from the CDC’s Annual Surveillance Summaries of reported Listeria cases
Despite these numbers, CDC’s Technical Information website estimates that there were more than 1,600 cases of Listeria infection annually in the United States based on data through 2008. Although the nature and degree of underreporting is subject to dispute, all sources agree that the confirmed cases represent just the tip of the iceberg.
The Listeria Initiative and PulseNet conduct nationwide surveillance to rapidly detect and respond to outbreaks; the Foodborne Diseases Active Surveillance Network [FoodNet] conducts active, sentinel population-based surveillance to track incidence trends; and the Foodborne Disease Outbreak Surveillance System [FDOSS] receives reports of investigated outbreaks to track foods and settings associated with outbreaks. In a CDC report summarizing data on 2009-2011 listeriosis cases and outbreaks reported to U.S. surveillance systems:
Nationwide, 1,651 cases of listeriosis occurring during 2009–2011 were reported. The case-fatality rate was 21%. Most cases occurred among adults aged ≥65 years [950 [58%]], and 14% [227] were pregnancy-associated. At least 74% of nonpregnant patients aged