Listeriosis is a bacterial infection usually caused by eating food contaminated with the bacterium Listeria monocytogenes. It is a relatively rare disease with 0.1 to 10 cases per 1 million people per year depending on the countries and regions of the world.
Listeriosis can happen to anybody who eats contaminated food. You feel sick to your stomach, and you might come down with diarrhea. It usually goes away on its own, but can cause serious problems if you’re pregnant or have a weak immune system.
There are two main types of listeriosis: a non-invasive form and an invasive form.
- Noninvasive listeriosis (febrile listerial gastroenteritis) is a mild form of the disease affecting mainly otherwise healthy people. Symptoms include diarrhoea, fever, headache and myalgia (muscle pain). The incubation period is short (a few days).
- Invasive listeriosis is a more severe form of the disease and affects certain high risk groups of the population. These include pregnant women, patients undergoing treatment for cancer, AIDS and organ transplants, elderly people and infants. This form of disease is characterized by severe symptoms and a high mortality rate (20%–30%). The symptoms include fever, myalgia (muscle pain), septicemia, meningitis. The incubation period is usually one to two weeks but can vary between a few days and up to 90 days.
Listeriosis is caused by bacteria called Listeria monocytogenes that can grow at cold temperatures, like those inside a refrigerator. The disease is usually caught from eating food containing listeria bacteria.
You can get it from lots of food, but it’s mainly a problem with:
- unpasteurised milk
- dairy products made from unpasteurised milk
- soft cheeses, like camembert and brie
- chilled ready-to-eat foods, like prepacked sandwiches, pâté and deli meats
Besides the above mentioned foods, listeriosis can also be gotten from:
- someone else who has it – for example, if you eat food they have handled when they have not washed their hands
- close contact with farm animals – especially sheep and cows that are giving birth.
Listeriosis can cause a variety of symptoms, depending on the person and the part of the body affected.
A person with listeriosis usually has fever and muscle aches, often preceded by diarrhea or other gastrointestinal symptoms. Almost everyone who is diagnosed with listeriosis has invasive infection (meaning that the bacteria spread from their intestines to their blood stream or other body sites). The disease may occur as much as two months after eating contaminated food.
The symptoms vary with the infected person:
- High-risk people other than pregnant women: Symptoms can include fever, muscle aches, headache, stiff neck, confusion, loss of balance, and convulsions.
- Pregnant women: Pregnant women typically experience only a mild, flu-like illness. However, infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.
- Previously healthy people: People who were previously healthy but were exposed to a very large dose of Listeria can develop a non-invasive illness (meaning that the bacteria have not spread into their blood stream or other body sites). Symptoms can include diarrhea and fever.
If the infection spreads to the nervous system, it’s more serious. This happens most often with the very young, the very old, and people with weakened immune systems. The signs could be:
- Stiff neck
- Loss of balance
For minor infections, medication might not be required as it usually goes away on its own. For more serious cases of listeriosis, antibiotics are the most common treatment choice; ampicillin can be used alone or in conjunction with another antibiotic (often gentamicin).
If septicemia or meningitis occur, the individual will be given intravenous antibiotics and require up to 6 weeks of care and treatment.
- Raw vegetables contaminated by soil or by manure that was used as fertilizer
- Animal meat that is contaminated with listeria
- Milk that wasn’t pasteurized, and other products made from it
- Processed foods such as deli meats and hot dogs that are contaminated after they’re produced
How to Protect Yourself
Be sure to wash your hands. Clean them well with warm, soapy water before you start cooking. If you handle raw meat or poultry, wash them afterward.
Here are some other good ideas for cleaning, handling, and cooking food:
- Clean all kitchen surfaces, cutting boards, and utensils with hot, soapy water when you finish cooking.
- Scrub raw vegetables with a brush under running water and ensure you wash your hands with soap before handling them.
- Cook meat, poultry, and egg dishes until they reach 160 F in the center. Use a meat thermometer to make sure. Keep uncooked meat and poultry away from other food.
- Use hot dogs within a week after you open the package, and deli and luncheon meats within 3 to 5 days after opening.
- Keep the temperature below 40 F in the refrigerator, and below 0 F in the freezer.