Listeria Monocytogenes


Listeria monocytogenes is a bacterium and is one of the leading causes of death from foodborne illness.

Listeria monocytogenes

Listeria monocytogenes is ubiquitous in the environment. It could be present in a humid or moist environment, decaying vegetation, and soil. This bacterium is very persistent in the food- manufacturing industry, raw materials, and sources of incoming air.  This pathogen causes two forms of illnesses classified according to their severity. The first form can range from mild to intense gastrointestinal illness, and it goes away by itself. The second manifestation is serious and life-threatening. It may cause meningitis or septicemia. Those conditions occur when the infection spreads via the bloodstream to the nervous system. The severe form of this infection has a fatality rate of 15% to 30%. In the case of meningitis, the death rate is as high as 70%. In Toronto, 2008, a listeriosis outbreak in maple leaf plant caused 22 deaths.

Reservoirs & Transmission


Listeria monocytogenes outbreaks and  cases have been traced back to different types of foods; examples are, raw or under‐pasteurized milk; smoked fish, and seafood; meats, including deli meats; cheeses; and raw vegetables. Listeria is hardy; it tolerates salty environments and cold temperatures, unlike many other foodborne bacteria.


Listeria monocytogenes may cause two forms of disease. One could range from mild to intense symptoms of nausea, vomiting, aches, fever, and, sometimes, diarrhea, and usually goes away by itself. The second form is a more deadly form. It  occurs when the infection spreads through the bloodstream to the nervous system (including the brain), resulting in meningitis and other potentially fatal problems.

Susceptible Populations

Pregnant women are more susceptible to Listeria infection than others. Although they recover, their babies usually do not survive.  At-risk also are food workers, pregnant women, immunocompromised people, and the elderly.


Keep Clean: Wash your hands before, during and after handling food. Wash utensils, cutting boards, and any surfaces that food touches after each use. Wash fruits and veggies—but not meat, poultry, or eggs.

Separate Raw and Cooked: Use separate cutting boards, plates, and utensils for raw (uncooked) produce and for raw (uncooked) meat, poultry, seafood, and eggs. Keep meat, poultry, seafood, and eggs separate from all other foods while shopping and in the refrigerator.

Cook Thoroughly and Keep Food at Safe Temperature: Only a food thermometer can make sure meat, poultry, fish, and casseroles are cooked to a safe internal temperature. For example, internal temperatures should be 145°F or 63°C for whole meats (allow the meat to rest after cooking for 3 minutes at least) and fish, 160°F or 71°C for ground meats, and 165°F or 74°C for all poultry. Eggs should be cooked until the yolk is firm.

Chill: Use appliance thermometers to be sure your refrigerator is at or below 40ºF or  4°C and your freezer is 0ºF (-17.78°C) or below. Between 40ºF or 4°C and 140ºF or 60°, C is the Danger Zone, when bacteria can multiply rapidly. Generally, the more bacteria, the more likely someone will get sick. Most refrigerators have just a colder/ warmer adjustment, so the only way to know is to put a thermometer inside.

Hand Washing

  • Before, during, and after preparing food
  • Before eating food
  • Before and after caring for someone at home who is sick with vomiting or diarrhea
  • Before and after treating a cut or wound
  • After using the toilet
  • After blowing your nose, coughing, or sneezing
  • After touching an animal, animal feed, or animal waste
  • After handling pet food or pet treats
  • After touching garbage
  • Use Hand Sanitizer When You Can’t Use Soap and Water. Sanitizers can quickly reduce the number of germs on hands in many situations. Keep in mind, that sanitizers do not kill all types of germs. If your hands are visibly dirty, soap them then use a sanitizer. They also might not remove chemicals, pesticides, and heavy metals from your hands.

The presented information is an extract from the World Health Organization (2008). Foodborne Disease Outbreaks: Guidelines for Investigation and Control. Geneva, Switzerland, 2008