Listeria infection - including symptoms, treatment and prevention

Bacterial infection caused by Listeria monocytogenes is called listeriosis.

Listeria infection is a notifiable condition1

How Listeria is spread

These bacteria are widespread in nature, being found in soil, decaying vegetation and the bowels of many mammals.

Listeria infection is mainly spread by eating contaminated foods. Unlike most bacteria, Listeria can multiply in refrigerated foods, if they have been contaminated. Contact with infected farm animals, particularly stillborn animals, can also spread the infection.

Foods at higher risk

Foods associated with the spread of Listeria include:

  • unpackaged ready-to-eat cold meats and packaged sliced ready-to-eat cold meats. For example from delicatessen counters, sandwich bars or supermarkets
  • cold cooked ready-to-eat chicken purchased whole, in portions or diced
  • refrigerated pâté or meat spreads
  • pre-prepared or pre-packaged fruit or vegetable salads, for example salad bars or smorgasbords
  • chilled seafood, including:
    • raw seafood, for example oysters, sashimi or sushi
    • smoked ready-to-eat seafood
    • cooked peeled prawns, for example prawn cocktails, sandwich fillings and prawn salads
  • soft, semi-soft and surface ripened cheeses, either pre-packaged or from the delicatessen. For example, brie, camembert, ricotta, feta and blue
  • soft serve ice cream
  • other unpasteurised dairy products (for example raw goat’s milk).

Signs and symptoms of Listeria infection

People are probably frequently exposed to Listeria, with only mild illness resulting. However, infection is more serious when it occurs in newborn babies, the elderly, immune suppressed people and pregnant women.

Symptoms may include:

  • sudden onset of fever
  • headache
  • backache
  • nausea, vomiting
  • neck stiffness
  • gradual onset of confusion, decreased alertness.

Pregnant women may have relatively mild symptoms (fever and aches) and make a quick recovery. However, they may transfer the infection to their unborn child who may be stillborn or born very ill.

Diagnosis of Listeria infection

The diagnosis is made by growing the bacteria from a sample of cerebrospinal fluid (cerebrospinal fluid: the fluid surrounding the brain and spinal cord), blood or from samples taken from the baby.

Incubation period

(time between becoming infected and developing symptoms)

Varies from 3 to 70 days. The average is 3 weeks.

Infectious period

(time during which an infected person can infect others)

Except for transmission from a pregnant woman to her fetus, person-to-person spread does not occur.

Treatment for Listeria infection

Antibiotic treatment and hospital admission may be required.

Prevention of Listeria infection

Exclusion from childcare, preschool, school and work is not necessary.

Pregnant women and immune suppressed people

Pregnant women and immune suppressed people should take special care to avoid foods which may be contaminated with Listeria. They should follow these guidelines:

  • eat freshly cooked or freshly prepared foods
  • eat well washed, freshly prepared fruit and vegetables
  • cook foods thoroughly, especially meats
  • reheat foods to ‘steaming’ hot
  • make safer food choices and avoid higher risk foods
  • avoid ready-to-eat food from salad bars, sandwich bars, delicatessens and smorgasbords
  • avoid foods that are past their 'best before' or 'use by' date
  • only buy ready-to-eat hot food if it is steaming hot
  • if eating out, order hot meals
  • after handling uncooked food, wash hands, knives and cutting boards with detergent and hot water
  • avoid the use of untreated manure on vegetable crops which will be eaten raw
  • avoid contact with sick or stillborn farm animals.

Useful links

1 – In South Australia the law requires doctors and laboratories to report some infections or diseases to SA Health. These infections or diseases are commonly referred to as 'notifiable conditions'.