Listeriosis

Listeriosis is an uncommon disease caused by the bacteria Listeria monocytogenes. In the Northern Territory 3 cases of listeriosis have been reported in the past 10 years. Over the same time period there has been an average of 73 cases per year reported throughout Australia.

How it is spread

The disease is generally spread by eating food contaminated with the bacteria, most commonly ready-to-eat meats, and unpasteurised milk or other dairy products particularly soft cheeses.

It can also pass from a pregnant woman to her unborn baby via the placenta, or to the baby during birth.

As the bacteria are widespread in nature and commonly found in soil, water, sewage and most animals, some exposure to these bacteria is generally unavoidable.

Symptoms

Symptoms may develop from a few hours to 3 months after exposure to the bacteria, but most often occur around 3 weeks later. Young, healthy people may have few if any symptoms, but the disease can be severe in at-risk groups.

If symptoms do develop, these often include fever, headache, tiredness, muscle aches, abdominal cramps, nausea and diarrhoea.

If infection spreads to the nervous system, symptoms such as stiff neck, confusion, loss of balance and convulsions may occur.

Who is at risk

The following groups are at greatest risk of severe disease:

• anyone who has a weakened immune system, due to chronic disease, diabetes, alcoholism or steroid treatment
• the elderly
• newborn babies
• pregnant women and their unborn babies.

Although a pregnant woman may have few or no symptoms, the risk of passing the infection on to her unborn baby is high. Infection of the unborn baby usually occurs about 3 days after the mother is infected, and may lead to miscarriage, stillbirth, premature birth or a seriously ill newborn.

Infectious period

Infected people can shed the bacteria in their faeces for several months. Mothers of infected newborns may pass on the bacteria in vaginal discharges and urine for 7 to 10 days after giving birth.

Treatment

Listeriosis can be effectively treated with antibiotics if treatment is given promptly. Newborn infants have a high mortality rate (20-30%) despite antibiotic treatment.

Prevention

Unlike most other food-contaminating bacteria, listeria can survive and grow in the refrigerator, although it is readily killed during cooking.

General food hygiene measures should be followed, including:

• thoroughly cook raw food from animal sources, such as beef, pork or chicken
• wash raw vegetables thoroughly before eating
• keep uncooked meats separate from vegetables, cooked foods and ready-to-eat foods
• avoid unpasteurised milk products
• wash hands, knives and cutting boards after handling uncooked foods.

Additional precautions for pregnant women and those with weakened immune systems include:

• eat only freshly prepared foods
• re-heat left over foods or ready-to-eat foods such as hot dogs until steaming hot
• avoid ready-to-eat foods which have been refrigerated more than a day
• avoid eating dips and salad dressings which have previously been exposed to raw vegetables even if they have been refrigerated
• avoid high risk foods such as pâté, pre-packed sliced meat products, cooked diced chicken (as used in sandwich shops), soft cheeses (such as Brie, Camembert and ricotta), previously prepared coleslaws and salads, uncooked smoked fish, smoked shellfish and any food with an extended shelf life
• avoid contact with animal placenta (afterbirth) and with aborted birth products.

Information for health professionals

To find out more go to the NT Health website.

Contact

For more information call your nearest Centre for Disease Control.