Listeria and Escherichia coli

Overview

Why Listeria grows in the fridge, high-risk foods and groups, listeriosis in pregnancy, Escherichia coli O157, haemolytic uraemic syndrome and the 2005 South Wales outbreak.

What you need to know

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Questions from this subtopic

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1. 1

   Why is Listeria monocytogenes unusual among food-poisoning bacteria?

   Model answer

   Listeria monocytogenes can grow slowly at refrigeration temperatures. Chilling alone therefore does not stop it multiplying in ready-to-eat foods.

2. 2

   Which foods are most often linked to listeriosis?

   Model answer

   Chilled ready-to-eat foods such as pâté, soft mould-ripened cheese, smoked fish and cooked sliced meats are the main sources. Pre-packed sandwiches and salads have also caused outbreaks.

3. 3

   Which groups are most at risk from listeriosis?

   Model answer

   Pregnant women, unborn and newborn babies, people over 65 and people with weakened immune systems are most at risk. Healthy adults usually have mild symptoms or none.

4. 4

   Why is listeriosis particularly serious in pregnancy?

   Model answer

   Listeria can cross the placenta and infect the baby. Infection can cause miscarriage, stillbirth or severe illness in the newborn, even when the mother feels only mildly ill.

5. 5

   What are the possible effects of invasive listeriosis?

   Model answer

   Invasive listeriosis can cause septicaemia and meningitis. The death rate is high compared with most other food-borne infections.

6. 6

   Why can listeriosis be hard to link to a particular food?

   Model answer

   The incubation period can be long, sometimes several weeks. People may not remember what they ate, so the source is difficult to trace.

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