Food poisoning factsheets Shigella infection

What is Shigellosis an how common is it?

Shigellosis is an infectious disease caused by a group of bacteria (germs) called Shigella. It’s also known as bacillary dysentery.

There are four main types of Shigella germ but Shigella sonnei is by far the commonest cause of this illness in the UK. Most cases of the other types are usually brought in from abroad.

How is Shigellosis caught?

Shigella is not known to be found in animals so it always passes from one infected person to the next, though the route may be indirect. Here are some possible ways in which you can get infected:

  • Shigella germs are present in the stools of infected persons while they are ill and for a week or two afterwards. Most Shigella infections are the result of germs passing from stools or soiled fingers of one person to the mouth of another person. This happens when basic hygiene and hand washing habits are inadequate, such as in young toddlers who are not yet fully toilet trained. Family members and playmates of such children are at high risk of becoming infected.
  • Shigellosis can be acquired from someone who is infected but has no symptoms.
  • Shigellosis may be picked up from eating contaminated food, which may look and smell normal. Food may become contaminated by infected food handlers who do not wash their hands properly after using the toilet. They should report sick and avoid handling food if they are ill but they may not always have symptoms.
  • Vegetables can become contaminated if they are harvested from a field with sewage in it. Flies can breed in infected faeces and contaminate food elsewhere.
  • Shigellosis can also be caught by drinking contaminated water that has sewage running into it, or by swallowing while swimming in contaminated water.

What are the symptoms of Shigellosis?

Diarrhoea is the main symptom and it may contain blood. There is often a temperature as well. Symptoms usually start within a day or two of being exposed to Shigella and they clear up in 5 to 7 days.

In some people, especially young children and the elderly, the diarrhoea can be so severe as to require admission to hospital.

Are there any long term complications of Shigellosis?

Usually there are few complications although infection can sometimes spread to the bloodstream. The nastiest type, called Shigella dysenteriae, which is rare in the U.K. and always caught abroad, can lead to severe symptoms and sometimes death.

How do you know if you have Shigellosis and how is it treated?

Many different kinds of diseases can cause diarrhoea and bloody diarrhoea. To make a diagnosis, a stool specimen must be examined in a laboratory.

Treatment of Shigellosis is with antibiotics but not all cases need them. Overuse of antibiotics leads to germs becoming resistant to them, so treatment is restricted to those cases that need it.

Any child with Shigellosis can be allowed back to school 48 hours after diarrhoea stops if their personal hygiene is good. Younger children should stay off for 3 to 4 days after their diarrhoea stops. It’s not feasible for children to be kept off school until the germ is no longer found in their stools, as it may be present there for 2 to 3 weeks after symptoms stop.

What can I do to prevent Shigellosis and what should I do if I have it?

The essentials, as with so many illnesses that cause diarrhoea, are good personal hygiene and care in food preparation:

  • Wash hands thoroughly in hot soapy water after going to the toilet or after changing children’s nappies or soiled clothes.
  • Wash and disinfect toilet seats, toilet handles and taps.
  • Wash fruit and vegetable produce.
  • Proper cooking of foods. Avoid preparing food if at all possible while you have symptoms and for 48 hours afterwards.
  • If you have the illness and work with children or the elderly, or work in a hospital or a food business, advise your supervisor. Your local Environmental Health Department, who can investigate to try and prevent further cases, may contact you.

If you are travelling to the developing world, remember this advice about food - “Boil it, cook it, peel it or forget it”. It works against all food-borne infections!