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Necrotising fasciitis

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Necrotising fasciitis is an infection which destroys areas of the skin and the tissues underneath. It is a very severe condition which can be fatal. Necrotising fasciitis can be treated successfully if diagnosed quickly.

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What is necrotising fasciitis?

Necrotising fasciitis is a rare but very serious infection of the skin and underlying tissues. It is pronounced neck-roe-tie-zing fash-ee-eye-tis. It is sometimes called the flesh-eating bug, or flesh-eating disease.

It can start anywhere in the body, but most commonly it starts in feet, the lower legs, hands, or around the genital areas. If it is around the genitals, it may also be called Fournier's gangrene. When it occurs under the tongue, it may be called Ludwig's angina.

What causes necrotising fasciitis?

Necrotising fasciitis is caused by infection with some kind of germ, usually bacteria. The germs spread from just under the skin to the tissue beneath it, causing a destruction of these tissues. There may be more than one type of germ causing the infection.

There are four different types, depending on the type of germ involved.

  • Type 1: several types of germ are involved.

  • Type 2: caused by a group A streptococcus, sometimes with a staphylococcal infection also.

  • Type 3: caused mainly by a type of bacteria found in seawater environments.

  • Type 4: caused by an infection with a fungus.

The germs multiply and release harmful substances which cause the blood in the small blood vessels to clot, blocking the blood vessels. This leads to the death of the tissues supplied by those blood vessels - usually the soft tissues under the skin and the tissue which covers the muscles (fascia).

The infection starts in a place where the skin has been damaged - for example, due to a surgical operation, a wound from an injury, a bite, or a burn. Sometimes even very minor skin breaks can be the cause - for example, a sting, an injection or an acupuncture needle.

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Who gets necrotising fasciitis?

Usually necrotising fasciitis occurs in people who are more vulnerable due to having another health condition. However, it can occur in people who were entirely healthy. Type 2 infection is the one which is most likely in people who are otherwise healthy.

Conditions or situations which put you at an increased risk of necrotising fasciitis include:

How common is necrotising fasciitis?

It is an uncommon condition. It is estimated to affect about 500 people per year in the UK. It affects men and women equally. It can occur in children but is less common in children than in adults. In children it sometimes starts from a chickenpox spot.

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What are the symptoms of necrotising fasciitis?

Symptoms of necrotising fasciitis usually come on quite quickly after the break in the skin occurred. It then tends to develop very rapidly, over a few days or even less. At first, the affected skin looks slightly reddened and swollen. It is usually extremely painful. The pain is often out of proportion to the minor changes that are seen at first on the skin. It also causes you to feel unwell in yourself, sometimes with a high temperature (fever), flu-like symptoms, or just generally feeling unwell.

As it progresses the affected skin develops blisters and purple, then blackened, areas. The skin feels very tender to touch, even around the area where you can see the skin changes. As the condition progresses further, nerves become destroyed and then the severe pain goes and the area becomes numb. The infection causes you to feel very unwell in yourself, with a fever and thirst due to becoming dehydrated.

Later, the infection can cause symptoms such as diarrhoea, vomiting, dizziness, confusion and collapse. It can go on to cause generalised infection (sepsis) and failure of the vital organs, and sometimes can cause death.

What are the tests for necrotising fasciitis?

Necrotising fasciitis is known to be difficult to diagnose in the early stages. At this point it appears to be similar to other much less severe skin infections, and can be missed until the appearance becomes more severe and more typical. Mostly it is suspected and diagnosed from the typical symptoms and appearance of the skin. It may be possible to feel a crackling under the skin due to gas in the tissues. X-rays or scans may be useful as they may show this gas within the tissues. A test called the 'finger test' may be done - a cut is made into the affected area and gently explored with a gloved finger. If there is necrotising fasciitis, the finger passes straight through destroyed tissue with no feeling of resistance as there would normally be. Blood tests and a biopsy can help in determining the germ or germs causing the infection so that treatment can be targeted accordingly. An operation may be needed to look at the tissues directly to make the definite diagnosis.

What is the treatment for necrotising fasciitis?

A person with necrotising fasciitis would be admitted to hospital urgently, often into intensive care. Treatment is with an operation, with antibiotics and intensive supportive treatment.

  • Surgery. Under general anaesthetic, the affected tissue is removed and the area cleaned. This may be have to be done on a number of occasions, followed by daily dressings. Often large areas of skin have to be treated in this way, which can leave huge gaps in the skin. Strong painkillers (such as opiates) and/or a sedative may be needed while the dressings are done as this can be very painful. Once the infection has been treated, in time the remaining open wounds may need skin grafts to help them close up. Sometimes amputation of an affected limb is needed to stop the spread of infection.

  • Antibiotics. High doses of IV antibiotics are used to try to halt the infection. Usually several antibiotics are given.

  • Supportive treatment. Close monitoring is essential; for example, of fluid levels, for signs of sepsis, for blood pressure and for failure of the vital organs. IV fluids are often required, as there can be a lack of fluid in the body (dehydration). Large areas of damaged skin cause the loss of a lot of fluid and also nutrients such as protein. So extra nutrition is often needed, often via a vein or by a tube going into the stomach through the nose (nasogastric tube). Strong painkillers are likely to be used.

What is the outcome?

If the infection is spotted and treated quickly, the outcome (prognosis) can be excellent and the infection can be cured. Sadly, however, even when the condition has been treated, people can die from necrotising fasciitis. It is estimated that about 2-4 out of every 10 people with the condition do not survive. If the infection occurs in an arm or leg then in nearly a quarter of cases the limb has to be amputated or partially amputated. If the condition is successfully treated, plastic surgery or skin grafts may be needed to repair the skin and tissues left behind, as large gaps may be left behind from removed tissues.

Can necrotising fasciitis be prevented?

Good wound care and hygiene principles can help to prevent this condition. Wounds should be kept clean and dry. All wounds to the skin, even tiny ones, should be cleaned with running water. Dry and cover larger wounds with a sterile dressing. Consider using an antiseptic cream. Wash your hands regularly with soap and water. Avoid swimming pools, hot tubs and open water if you have an open wound.

Currently it is not thought that necrotising fasciitis can be passed from person to person.

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The information on this page is written and peer reviewed by qualified clinicians.

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