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Necrotising Fasciitis related infections

conditions related to necrotising fasciitis

Group A streptococcal

What is Group A streptococcal?

A bacterium which looks like small round beads under the microscope and which produces an armamentarium of toxins and surface proteins which combat the human immune system and also cause disease. It is also known as Streptococcus pyogenes, S. pyogenes, or simply “group A strep”.

Where does Group A Strep normally live?

Group A strep normally cause infection in people’s throats and can spread in the community from person to person. 1 – 2% of people may ‘carry’ the bug without knowing and without suffering any illness. Group A strep spreads very easily in conditions where people are housed together in close quarters.

Group A strep also can live on the skin, particularly where the skin is damaged by conditions such as eczema, as well as on any other mucous surface of the body. It cannot survive for very long away from the human body.

What infections can it cause?

Surface Infections

  • Not serious in themselves, but infectious to others:
  • Sore throat (pharyngitis) and tonsilitus
  • Impetigo

Complications of surface infections

  • Quinsy or ear infection
  • Scarlet fever
  • Rheumatic fever
  • Sydenhams Chorea
  • Post-strep reactive arthritis
  • Post-strep glomerulonephritis (kidney inflammation)

Deeper infections (Invasive infections)

As well as causing Necrotising fasciitis Strep A can cause a raft of other conditions.

Cellulitis and erysipelas:

If the bacteria settle in the layers just under the skin surface, the skin will appear reddened and swollen and fever may ensue. This is known as “cellulitis”; a special type of infection is sometimes seen on the face, known as “erysipelas”. The group A streps will continue to grow (by dividing) unless they are killed by the body’s own immune defences or by antibiotics. The skin and tissues under the skin are arranged in layers; the rapidly dividing streptococci simply spread along these layers, resulting in the redness spreading up and down.

This type of infection must be treated with antibiotics; some doctors will try tablet antibiotics first, but usually if there is fever or other signs of severe illness, it is sensible to give antibiotics in the form where they can act quickly, that is, intravenously, which normally requires hospital. It is very difficult to grow bacteria from cases of cellultis, so often the exact bug is not identified. The group A strep is believed to be the commonest cause of cellulitis (except where there had been a boil or insect bite recently). Other bacteria can cause cellulitis, and antibiotics will be tailored to fit the likely infections in any given patient. Sometimes, cellulitis in the leg can mimic a deep vein thrombosis (blocked vein), so doctors may perform scans to check for that.

Once antibiotics are started, doctors will look for signs of improvement (reduction in size of the red area, reduction in fever or pain, improvement in blood tests). If any of these worsen, or if the skin begins to blacken or blister on treatment, the doctors may increase the antibiotic treatment and consider whether the infection could have spread to deeper tissues, or whether there are dead tissues which need to be removed, and whether the antibiotics are targeted at the correct bugs.

Sometimes surgery is needed to explore these possibilities; tissue taken by the surgeons can be tested in the labs for bacteria, and can be examined for evidence of dead tissue. Any dead tissue (‘necrotic”) must be removed surgically, otherwise it will continue to generate a destructive inflammatory response in the body and proved a good ‘culture medium’ for the bacteria to thrive in. Cellulitis can occasionally be complicated by bacteremia (bacteria spreading into the bloodstream) and septic or toxic shock.

Cellulitis and erysipelas:

If the bacteria settle in the layers just under the skin surface, the skin will appear reddened and swollen and fever may ensue. This is known as “cellulitis”; a special type of infection is sometimes seen on the face, known as “erysipelas”. The group A streps will continue to grow (by dividing) unless they are killed by the body’s own immune defences or by antibiotics. The skin and tissues under the skin are arranged in layers; the rapidly dividing streptococci simply spread along these layers, resulting in the redness spreading up and down.

This type of infection must be treated with antibiotics; some doctors will try tablet antibiotics first, but usually if there is fever or other signs of severe illness, it is sensible to give antibiotics in the form where they can act quickly, that is, intravenously, which normally requires hospital. It is very difficult to grow bacteria from cases of cellultis, so often the exact bug is not identified. The group A strep is believed to be the commonest cause of cellulitis (except where there had been a boil or insect bite recently). Other bacteria can cause cellulitis, and antibiotics will be tailored to fit the likely infections in any given patient. Sometimes, cellulitis in the leg can mimic a deep vein thrombosis (blocked vein), so doctors may perform scans to check for that.

Once antibiotics are started, doctors will look for signs of improvement (reduction in size of the red area, reduction in fever or pain, improvement in blood tests). If any of these worsen, or if the skin begins to blacken or blister on treatment, the doctors may increase the antibiotic treatment and consider whether the infection could have spread to deeper tissues, or whether there are dead tissues which need to be removed, and whether the antibiotics are targeted at the correct bugs.

Sometimes surgery is needed to explore these possibilities; tissue taken by the surgeons can be tested in the labs for bacteria, and can be examined for evidence of dead tissue. Any dead tissue (‘necrotic”) must be removed surgically, otherwise it will continue to generate a destructive inflammatory response in the body and proved a good ‘culture medium’ for the bacteria to thrive in. Cellulitis can occasionally be complicated by bacteremia (bacteria spreading into the bloodstream) and septic or toxic shock.

Myositis

Occasionally, bacteria spread from the fascia to the muscle bundles themselves. The symptoms are very similar to necrotising fasciitits, and the treatment also involves surgery to remove any dead muscle plus antibiotics. Doctors can sometimes detect myositis (inflammation of the muscles) using blood tests, even if there is no obvious evidence at surgery. Myositis due to group A strep is often complicated by bacteremia (bacteria spreading into the bloodstream) and septic or toxic shock.

Pneumonia

Group A strep can cause infection of the lung tissue; whether the bug reaches the lung directly from the throat, or whether it reaches the lung via the bloodstream is unknown (and may vary from case to case). Pneumonia due to group A strep was thought to be uncommon but cases are being described more commonly now. It can be a devastating infection, and, like necrotising fasciitis, can be associated with bacteremia (bacteria spreading into the bloodstream) and septic or toxic shock.

Puerperal sepsis (infection around time of childbirth)

Group A strep used to commonly cause severe infections in women around the time of childbirth (“puerperium”). This is much less common nowadays, but, for reasons not completely understood, the weeks around childbirth still represent a risk period for group A strep infections. Group A strep, most commonly spread from infected sore throats, gain access to the pregnant (or recently pregnant) womb, probably via the genital tract. This can result in infection of the membranes covering the fetus (amnionitis, which may result in premature labour or even stillbirth) and/or infection of the lining of the womb (endometritis).

Either condition will cause illness in the mother, and bacteremia (bacteria spreading into the bloodstream) with septic or toxic shock can ensue. Group A Strep infection is considered a very serious infection in such women.

N.B. Group B strep infection is a different type of streptococcal infection, which is important in pregnancy because it can rarely result in devastating infection of the newborn. The group B strep is carried in the genital tract of some pregnant women, and babies acquire the infection at the time of birth.

Bacteremia (bacteria in the blood)

The appearance of bacteria in the blood stream is a serious indicator of deep-seated group A streptococcal infection. Bacteremia is more commonly known as “blood poisoning” and of course can be used to describe the appearance of any bug in the bloodstream. Doctors have to take special blood samples (blood cultures) to detect bacteria in the blood; because the bacteria have to grow in the lab in order to be detected and identified, doctors often do not know the result for a day or two.

Sometimes, doctors may guess that the group A strep is a likely cause of an illness, for example, in necrotising fasciitis, and antibiotics and surgery are planned accordingly. Often, however, the first indication that an infection is caused by group A strep in will be, that the blood culture shows a group A strep. Doctors may have started antibiotics using a ‘best guess’ approach. Fortunately, group A strep is killed by most of the antibiotics commonly used in a wide range of conditions.

It is widely believed that group A strep bacteremia can itself cause a focus of infection in the body by “seeding” abnormal areas, such as a bruised muscle, or faulty heart valve. Seeding appears to be the way in which cases of meningitis arise, although these conditions are exceedingly rare.

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Complications of deeper infections:

Necrotising Fasciitis is a condition related to the infection, not the infection itself. Other complications related to infection include:

R

Septic Shock

R

Toxic Shock

Risk of serious disease

Very rarely, streptococci acquired on the skin can go on to cause more serious disease. Once on the skin, group A streps can enter the deeper parts of the body, by “by-passing” the body’s normal immune defences and by using special ‘tools’ to invade through the barriers covering our body, such as the skin. They are often helped by co-existing conditions which might cause skin breaks, such as chicken pox, or a surgical wound, or even a tiny crack between the toes, such as those sometimes seen with athletes foot.

Wherever the bacteria settle, there will be local inflammation. The body will recognise the bacteria as a danger, and the immune system will send in white blood cells to fight the infection, leading to inflammation. It is the inflammation that alerts us to the presence of an infection.

Who is at risk of invasive group A strep infections?

Although there are recognised groups of people at risk from invasive group A strep infection (skin conditions which allow bacteria in, or medical illnesses which put them at greater risk), almost one third have no risk factors whatsoever.

Predisposing skin conditions.

  • Surgery/recent injury
  • Injecting drug use
  • Chicken pox

Predisposing Medical conditions.

  • Heart disease
  • Diabetes
  • Alcoholism
  • Cancer
  • Lung disease
  • HIV infection
  • Pregnancy
  • No risk factors (30%)

Guidelines for prevention and control

Group A streptococcal infection in acute healthcare and maternity settings in the UK

Hospital outbreaks of group A streptococcal (GAS) infection can be devastating and occasionally result in the death of previously well patients. Approximately one in ten cases of severe GAS infection is healthcare-associated. This guidance, produced by a multidisciplinary working group, provides an evidence-based systematic approach to the investigation of single cases or outbreaks of healthcare-associated GAS infection in acute care or maternity settings.

The guideline recommends that all cases of GAS infection potentially acquired in hospital or through contact with healthcare or maternity services should be investigated. Healthcare workers, the environment, and other patients are possible sources of transmission. Screening of epidemiologically linked healthcare workers should be considered for healthcare-associated cases of GAS infection where no alternative source is readily identified. Communal facilities, such as baths, bidets and showers, should be cleaned and decontaminated between all patients especially on delivery suites, post-natal wards and other high risk areas. Continuous surveillance is required to identify outbreaks which arise over long periods of time. GAS isolates from in-patients, peri-partum patients, neonates, and post-operative wounds should be saved for six months to facilitate outbreak investigation. These guidelines do not cover diagnosis and treatment of GAS infection which should be discussed with an infection specialist.

Crown Copyright © 2011 Published by Elsevier Ltd on behalf of The British Infection Association. All rights reserved.

Read the full guidelines (link dead)

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