About group A streptococcal infections

What is it?

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 it normally live?

Group A strep normally live in people’s throats and can spread in the community from person to person. Often, up to 15% 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
  • Sore throat (pharyngitis)
  • Impetigo

Complications of surface infections

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

Deeper infections

  • Cellulitis and erysipelas
  • Necrotising fasciitis
  • Myositis
  • Pneumonia
  • Puerperal sepsis (infection around time of childbirth)
  • Rarer infections
  • Bacteremia (bacteria in the blood)

Complications of deeper infections

  • Septic Shock
  • Toxic Shock

By Shiranee Sriskandan FRCP. PhD. Imperial College London

Guidelines for prevention and control of 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.

Read the full guideline on the Health Protection Agency website.

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

Necrotising fasciitis

Necrotising fasciitis can be caused by a number of bacteria, but the group A strep is a leading cause in about half of all cases which arise in the community setting.

If group A streptococci spread below the thick layers under the outer skin surface, they will reach the connective tissue or “fascia” These are the fibrous bands of tissue which separate muscle bundles. Arranged in layers, with blood vessels and fats within them, these fascia provide a “freeway’ for group A streptococci to spread. Sometimes, the group A streptococci arrive in the connective tissues via the bloodstream, almost silently. It is believed that these bacteria acquire a more invasive nature, enter the bloodstream perhaps via the throat, and then ‘seed’ previously damaged soft tissues. Some patients have a memory of a seemingly trivial injury that subsequently becomes a focus for infection. The immune response will attempt to contain the infection but, in some cases, the bacteria will succeed in establishing an infection.

As the infection is deep and well below the outer skin, redness and swelling of the skin may not occur (unless there is cellulitis as well). The classical symptom is severe pain, in association with a fever or other ‘flu-like symptoms. Skin changes may begin to occur in the later stages of illness and include blistering and colour change. This is usually a clear sign that tissue in the fascia has died as a result of infection. Antibiotics will normally be administered quickly to assist in killing bacteria, but the main aim of treatment will be to remove as much dead or dying tissue as possible.

This will involve surgery, which may be carried out repeatedly, as surgeons attempt to identify dead areas of tissue and preserve parts which are not dead. Sometimes surgery is quite disfiguring, due to the part of the body involved, or the extent of disease. There is a difficult balance between preserving normal body shape and performing surgery which may be life-saving. Plastic surgery may be required in the convalescent period. Some cases of necrotising fasciitis due to group A strep are complicated by bacteremia (bacteria spreading into the bloodstream) and septic or toxic shock.

Patients who are particularly ill may be nursed in the intensive care unit. Sometimes, patients are given intravenous immunoglobulin (“IVIG”) which is an infusion of antibodies purified from large numbers of blood donations. Antibodies are proteins made by the immune system to fight infection. IVIG might help the body’s immune response to the streptococcal toxins and bacteria, although clinical trials to prove that IVIG provides extra benefit are hard to conduct.

Group A strep tends to affect the arms, legs, or less commonly, the trunk of the body. It is important to recognise that other bacteria can also cause necrotising fasciitis. Roughly half of all cases of NF are due to other bacteria which act as a ‘team’ to cause a similar aggressive infection which results in the death of tissues in the fascia. These cases often follow surgery or injury to the abdominal wall. Diabetics are more prone to the condition.

Bacteria from the bowel or groin area team up with other common skin bugs to invade the tissues of the abdominal wall (sometimes known as “Meleney’s synergistic gangrene”) or in the groin (sometimes known as “Fournier’s Gangrene”). In these cases, the layers of tissue immediately under the skin are often involved as well, and the infection is often more obvious.

Distinguishing a simple post-surgical wound infection from necrotising fasciitis can sometimes be difficult but worsening of symptoms, blood tests, and skin changes provide good evidence. As with group A strep necrotising fasciitis, surgery to remove all dead tissue is essential, along with antibiotics which kill all the likely bacteria.

By Shiranee Sriskandan FRCP. PhD. Imperial College London

Surface infections caused by Group A streptococcus

A proportion of those carrying the bug might develop a sore throat with swollen tonsils. If severe, this might be associated with fever and swollen glands in the neck. This is particularly common amongst children, possibly because they haven’t yet developed immunity to the bug. It is extremely rare for a sore throat infection to progress to anything more serious. Treatment involves detecting the bug (e.g. from a throat swab) and giving antibiotics to cure the infection.

Occasionally, a child may develop a reddish rash during a strep sore throat, which goes pale on pressing; this is known as ‘scarlet fever’ and is quite rare now. Some children and young adults develop recurrent problems with group A strep sore throat, and occasionally some have their tonsils removed to reduce this recurrence. Some children are troubled by group A strep infections around the vulva, vagina, or even the anus.

The child might complain of soreness, itching, and discharge. Provided that a swab is taken for testing, the condition can be easily treated with the correct antibiotics. It is likely that the streps carried in the throat are the source for these types of infections.

Simple ‘surface’ skin infections with group A strep can be troublesome but can be readily dealt with by antibiotic treatment; examples include impetigo. All of these conditions may provide a source of streptococci that can go on to infect others. Repeated or untreated strep infections, in particular sore throat, can be associated with a number of complications caused by our immune responses to the bug. Examples include rheumatic fever (which can affect the heart valves, brain, skin, and joints), post-strep reactive arthritis and glomerulonephritis (kidney inflammation). All of these conditions are unusual in the U.K. but are fairly common in developing countries where strep infections are more common.

Recognised complications following streptococcal surface infections

  • Rheumatic Fever (arthritis, fever, rash, heart valve inflammation)-can lead to chronic heart valve disease especially in developing countries
  • Sydenham’s Chorea (abnormal movement disorder)
  • Post-streptococcal reactive arthritis (PSRA)-arthritis following streptococcal infections; no clear risk of any heart disease
  • Glomerulonephritis (PSGN) Kidney disorder with protein and blood in the urine. Can follow skin infection
  • Guttate psoriasis

Possible complications following streptococcal surface infections.

  • PANDAS (“paediatric autoimmune disorders associated with streptococcal infections”; includes some tic disorders
  • Kawasaki Disease-childhood disease with fever, swollen lymph glands, rash; (can be complicated by swelling of blood vessels around the heart)

By Shiranee Sriskandan FRCP. PhD. Imperial College London

Invasive infections caused by group A strep

Cellulitis and Erysipelas

StrepApiechartIf 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 will perform scans to check for that.

Types of invasive group A strep infection, shown
as proportions of all invasive group A strep infections

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.


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.


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 (childbirth-related) sepsis

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 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.

N.B. Group B strep infection is a different type of streptococcal infection, which is important in pregnancy because it can 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 and Septicemia

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 many cases of meningitis arise.

By Shiranee Sriskandan FRCP. PhD. Imperial College London

Further Information

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 alert 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%)

Streptococcus pyogenes

Strep.pyogenes is a bacterium (germ) which can be found in the throat and sometimes the nose. It can also be carried on the skin. Children are more likely to be carriers than adults. Strep. pyogenes may also be found in the environment where it may persist for weeks in dust and on furnishings.

Strep. pyogenes infections

The common infections caused by Strep. pyogenes are sore throats and skin infections, which are easily treated. Most types of Strep. pyogenes do not cause serious human infections, but a few types have this ability and can cause infections deep within the body including necrotising fasciitis. Many are accompanied by septicaemia (blood poisoning). All are serious, life-threatening and require urgent investigation and treatment. Despite this, the overall death rate is 25-40%.

In most half the cases, the source of the deep infection is never determined. Damage to the skin is the most common source of infection, for example, infection in minor cuts and grazes. Deep infections may also occur after surgery or childbirth. Patients with diseases such as diabetes, in which the blood supply to the tissues is poor, are most susceptible.

Rarer deep infections caused by Strep. pyogenes

Occasionally, the group A strep is found to cause infections like meningitis (infection of the lining of the brain), infection of a joint (septic arthritis), bone (osteomyelitis), abdominal cavity (peritonitis), eye (ophthalmitis), or heart valve (endocarditis). Sometimes, if pus (abscess) or dead tissue has collected, needle aspiration or surgery is needed alongside antibiotics. All of these infections can be associated with bacteremia (bacteria spreading into the bloodstream; “blood poisoning”) and septic or toxic shock.

By Shiranee Sriskandan FRCP. PhD. Imperial College London