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Strep A: What is invasive group A streptococcus?

Strep A: What is invasive Group A streptococcus?

Parents have been warned by health officials to be aware of the infections strep A can cause, after the deaths of several children in the UK from it. While most people don't become very ill, the highly contagious bacteria that causes the infection can cause serious illness and can be fatal.

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What is invasive group A streptococcus?

Group A streptococcus (GAS disease), commonly referred to as strep A, is a type of bacteria often found in the throat (strep throat) and on the skin. Group A streptococcal infections commonly cause sore throats, skin infections, or scarlet fever - which causes a skin rash and flu-like symptoms.

In rare circumstances, however, this bacteria can get into the bloodstream, lungs, deep muscles and fat tissue - where it shoudn't be - and cause a serious illness called invasive Group A streptococcus - invasive GAS or iGAS.

Two of the most severe complications caused by iGAS are streptococcal toxic shock syndrome (STSS) and necrotising fasciitis - sometimes called 'flesh-eating' disease.

What are the symptoms of invasive Group A strep?

The early signs and symptoms of invasive disease can include a high fever, severe muscle aches or localised muscle tenderness.

Dr Krishna Vakharia, clinical director of, says the symptoms can vary depending on the affected site - however you will be very unwell. For example, iGAS can cause symptoms of septicaemia, a term used to describe blood poisoning. The symptoms of septicaemia can include a high temperature, clamminess, chills and rapid or shallow breathing - this is a medical emergency - or it can get into the wounds of skin, causing redness and swelling, with fever. Often it is accompanied by diarrhoea and vomiting .

Toxic shock syndrome

Toxic shock syndrome is a rare but life-threatening condition caused by bacteria getting into the body. The symptoms start suddenly and worsen quickly. The signs can include a high temperature, flu-like symptoms, feeling sick or vomiting, diarrhoea, a widespread rash, dizziness, fainting, confusion or difficulty breathing. The lips, tongue and whites of the eyes may also turn bright red.

Necrotising fasciitis

The symptoms of necrotising fasciitis - a rare and life-threatening condition - can develop quickly within hours or over a few days. The initial symptoms can include extreme pain or loss of feeling near to a cut or wound, swelling of the skin around the affected area, a high temperature, headaches and exhaustion.

Symptoms that develop later can include being sick, diarrhoea, confusion, and black, purple or grey blotches and blisters on the skin.

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How can you get invasive Group A strep?

Strep A is spread by close contact between individuals, either by breathing out droplets from coughs or sneezes, or by direct skin contact. It can also be transmitted by contact with contaminated objects, such as towels or bedding. Outbreaks can sometimes happen in places like schools and care homes.

iGAS occurs when bacteria are able to cross through the body's natural defence mechanisms such as open wounds which can allow the bacteria to get into the tissue and bloodstream.

Having a long-term illness - a health condition that affects the immune system, such as HIV - can leave people at higher risk of invasive Group strep A. Among children, chickenpox is a risk factor1.

Some strains are more invasive than others. This does not seem to be the case in the outbreak in 2022. Since COVID-19 restrictions eased, there are more opportunities for infections like this to spread. It's believed infection rates are currently higher than previously seen at this time of year because people are mixing more.

How to prevent strep A

Good hygiene is essential in order to stop the spread of bugs, including streptococcus bacteria. You should teach your child how to wash their hands properly with soap for 20 seconds and encourage them to use a tissue to catch coughs and sneezes. If they become unwell, keep them away from others to reduce the risk of spreading infections.

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What should you do if you think your child has invasive Group A strep?

Urgent, early medical help is essential for iGAS. People rapidly become unwell between 12 and 24 hours. It is usually treated with antibiotics such as penicillin. However, how it is treated can depend on the severity of the illness and the complications2. It's important not to panic, however, as iGAS is rare.

The UK Health Security Agency advises to contact NHS 111 or your doctor if your child seems unwell and is getting worse. It's also important to seek medical help if your child is feeding or eating much less than normal, has had a dry nappy for 12 hours or more, or has a temperature of 38°C or higher.

You should call 999 (in the UK) if your child is having difficulty breathing, your child's skin, tongue or lips are blue or your child is floppy and won't wake up or stay awake3.

Further reading

  1. Coleman: The association between varicella (chickenpox) and group A streptococcus infections in historical perspective.

  2. Allen et al: Invasive group A streptococcal disease: Management and chemoprophylaxis.

  3. UK Health Security Agency: UKHSA update on scarlet fever and invasive Group A strep.

Article history

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

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