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All about Streptococcus A

Streptococcus A – or strep A as it’s most commonly referenced – has hit the headlines recently as infections caused by this bacterium. Strep A causes a number of different infections and is responsible for scarlet fever. Between September 2022 and March 2023 alone, there were 49,372 scarlet fever notifications in the UK, which is high. Invasive group A streptococcus (iGAS) infections are also high, with 2,415 cases in the same period. This article will tell you everything you need to know about streptococcus A.

What is streptococcus?

Streptococcus is a group of bacteria belonging to the Streptococcaceae family. The term itself comes from the Ancient Greek streptós, which means “twisted” and kókkos, meaning “grain” or “berry”. The name derives from the fact that the bacteria grow in pairs and resemble a chain of berries.

This type of bacteria is characterised microbiologically as being nonmotile, which means it cannot move. They are also gram-positive. This means the cell walls of the bacteria are thick and they don’t have an outer membrane.

Streptococcus bacteria grow in these chains because when they undergo cell division, the cells don’t separate completely.

They are a common pathogenic bacterium responsible for a number of conditions:

  • Streptococcus pneumoniae – This is the most common cause of pneumonia and is also the cause of many sinus infections, conjunctivitis (pink eye) and bacterial meningitis.
  • Streptococcus pyogenes (group A strep) – This is the cause of strep throat, cellulitis, pharyngitis, impetigo, scarlet fever, necrotising fasciitis, glomerulonephritis and rheumatic fever.
  • Streptococcus agalactiae (group B strep) – This is usually an infection in newborns and causes sepsis, pneumonia, meningitis and pyarthrosis.
Suffering from strep a bacteria

What is group A streptococcus?

Group A streptococcus is also known as group A strep, strep A, GAS and Streptococcus pyogenes. This is a bacterium that can colonise in the skin, anogenital tract and the throat. The bacteria spread through close contact, including skin contact and respiratory particles. Strep A can also be transmitted in the environment by contact with contaminated surfaces like bedding or by eating food prepared by an infected person.

It causes a range of infections and illnesses.

What is invasive group A streptococcal disease?

On rare occasions, the disease-causing streptococcal bacteria can make their way into areas like fatty tissue, deep muscles, the lungs and the bloodstream. This causes an infection called invasive group A streptococcus or iGAS. Most people who have GAS don’t go on to develop iGAS.

This happens when the bacteria manage to cross through the body’s defence mechanisms via open wounds, for example. People are more at risk if they have a condition that affects their immune system like HIV. It can also happen in children with chickenpox too.

Those most at risk of iGAS include:

  • Infants and children under the age of five.
  • Over 65s.
  • Indigenous people.
  • Those living in crowded or unhygienic conditions.
  • Those with a chronic illness like diabetes, cancer, heart disease, liver disease, kidney disease or lung disease.
  • Those who consume alcohol heavily (binge drinking or heavy drinking over time).
  • Those will soft tissue and skin infections (e.g., cellulitis).
  • Those who use steroid medications long term.
  • Children who have had chickenpox in the last two weeks.

From this, the most severe complications are necrotising fasciitis and streptococcal toxic shock syndrome (STSS).

Necrotising fasciitis

Necrotising fasciitis is a life-threatening yet rare disease. It can come on within a matter of hours but it might take a few days to develop. Initially, the person will have feelings of extreme pain at the infected site. Sometimes, though, there might actually be a loss of feeling instead. The site might be a wound or skin swelling. Other symptoms include high temperature, headaches and feelings of exhaustion.

Later symptoms include confusion, vomiting and diarrhoea and purple, black or grey blisters and blotches on the skin. Essentially, necrotising fasciitis destroys the tissue and skin, which is why it has been referred to as a flesh-eating disease.

When it is caused by strep A, this condition is known as type 2 necrotising fasciitis and it is the most common one to infect otherwise healthy people.

Toxic shock syndrome

Like necrotising fasciitis, toxic shock syndrome is a life-threatening rare disease. It causes a drop in blood pressure, which then leads to organ failure.

Its symptoms tend to come on suddenly and will worsen very quickly. Symptoms of streptococcal toxic shock syndrome include flu-like symptoms, fever, nausea and vomiting, diarrhoea, rash, fainting, dizziness, difficulty breathing and confusion. You might also notice the whites of the eyes and the lips and tongue turning bright red.

Who is at risk of a GAS infection?

GAS infections are most common in children but adults can be infected too. You’re more at risk of getting group A strep if you have a weakened immune system or have open wounds or sores.

A weakened immune system can be caused by a number of things including:

  • Treatment for cancer (chemotherapy).
  • Drugs used post-operatively following an organ transplant to prevent rejection.
  • Poor nutrition.
  • Excessive alcohol consumption and smoking.
  • Autoimmune diseases like Type 1 diabetes, rheumatoid arthritis, lupus, etc.

Infections caused by strep A?

Group A streptococcus is responsible for a range of respiratory, soft tissue and skin infections.

These include:

  • Tonsilitis (strep throat) – This is a common infection that makes the tonsils swell and become red. If this is caused by bacteria, antibiotics are usually needed.
  • Pharyngitis – This is inflammation of the pharynx, which is the part of the throat behind the nasal cavity and the mouth. Pharyngitis causes discomfort, pain, difficulty swallowing and a scratchy feeling.
  • Impetigo – This is a skin infection that isn’t usually serious but is very contagious. With treatment, it improves within a week or ten days. It starts with blisters or red sores that turn into yellowy crusts. It’s most common on the face, legs and arms.
  • Scarlet fever – This is a contagious disease that affects young children mostly. It is treated with antibiotics and presents with flu-like symptoms, a red sandpaper rash and a ‘strawberry’ tongue.
  • Cellulitis – This is a skin infection that can be serious if it isn’t treated. It presents as a red area that’s swollen. The area might feel hot and is usually painful.
  • Pneumonia – This is an infection of the air sacs in the lungs. It presents as a severe wet cough and is accompanied by fever and problems with breathing.
  • Erysipelas – This is a common skin infection that causes a raised, tender and red rash on the skin, usually on the face and legs.
  • Bacteraemia – Bloodstream infections.
  • Rheumatic fever – Inflamed tissues in the heart and joints.
Undergoing chemotherapy making person more at risk

Symptoms of strep A infections?

The symptoms of strep A infections will vary depending on which illness the bacteria has caused.

Mild symptoms include:

  • Difficulty with swallowing or pain associated with swallowing (this is common with strep throat, tonsilitis and scarlet fever).
  • Headache.
  • Red spots (petechiae) on the roof of the mouth.
  • Pain in the stomach.
  • Swollen lymph nodes or tonsils.
  • Symptoms of skin infection (red skin, oozing skin etc.)
  • Rashes (usually on the groin, underarms, neck or face).
  • Purple or red sores on the legs, arms, mouth and nose.
  • Itchy skin.
  • Skin sores that leak pus or a clear or yellow fluid.
  • Skin sores with yellow crusts.

Severe symptoms include:

  • Dizziness.
  • Diarrhoea.
  • High temperature.
  • Large wounds and blisters, including black spots on the skin.
  • Nausea.
  • Vomiting.
  • Severe pain beyond any skin wounds.
  • Changes in skin colour.
  • Skin that feels warm or hot.
  • Swollen skin.

How do you get strep A infections?

Group A streptococcus bacteria is very contagious. When someone is infected with the bacteria, they can easily spread it to other people.

Spread can occur in a range of ways, including:

  • Close contact with the infected person.
  • Breathing in bacteria released after an infected person has sneezed or coughed.
  • Coming into contact with the bacteria by sharing utensils or cups with an infected person.
  • Touching an infected sore or wound on the skin.
  • Using the same bath towels as an infected person.

How to prevent a streptococcus A infection

You are most likely to contact the bacteria when an infected person has symptoms. For this reason, it’s a good idea for infected people to stay home and treat their infection either with antibiotics or skin treatments as recommended by the doctor.

There isn’t a vaccine against group A strep infections but it is possible to reduce your chances of catching the bacteria with good hygiene.

This includes:

  • Washing hands with warm water and soap frequently.
  • Using hand sanitiser when handwashing facilities aren’t available.
  • Catching coughs and sneezing and throwing away tissues.
  • Avoiding close contact with those who are sick.
  • Cleaning skin wounds and sores and keeping them covered until they’re fully healed.

Diagnosing streptococcus A infections

Diagnosing strep A will depend upon the symptoms present and the type of infection. If you think you have GAS, your GP will check the symptoms and carry out a physical examination. You will be asked about the symptoms, how long they have been present and their severity.

You might be offered tests to confirm a diagnosis.

This could include:

  • A blood test that looks for infection.
  • A culture test that looks at throat swabs under a microscope. This might be used for strep throat and scarlet fever, for example.
  • A biopsy of a tissue sample to look for infection. This is for GAS infections of the skin.
  • An ultrasound, CT scan or MRI to see if there is any damage to the tissues underneath the skin that has been caused by the strep infection.

Treatments for streptococcus A

Most group A streptococcus infections are treated with antibiotics and the type of antibiotics prescribed will depend on the type and location of the infection. For skin infections, a topical antibiotic will be given as a cream to rub onto the sores. This might also be accompanied by oral antibiotics depending on how serious the infection is.

For other strep infections like scarlet fever, a course of antibiotics is given. It’s important to complete the whole course even when symptoms improve.

For serious strep A infections like invasive group A strep, the person might need to be admitted to hospital for treatment with intravenous antibiotics. Some people with iGAS require treatment in intensive care.

As well as treating the infection, antibiotics will also shorten the illness and minimise symptoms. What’s more, they also prevent the spread of the bacteria. When you have been taking the antibiotics for 24 hours (or using topical antibiotics for 24 hours), you are deemed to no longer be contagious.

Finally, using antibiotics also prevents the infection from becoming worse and, therefore, wards off potential complications.

There are several types of oral antibiotics you could be prescribed for a strep A infection:

  • Penicillin
  • Amoxicillin
  • Benzathine

For those allergic to penicillin, there are alternatives like azithromycin.

Taking antibiotic to treat strep a

Delayed problems caused by strep A

After infection, strep A can cause delayed problems. These problems used to be more common but thanks to antibiotics and improved hygiene, they’re much rarer.

Delayed problems include:

  • PANDAS (paediatric autoimmune neuropsychiatric disorders associated with streptococcal infections).
  • Post-streptococcal glomerulonephritis.
  • Rheumatic fever.


This describes a condition when children develop symptoms of mental health problems and obsessive-compulsive disorder (OCD) suddenly following an infection with streptococcal A. There is a theory that the infection leads to an autoimmune condition leading to PANDAS – though this is controversial as no definitive link between the two has been proven. There are no diagnostic tests that can confirm this condition.

Post-streptococcal glomerulonephritis

This condition is a problem with the kidneys. It is believed to be caused by a previous group A strep infection that has led to an autoimmune response. Normally, this condition will get better without treatment. As such, any treatment given tends to be focused on managing symptoms and preventing complications. Symptoms that are treated might include high blood pressure.

Rheumatic fever

This occurs when the strep A infection causes an autoimmune response. Rheumatic fever causes a range of problems, including nerve, joint and heart inflammation. Though it has been almost eradicated in the United Kingdom and other developed nations, it is still a problem in certain parts of the world like the South Pacific, Central Asia, South Asia, the Middle East, and sub-Saharan Africa.

Final thoughts on streptococcus A

Though strep A infections have been on the rise in the last twelve months, they do tend to fluctuate in waves. The previous high season for infections was in the 2017-2018 season and four under-10s died from invasive group A strep infections. Nobody really understands why the waves occur.

However, the rates did drop significantly around the time that COVID-19 measures were in place. This is not surprising given that this virus is transmitted in the same way. There are theories suggesting that the recent rise in strep A cases could be because children were not exposed to the bacteria due to the COVID-19 measures and, as such, didn’t build up an immunity to it.

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About the author

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Louise Woffindin

Louise is a writer and translator from Sheffield. Before turning to writing, she worked as a secondary school language teacher. Outside of work, she is a keen runner and also enjoys reading and walking her dog Chaos.

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