Streptococcal infections are any type of infection caused by the Streptococcus ('strep') group of bacteria.

There are many different types of Streptococci and infections vary in severity from mild throat infections to pneumonia. Streptococcal infections are usually treated with antibiotics.

Streptococci are divided into two key groups:

  • alpha-haemolytic - made up of two groups, Streptococcus pneumoniae and Viridans Streptococci
  • beta-haemolytic - made up of Group A and Group B Streptococci

This topic focuses on the beta-haemolytic group of Streptococci. Read about pneumococcal infections for information on infections caused by Streptococcus pneumoniae.

Group A and Group B strep


Group B strep (strep B) usually live harmlessly inside the digestive system and, in women, the vagina. Strep B tend to only affect newborn babies and usually cause more serious types of infection.

These two groups are described in more detail below. You can find information on the symptoms, causes and treatment of specific infections by following the links provided.

Strep A

Minor strep A infections

Most infections caused by strep A are unpleasant but do not usually pose a serious threat to health. They include:

  • throat infection at the back of the throat, known as pharyngitis, which can cause swollen glands and discomfort when swallowing
  • impetigo - a skin infection which can cause blistering of the skin around the nose, mouth, arms, trunk or legs
  • cellulitis - an infection of the deeper layers of the skin, which most commonly affects the legs
  • a middle ear infection, which often causes earache, a high temperature and some temporary hearing loss

Invasive strep A infections

Strep A bacteria only pose a potentially serious threat to health if they penetrate deeper inside the tissues and organs of the body and trigger what is known as an invasive infection. Examples of invasive infections include:

  • pneumonia - an infection of the lungs that causes persistent coughing, breathing difficulties and chest pain
  • sepsis - an infection of the blood that causes a high temperature, rapid heartbeat and rapid breathing

Diagnosing a strep A infection

Strep A infection can be diagnosed by taking a swab of affected tissue or saliva and checking it for the presence of bacteria. A blood test can also be used later on in the illness to check if your immune system has produced certain antibodies in response to a strep A infection.

If an invasive group A infection is suspected, blood tests can be used to confirm whether there are actually bacteria in the blood, rather than just the antibodies.

Who is at risk of a strep A infection?

Minor strep A infections are common. One estimate is that one in every four sore throats is caused by a strep A infection.

People of any age can be affected by a throat infection, sinusitis or cellulitis. Impetigo and inner ear infections are most common in children younger than 15.

More serious invasive strep A infections are much rarer. It is estimated that only 1 in every 33,000 people will develop an invasive infection in any given year in England. They usually affect people with a weakened immune system, such as:

  • babies aged less than six months
  • those over 75 years of age
  • those with a health condition that weakens the immune system, such as HIV, cancer or type 2 diabetes 
  • those who inject drugs such as heroin
  • those who misuse alcohol
  • pregnant women

There are a number of medical treatments that can also weaken the immune system, such as:

Treating a minor strep A infection

Some minor strep A infections, such as a throat infection or inner ear infection, will often get better on their own without the need for treatment. 

Paracetamol or  non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen may be used to control any pain and fever. However, there is some evidence to suggest that NSAIDs can increase the risk of an invasive infection. This may be due to NSAIDs masking more severe symptoms, or delaying the immune system's response to infection.

Aspirin should not be given to children aged under 16.

Minor infections of the skin will usually require treatment with antibiotic tablets or creams.

Most people with a minor strep A infection will make a full recovery and experience no long-term complications.

Treating an invasive strep A infection

Invasive strep A infections (with the possible exception of pneumonia) are regarded as a medical emergency and you'll need to be admitted to hospital. You may need to be placed in an intensive care unit while medical staff treat the infection.

The infection is usually treated with injections of antibiotics for 7-10 days. In some cases, surgery may be needed to remove or repair damaged tissue. Occasionally, a blood transfusion may be used to help neutralise toxins produced by the bacteria.

The outlook for more serious invasive strep A infections is poor, especially as most people who develop this type of infection have a weakened immune system. It is estimated that 1 in 4 people who develop an invasive strep A infection will die from it.

Strep B

Most people quickly develop a natural immunity to strep B, so these types of infection are much rarer and tend only to affect newborn babies.

Strep B in pregnancy

It is estimated that 1 in 5 pregnant women have strep B bacteria in their vagina and/or digestive system. The bacteria can sometimes be passed on to the baby through the amniotic fluid (a clear liquid that surrounds and protects the unborn baby in the womb). Strep B infections are thought to affect 1 in every 2,000 births.

It is also possible for a baby to contract a strep B infection as it passes through the birth canal during labour.

Strep B in newborn babies

The symptoms of a strep B infection in a newborn baby usually develop within the first 12 hours of giving birth and include:

  • being floppy and unresponsive
  • poor feeding
  • grunting when breathing
  • irritability
  • an unusually high or low temperature
  • unusually fast or slow breathing
  • an unusually fast or slow heart rate

In some cases a baby can catch an infection a few months after birth, known as a late-onset group B strep infection. There is often no obvious reason why this happens, but known risk factors include:

  • being born prematurely
  • being part of a multiple birth – for example, twins or triplets
  • having a mother with a history of group B strep infection

Treating a strep B infection

As newborn babies have a poorly developed immune system, the bacteria can quickly spread through their body, causing serious infections such as meningitis and pneumonia.

Healthcare professionals take a preventative approach to treating strep B infections by trying to identify babies at high risk of developing such infections and giving injections of antibiotics (intravenous antibiotics) to the mother during labour. Alternatively, the baby can be given intravenous antibiotics shortly after birth.

Known risk factors that may mean you need injections of antibiotics during labour include:

  • you have a high temperature during labour
  • you go into labour prematurely

The preventative approach is used because although survival rates have improved significantly in recent years, 1 in every 10 babies with a strep B infection will die.

If your baby has symptoms that suggest a strep B infection, a diagnosis can be confirmed using blood and urine tests and they will need to be treated with intravenous antibiotics.

Pharyngitis is a common streptococcal infection 

Viridans Streptococci

Viridans Streptococci are another type of Streptococci bacteria, mostly found in the mouth, gut and genital region.

Viridans infections are most serious if the bacteria enters other areas of the body. For example, if Viridans gets into the bloodstream it can cause endocarditis (infection of the inner lining of the heart).

People most at risk of a Viridans infection include those with damaged heart valves, other heart problems or a weakened immune system.

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Page last reviewed: 21/03/2013

Next review due: 21/03/2015