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All about Streptococcus B

Between 20% and 40% of women carry streptococcal B bacteria naturally with no ill effects. This is usually in their gut, rectum or vagina. Carrying this bacterium is completely normal and there are no side effects. It does not need to be treated and you’re not classed as having a disease if you do have the bacteria. However, the presence of these bacteria can cause problems for newborn babies. Around one baby in 1,750 is diagnosed with an early-onset group B strep infection while one in 2,700 is diagnosed with a late-onset infection.

In this article, we’ll tell you all about streptococcus B.

What is streptococcus?

The term ‘streptococcus’ refers to bacteria from the Streptococcaceae family. Meaning ‘twisted berry’ in Ancient Greek, it is so-called due to how the bacteria grow in chain-like pairs that resemble berries. Microbiologically speaking, streptococcus is nonmotile (it can’t move) and is gram-positive.

Being gram-positive means the bacteria have certain features like thick cell walls with no outer membrane.

Streptococcus bacteria are chained because their cells don’t completely separate during cell division. They’re responsible for a number of different conditions and there is more than one type of streptococcus bacteria.

Here are the different types of streptococcus bacteria:

  • Streptococcus Group A (Streptococcus pyogenes) – the cause of cellulitis, impetigo, scarlet fever, strep throat, necrotising fasciitis, rheumatic fever and glomerulonephritis, among others.
  • Streptococcus Group B (Streptococcus agalactiae) – the cause of newborn infections, pneumonia, sepsis, meningitis and pyarthrosis.
  • Streptococcus pneumoniae – the cause of sinus infections, pneumonia, pink eye (conjunctivitis) and bacterial meningitis.
New born infection

What is group B streptococcus?

As mentioned above, this group B is a type of streptococcal bacteria. For adults carrying the bacteria naturally in their body, it is typically harmless and causes no symptoms. Where we do need to be concerned about the bacteria is when a woman is pregnant or has a newborn, and in the elderly or someone who is very ill already.

It can cause urinary tract infections (UTIs), bacterial pneumonia, meningitis, blood infections (bacteraemia) and soft tissue, skin, joint and bone infections.

What is the difference between strep A and strep B?

Both strep A and strep B are two species of the Streptococcus bacterial genus. Strep A refers to Streptococcus pyogenes while strep B refers to Streptococcus agalactiae.

They are both caused by beta haemolysis, which means the complete breakdown of red blood cells, and both are chained and gram-positive.

There are, however, differences between the two. Strep A is aerotolerant, which means it can survive and grow in air. Strep B, on the other hand, is facultative anaerobic, which means it can survive and grow in both aerobic and anaerobic conditions. For this reason, strep A is generally found on the skin’s surface and within the throat while strep B is mainly found within the gut and vagina.

Besides these differences, the two bacteria cause different illnesses and problems. Strep A is known to cause tonsilitis, scarlet fever, cellulitis, and more. Strep B causes severe neonatal infections, UTIs and mastitis in cattle.

Who is at risk of streptococcus B?

Group B strep (also known as GBS) rarely causes problems and you can be a carrier of the bacteria without it causing you any symptoms, problems or disease. However, pregnant women who have group B strep can pass the bacteria on to their babies.

Newborn babies are particularly susceptible to problems caused by strep B. Most babies are healthy; however, 1 in 1,750 babies contract the bacteria from their mother during their birth. This does, unfortunately, lead to a small number of neonatal deaths.

Several factors are known to increase the risks of having a baby that goes on to develop group B strep disease.

This includes:

  • Testing positive for group B strep in late pregnancy (36-37 weeks).
  • A fever developing during labour.
  • Having over 18 hours in between waters breaking and a baby being born.

Besides infants, older adults or people who have chronic health conditions are at risk of problems too. This includes skin infections, cellulitis, UTIs, pneumonia, joint and bone infections, endocarditis, and meningitis.

Those who are more at risk of GBS disease include:

  • Adults with diabetes.
  • Adults with heart disease or congestive heart failure.
  • Adults with cancer (or a history of cancer).
  • Obese adults.
  • Adults over 65 years of age.

Pregnant women

Although many pregnant women can and do carry group B strep bacteria asymptomatically, they do have an increased risk of infection too. In pregnancy, group B strep is a common cause of UTIs.

GBS can also cause chorioamnionitis, which is an intra-amniotic infection. This condition is so-called due to the location of the infection: within the membranes and tissues that surround a foetus – the chorion and the amnion. It can also affect the amniotic fluid and the placenta too. With this infection, antibiotics are usually given. It might even be required to deliver the baby early as it can result in life-threatening complications for both the baby and the mother. Besides group B strep, E. coli is another cause.

Pregnant women can also suffer from postpartum endometritis or bacteraemia due to carrying GBS. Postpartum endometritis is an infection in the endometrium – the lining of the uterus. With this infection, the lining becomes inflamed and swollen. It is more common following a caesarean section.

Types of streptococcus B infections

There are a number of different problems caused by strep B.

In adults, you can have the following problems:

  • Urinary tract infections.
  • Blood infections (bacteraemia).
  • Pneumonia.
  • Soft tissue or skin infections.
  • Joint or bone infections.

Babies can become critically ill straight after birth (early onset) or within the weeks and months following birth (late onset).

Suffering from UTI from strep B

Symptoms of strep B

A strep B infection will have different symptoms depending on who is infected and where the infection is located.


Most babies who contract strep B remain healthy. However, some do get critically ill after contracting the infection during their birth.

The signs and symptoms of a strep B infection are as follows:

  • Low body temperature.
  • Fever.
  • Problems feeding.
  • Poor muscle tone, limpness or sluggishness.
  • Irritability.
  • Difficulty with breathing – this might include slow or fast breathing.
  • Seizures.
  • Jitteriness.
  • Jaundice.
  • Presence of a rash or changes in skin colour.


Adults are much more likely to carry the bacteria naturally in their bodies without any problems. Some, however, will develop a strep B infection, like the elderly or people who have another condition that lowers the strength of their immune system.

Adult symptoms depend on the type of infection the strep B has caused:

For UTIs, the symptoms are:

  • A persistent and strong urge to urinate.
  • Pain or burning during urination.
  • Passing urine frequently in small amounts.
  • Blood in the urine – the urine might be pink, red or brown.
  • Pelvic pain.

For a blood infection, the symptoms include:

  • Chills.
  • Fever.
  • A lack of alertness or confusion.

Pneumonia symptoms present as:

  • Chills.
  • Fever.
  • Cough.
  • Chest pain when coughing or breathing.
  • Shortness of breath.

Soft tissue and skin infections present as:

  • Pain.
  • Lesions with drainage or pus.
  • Redness, warmth or swelling.

Joint and bone infections have the following symptoms:

  • Pain.
  • Redness, warmth or swelling.
  • Chills.
  • Fever.
  • Stiffness or being unable to use the joint or limb.

Causes of streptococcus B

A group B streptococcus infection (also known as GBS) is caused by Streptococcus agalactiae bacteria. This is naturally found in the gut, rectum and vagina. GBS is not a sexually transmitted infection (STI).

Diagnosing group B strep

If a group B strep infection is suspected, tests will be carried out to confirm. It might be that antibiotic treatment is started before the results come back – for example, in babies.

Tests carried out include tests on body fluids like spinal fluid and blood. Doctors will test to see if there is any growth of bacteria in the samples taken. This will take a few days to determine as the bacteria will need to grow. There might also be chest X-rays taken or samples of urine tested, as group B strep bacteria is known to cause bladder infections and UTIs.

Risks of streptococcus B

Strep B infections are riskier in babies as well as adults with some chronic medical conditions like liver disease and diabetes. The elderly are more at risk too.

If a woman is carrying group B strep bacteria while she is pregnant, there is a chance that the baby could contract the bacteria during the birth. Most babies who do get strep B from their mothers are healthy and make a full recovery. However, some babies do become critically ill with problems like meningitis and sepsis. Resulting problems can be vision loss or hearing loss. Unfortunately, strep B infections can be fatal. In the United Kingdom, around one baby each week will die from strep B and another will be left with a long-term disability. Statistics-wise, between 4% and 6% of babies who get a GBS infection will die.

Data has also shown that the rate of infection in babies has risen by 77% since 1996. The figure in England is more than double that of lots of other high-income countries – and this is largely down to the fact that other countries have introduced screening for group B strep during pregnancy.

Besides babies, serious GBS infections can affect adults. In terms of averages, around 5% of adults who develop a group B strep infection will die.

Preventing streptococcus B

The best way to prevent a strep B infection in newborns is to identify the infection in pregnant women and treat it with antibiotics. Any woman who tests positive for strep B will be given appropriate treatment so that it doesn’t get passed on to their baby during birth.

In Australia, Canada and the US, all women are tested for GBS late into their pregnancy. In the US, for example, women are tested for the bacteria at 36 or 37 weeks pregnant. For those who test positive, IV antibiotics can be given during labour.

Unfortunately, routine testing is not carried out in the UK and a test for group B strep is rarely carried out on the NHS, though it is possible to get one done privately.

How group B strep spreads

The spreading of group B strep bacteria is pretty much undetermined among the general population. It is known that pregnant women carrying the bacteria can pass it on to their babies during birth. It is not known, however, how babies that develop late-onset group B infections come to contract the bacteria.

Like many bacteria, however, it is likely that group B strep is passed on through direct contact like kissing, hand contact and close physical contact. Since it is found in the vagina and rectum, it could also be passed on through sexual contact. It is not, however, a sexually transmitted infection.

Pregnant with IV antibiotics

Treatment for strep B

If a pregnant woman has been found to have strep B, either during her current pregnancy or a previous one, she will be advised by her midwife or consultant on how to treat it. In these cases, it’s often recommended to give birth in a hospital rather than at home.

As soon as the mother’s waters break or they go into labour, the woman should contact their midwife. Typical treatment involves having intravenous antibiotics during labour as this can reduce the risk of the baby contracting a strep B infection.

When a baby develops symptoms, they will be given intravenous antibiotics.

If there is a bone or soft tissue infection, there might be other treatment needed, like surgery.

Final thoughts on group B strep

To summarise, group B strep is a type of streptococcal bacteria that is very common. This bacterium is normally carried harmlessly without people realising they have it. GBS is only a problem when it affects pregnant women, young babies, people who are ill, or the elderly. A diagnosis of group B strep will be followed by antibiotics. Unfortunately, some babies and adults will die from a group B strep infection, though this is very rare.

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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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