GBS 2021-11-17T16:07:14+00:00

About group B streptococcal infections

Group B Streptococcus (GBS) are bacteria related to (but not the same as) the group A streptococcus (sore throat or flesh-eating bug) which look like small round beads under the microscope and which produce a range of toxins and surface proteins which combat the human immune system and also cause disease. Group B streps (GBS) have been studied extensively because they can cause serious disease in newborn babies; much less is known about disease in adults. The group B strep is also known as Streptococcus agalactiae.

Group B strep normally live in people’s intestinal tracts and genital tracts without causing any problem; this may be commoner in pregnancy and anyway may vary from week to week. It is believed that babies become coated (‘colonised’) with the bug at the time of birth, as they pass through the birth canal (either from bugs in the intestinal tract or the vagina). Some women may be more at risk of being colonised than others, and doctors are trying to work out a way of identifying those who might benefit from antibiotics to clear colonisation just in time for delivery. Babies can also pick up the bug after delivery, usually from their mother or main carer Very occasionally, the bug can be transmitted from baby to baby via carers in a nursery setting.

Group B related necrotising fasciitis

Necrotising fasciitis can be caused by a number of bacteria, though the group A strep is a leading cause in about half of all cases that arise in the community setting. Group B strep can also cause this condition, though very rarely.

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 that are not dead.

Streptococci tend 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 strep necrotising fasciitis, surgery to remove all dead tissue is essential, along with antibiotics that kill all the likely bacteria.

Skin and soft tissue infection

Group B streptococcus (GPB) can cause serious skin infections, though mainly in diabetics and those with other serious medical conditions. If 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. The GBS 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, at least initially. Outpatient intravenous therapy is increasingly used for many cases. It is very difficult to grow bacteria from cases of cellulitis, 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), but group B strep can also cause this condition. 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.

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.

Group B streptococcal infections in adults

Group B streptococci can cause invasive disease in adults, though mainly in adults with predisposing factors, in particular those with diabetes (11-49%), cancer, alcoholism, HIV infection, the bedridden/elderly, or pregnancy.

GBS infection in adults include

  • Puerperal sepsis (infection in women at/around the time of childbirth)
  • Bacteremia (blood poisoning) with no source found
  • Pneumonia
  • Skin and soft tissue infection
  • Endocarditis (heart valve infection)
  • Bladder or kidney infection

The most common sources for bacteremia (blood poisoning) in non-pregnant adults are pneumonia, soft tissue infections (including wound infections), and the urinary tract/bladder, although bacteremia without identified source is also common.

Amongst pregnant women, the risk of invasive group B streptococcal bacteremia is also increased; pregnant women account for approximately a fifth of all cases of GBS bacteremia amongst adults. Antibiotic prophylaxis used to prevent infection of the newborn can also prevent GBS infection spreading in the mother.

Puerperal sepsis/infections of the female genital tract

This type of infection usually arises within the first two days of delivering a baby. Mothers may have infection of the womb (endometritis) or a wound infection at, for example, the site of a caesarean section. Occasionally, all that is found, are bacteria in the bloodstream, associated with a high fever. Although easily treated with antibiotics, doctors must ensure that the womb has been fully emptied following delivery, in case any left over tissue is acting as a focus for the infection; this sometimes means that a special scan is necessary, or a small operation to empty the womb. Occasionally, the condition is complicated by an abscess (pus collection) in the abdomen which would require drainage, or by septic shock.


Group B strep can cause infection of the lung tissue; whether the bugs reach the lung directly from the throat, or whether they reach the lung via the bloodstream is unknown (and may vary from case to case). Pneumonia due to these types of streptococci is rare but can be associated with bacteremia (bacteria spreading into the bloodstream) and septic or toxic shock.

Bone and joint infection

GBS can spread from the blood (or skin) into joints , often those that are previously damaged by injury or arthritis and especially in diabetics. This may cause swelling, redness, and pain over the joint. Sometimes, the joint infection (arthritis) spreads into the bone, causing ‘osteomyelitis’. This type of infection requires prolonged antibiotic treatment, alongside drainage of any pus around the joint or bone.

Urine and bladder infections

GBS is a common cause of cystitis in women, and can also cause a more serious infection of the upper urinary tract, to include the kidney. This normally only occurs in people with poor immunity e.g. diabetics, or in pregnant women.


This is a particularly risky but rare infection that involves the heart valves. People who have previously damaged heart valves through, for example, rheumatic fever, are most at risk. The bacteria form clumps on the valves which can ‘fly off’ to cause serious problems such as a stroke or damage to other organs, Treatment will involve several weeks of intravenous antibiotics and sometimes surgery is essential to cure the condition.

Rarer deep infections caused by GBS

Occasionally, GBS can cause infections like meningitis (infection of the lining of the brain), infection of the abdominal cavity (peritonitis), or eye (ophthalmitis). 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.

Bacteremia and Septicaemia

The appearance of bacteria in the blood stream is a serious indicator of deep-seated 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 which bug 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 due to strep will be, that the blood culture is positive and grows a strep, usually the following day or two days later. Special tests will be done to check which group the strep belongs to (i.e. group A, B, C, F, or G) Doctors may have started antibiotics using a ‘best guess’ approach. Fortunately, streps are killed by most of the antibiotics commonly used in a wide range of conditions.

Bacteremia is usually seen only in cases of invasive or deep infection. Occasionally, doctors cannot work out the site of a strep infection in the body, but will try and investigate using blood tests and scans. This is important because a patient might need surgery in addition to antibiotics.

Group B streptococcal infections in newborn babies

Up to a third of all men and women carry GBS in their intestines without symptoms and roughly a quarter of women of childbearing age carry GBS in the vagina at any one time. GBS is a normal body commensal (an organism that lives on another without harming it). A positive swab result for GBS means a woman is colonised with GBS at the time the swab was taken – not that she or her baby will become ill.

GBS colonisation is normal and does not require treatment with antibiotics. The time when antibiotics are effective against GBS infection in newborn babies is when they are given intravenously (through a vein) to a pregnant woman when she goes into labour or her waters break.

If GBS is found in the urine, this should be treated at the time of diagnosis with oral antibiotics and the treatment repeated if necessary until urine tests come back clear. This is also an indication that the pregnant woman should be offered intravenous antibiotics once labour starts or her waters break. At least 6 out of every potential 10 cases – this saves lives!

Much more information can be found at the Group B Strep Support website.

GBS infections

In newborn babies with early onset (first five days) GBS can cause

  • Bacteremia (bacteria in the blood/blood poisoning)
  • Pneumonia
  • Meningitis

In newborn babies with later onset (up to 3 months old) GBS can cause:

  • Bacteremia
  • Meningitis

Preventing newborn GBS disease

Full details can be obtained from the group B strep support group. Some countries have started giving ‘preventative’ (prophylactic) antibiotics to women known to be colonised with GBS or those assessed to be at high risk, to prevent transmission to the newborn baby. Though still controversial in the U.K. the programme has resulted in a sizeable reduction in early onset neonatal GBS infection in the U.S.A. In the UK, at present, anyone known to be at risk of GBS carriage in pregnancy (e.g. having had a previous GBS-infected baby or having had an earlier swab showing GBS) is given antibiotic prevention. However, there is no screening programme in the UK. It is possible to be screened for GBS carriage in pregnancy and details can be found on the GBS support group website. Efforts are being made to develop a vaccine against GBS but at present there is no licensed vaccine that works.