What are Streptococcal infections?

Streptococcal infections are any type of infection caused by the group of bacteria Streptococcus.

  • There are many different types of Streptococci and infections vary in severity from mild throat infections to pneumonia.
  • Streptococcal infections are primarily treated with antibiotics.
  • Streptococci are divided into two key groups: 
    • alpha (α)-haemolytic Streptococci
    • beta (β)-haemolytic Streptococci.

α-haemolytic Streptococci

  • This group is very common.
  • Many strains live naturally in humans causing no symptoms.
  • α-haemolytic Streptococci are split into two groups:
    • Streptococcus pneumoniae
    • Viridans Streptococci.

Streptococcus pneumoniae

  • S. pneumoniae is usually found on the surface of the skin and inside the throat.
  • It causes infections in both adults and children.
  • It is transmitted through coughs and sneezes.
  • Minor infections can be treated relatively easily with antibiotics and include:
    • sinusitis (inflammation of the sinuses)
    • middle ear infections.
  • More invasive infections pose a more serious threat to health and include:
    • pneumonia (inflammation of the tissue in the lungs)
    • meningitis (inflammation of the membranes covering the brain and spinal cord)
    • bacteraemia (infection of the blood).
  • People at the highest risk of invasive S. pneumoniae infections are:
    • babies under six months old
    • adults over 75 years old
    • adults with a weak immune system. 

A plate of Streptococcus pneumoniae.

Image credit: Nathan Reading on Flickr [CC-BY-2.0], via Wikimedia Commons

Viridans Streptococci

  • This group of Streptococci are most often found in the mouth, gut and genital region.
  • The most serious Viridans infections occur when the bacteria enters other regions of the body. For example, if Viridans gets into the bloodstream it can cause endocarditis (infection of the inner lining of the heart).
  • Individuals with damaged heart valves or cardiac abnormalities and compromised immune systems are at particular risk.
  • Symptoms include:
    • tiredness
    • weakness
    • fever
    • weight loss
    • respiratory problems
    • problems with heart function in cases where endocarditis occurs.

Diagnosis and treatment of α-haemolytic infections

  • Minor infections can be diagnosed by taking a sample of saliva or a swab of the affected tissue and testing for the presence of Streptococcal bacteria.
  • For invasive infections additional tests may be required, such as a blood test for bacteraemia or cerebral spinal fluid test for meningitis.
  • Minor infections may not require treatment or may be treated with antibiotics.
  • Invasive infections usually result in a hospital stay.
  • Severe invasive infections may require intensive treatment with intravenous antibiotics for 7-10 days. In some cases surgery may be required to remove or repair damaged tissue.

β-haemolytic Streptococci

  • β-haemolytic Streptococci are characterised as Group A Streptococci (GAS) and Group B Streptococci (GBS)

Group A (Streptococcus pyogenes)

  • Streptococcus pyogenes is transmitted through coughs, sneezes or direct contact
  • It can be either non-invasive (not spread into the bloodstream) or invasive (spread into the bloodstream and to other body sites)
  • The most common of the non-invasive infections include:
    • strep throat: sore throat specifically caused by streptococcal infection
    • impetigo: contagious skin infection that causes sores and blisters
    • scarlet fever: infectious disease causing a sore throat and characteristic red rash.
  • Invasive infections are much rarer and occur when the bacteria infects other areas of the body such as the blood and organs. This can result in:
    • pneumonia: inflammation of the tissue in the lungs
    • bacteraemia: infection of the blood
    • necrotising fasciitis: flesh-eating disease.
  • Left untreated, potential complications of Group A infection include rheumatic fever, a disease that affects the joints, kidneys and heart.

Diagnosis and treatment of Group A infections

  • For non-invasive infections a Rapid Strep Test (RST) can be carried out. This involves a doctor taking a throat or nose swab that is analysed for group A Streptococcus. An RST is one of the most common tests for this type of infection.
  • For suspected invasive infections a blood test may be taken.
  • Most infections are treated with antibiotics:
    • superficial skin infections can be treated with topical antibiotic ointments
    • other infections can be treated with oral or intravenous antibiotics depending on the severity of the infection.
  • Where the infection has caused a lot of skin damage, for example in cases of necrotising fasciitis, damaged tissue may be removed surgically.

Group B (Streptococcus agalactiae)

  • Streptococcus agalactiae usually lives harmlessly inside the digestive system and female genitals.
  • It can be transmitted sexually or from mother to baby during birth.
  • Group B β-haemolytic Streptococcus tend to only affect new born babies as the bacteria can be passed onto the baby from the mother through the amniotic fluid (protective fluid that surrounds the foetus in the womb).
  • Due to being continually exposed to it through our lifetimes most people quickly develop a natural immunity to Group B β-haemolytic Streptococcus.
  • Symptoms of group B β-haemolytic streptococcal infection in a newborn baby include:
    • being floppy and unresponsive
    • poor feeding
    • unusually high or low body temperature
    • unusually fast or slow heart rate
  • If left untreated, group B β-haemolytic streptococcal infections can also lead to much more serious conditions such as meningitis and pneumonia.
  • Factors increasing risk of group B β-haemolytic streptococcal infection in new-born babies include:
    • premature birth
    • being part of a multiple birth
    • having a mother with a history of group B streptococcal infection.

Diagnosis and treatment of Group B infections

  • These infections are diagnosed by a blood, urine or cerebral spinal fluid sample to identify the bacteria.
  • A culture of fluid from the vagina or rectum can also determine if a woman is infected.
  • The infection is treated with antibiotics, often directly into the bloodstream (intravenously).
  • Treatment of these infections may require a hospital stay.

Preventing Group B Streptococcal infection in newborns

  • Healthcare professionals take measures during labour and after birth to prevent newborns becoming infected with Streptococcus.  
  • If a baby is known to be at risk of Streptococcus infection, antibiotic injections are given to the mother during labour or to the baby shortly after birth.

This page was last updated on 2015-06-19