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Group A streptococci

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Strep. pyogenes is the only member of Lancefield group A streps. It is the most pathogenic species and is present as a commensal in the throat of less than 10% of people, mostly children. It produces a large number of powerful enzymes and toxins.

Mode of transmission is variable - airborne droplets in urinary tract infections; skin squames or direct contact with lesion as in impetigo.

Group A streptococcus (GAS) is a bacterium which can colonise the throat, skin and anogenital tract. It can cause a diverse range of clinical presentations such as skin, soft tissue and respiratory tract infections, including (1):

  • tonsillitis
  • pharyngitis
  • scarlet fever
  • impetigo
  • erysipelas
  • cellulitis
  • pneumonia

Invasive group A streptococcal disease (iGAS) is defined as an infection associated with the isolation of group A streptococci (GAS) from a normally sterile body site

  • three clinical syndromes are described:
    • (i) group A streptococcal toxic shock syndrome differentiated from other types of iGAS infections by shock and multi-organ system failure early in the course of infection
    • (ii) necrotising fasciitis characterised by extensive local necrosis of subcutaneous soft tissues and skin, and
    • (iii) infections characterised by the isolation of GAS from a normally sterile site in patients not meeting the criteria for streptococcal toxic shock syndrome or necrotising fasciitis
      • included in this group are bacteraemia with no identified focus and focal infections such as meningitis, pneumonia, peritonitis, puerperal sepsis, osteomyelitis, septic arthritis, myositis, and surgical wound infections

Epidemiology of invasive group A strep (2)

  • incidence in 2022 of invasive group A strep in children was reported as (2):
    • 2.3 cases per 100,000 children aged 1 to 4 compared to an average of 0.5 in the pre-pandemic seasons (2017 to 2019)
    • 1.1 cases per 100,000 children aged 5 to 9 compared to the pre-pandemic average of 0.3 (2017 to 2019)
  • deaths within 7 days of an iGAS diagnosis in children under 10 in England
    • 4 deaths in children under 10 during the high season for Group A Strep infection (2017 to 2018)

When prescribing oral antibiotics for possible group A streptococcus (1)

  • phenoxymethylpenicillin remains first line due to its high effectiveness, no reported resistance, and narrow spectrum of activity. In the event of non-availability, amoxicillin, macrolides and cefalexin are alternative agents in decreasing preference
  • in non severe-penicillin allergy, macrolides are the option of choice, with cefalexin as an alternative
  • in severe penicillin allergy, macrolides remain the option of choice. Co-trimoxazole is an option in the event of macrolide non-availability and penicillin anaphylaxis. A severe penicillin allergy is when there is a history of allergy to penicillin with effects that are clearly likely to be allergic in nature such as anaphylaxis, respiratory distress, angioedema or urticaria
  • both cefalexin and co-trimoxazole are broad-spectrum agents that may promote the development of antimicrobial resistance. Resistance to macrolides and co-trimoxazole is currently 7% and 10% respectively
  • antibiotic treatment length for sore throat
    • for phenoxymethylpenicillin:
      • five days of phenoxymethylpenicillin may be enough for symptomatic cure, but a 10-day course may increase the chance of microbiological cure

Management of contacts of GAS (1)

  • contacts will be identified by HPTs (Health Protection Teams)
    • HPTs will advise on who requires prophylaxis. For information, the following individuals who are close contacts of cases are recommended for antibiotic prophylaxis due to higher risk of severe outcomes:
      • pregnant women from >= 37 weeks gestation
      • neonates and women within the first 28 days of delivery
      • older household contacts (>=75 years)
      • individuals who develop chickenpox with active lesions either seven days prior to onset in the iGAS case or within 48 hours after the iGAS case commences antibiotics, if exposure is ongoing
    • close contact is defined as:
      • prolonged contact with the case in a household-type setting during the 7 days before onset of symptoms and up to 24 hours after initiation of appropriate antimicrobial therapy in the index case


  • NHS England. Group A streptococcus communications to clinicians (December 2022).
  • UK Health Security Agency (UKHSA) (December 2nd 2022). UKHSA update on scarlet fever and invasive Group A strep.

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