Invasive Group A Streptococcal infections


  • Recent (2012) increase in Ireland
  • Predominant circulating type - 21/37 (emm/M-type 1)

Clinical presentation

  • Toxic shock (24%) of whom 1/3 died
  • Necrotising facsiitis

What are iGAS infections?

Invasive Group A streptococcal (iGAS) infections are:

  • acute, frequently life-threatening, infections
  • Range from bacteraemia, cellulitis, pneumonia
  • Also meningitis, puerperal sepsis and septic arthritis
  • Less commonly, necrotising fasciitis and Streptococcal Toxic Shock Syndrome (STSS)

STSS characterised

  • Hypotension (<90mmHg in adults) and ≥2 of:
  • Renal impairment (creat x2 normal)
  • Coagulopathy (platelets <100,000x106/l or DIC)
  • Liver dysfunction (ALT, AST or bilirubin x2 normal)
  • ARDS (pulmonary infiltrates & ↓PaO2 without cardiac failure or generalised oedema)
  • Generalised erythematous rash (may desquamate)
  • Soft tissue necrosis (necrotising fasciitis, myositis, gangrene)

More about TSS

Typing and other exciting lab stuff!

Typing of Group A streptococci is primarily based on sequencing the emm gene, which encodes the M protein (a virulence factor found in the bacterial cell wall).

STSS is predominantly associated with emm types 1 and 3 that produce pyrogenic exotoxin A, exotoxin B, or both. These two emm types are commonly associated with outbreaks and increased mortality.


Prompt diagnosis and treatment are essential to reduce the morbidity and mortality associated with iGAS infections.

Early aggressive shock management. early antibiotics

Early senior (EM consultant) and ID/Microbiology involvement.

Suspected severe iGAS ( e.g. STSS, NF, myonecrosis):

  • IV benzyl penicillin 2.4 grams every 4 hours PLUS
  • IV clindamycin 600-900mg TDS PLUS
  • IV flucloxacillin 2g QDS

For other less severe cases (e.g. Post-partum infection):

  • IV benzyl penicillin 1.2-2.4 grams every 4 - 6 hours PLUS
  • IV gentamicin standard dose 5mg/Kg

(For paediatric doses refer to the British National Formulary for Children (BNFc), the Royal College of Paediatrics and Child Health “Medicines for Children” and/or Appendix 5)

When a mother develops peripartum iGAS infection, the infant should have a full diagnostic evaluation and a minimum of 10 days intravenous benzylpenicillin. Gentamicin may be added until blood cultures are sterile and the infant is clinically well. Clindamycin may also be added, if severe iGAS affecting the skin or soft tissues.

Routine chemoprophylaxis of close contacts of iGAS cases is not recommended.

However, close contacts should be informed of the symptoms of iGAS infection, and seek immediate medical care if these occur – HPSC patient information leaflet

Close contacts who develop symptoms or signs consistent with a non-invasive Group A streptococcal infection (e.g. pharyngitis) within 30 days of contact with an iGAS case should receive antibiotic chemoprophylaxis (oral penicillin for 10 days is the treatment of choice).

Antibiotic chemoprophylaxis should also be given to mother and baby, if either develop iGAS within 28 days after the baby’s birth.

Content by Dr Íomhar O' Sullivan following National Alert Dr Fidelma Fitzpatrick (MCRN 17361), Health Protection Surveillance Centre, Dublin, Ireland June 2012.. Last review Dr ÍOS 4/01/22.