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 (NF)

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 q4h
  • PLUS
  • IV clindamycin 600-900mg q8h
  • PLUS
  • IV flucloxacillin 2g q6h

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

  • IV benzyl penicillin 1.2-2.4 grams q4-6h
  • PLUS
  • IV gentamicin 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.

Contact prophylaxis

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 as below.

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

Chemoprophylaxis for iGAS contact
Group Drug Dose Duration
1st line
≥18yrs Amoxicillin 500mg PO q8h 10 days
2nd line (penicillin allergy)
Adults, non-pregannt ♀ Clarithromycin 250 mg PO q12h 10 days
Pregnant & mothers within 28 days of giving birth Erythromycin 500mg PO q6h 10 days
Child 1st line
1 to 11 months Amoxicillin 125mg PO q8h 10 days
1 to 4 years Amoxicillin 250mg PO q8h 10 days
5 to 17 years Amoxicillin 500mg PO q8h 10 days
Child 2nd line (penicillin allergy)
Birth to 6 months Clarithromycin 7.5 mg/kg PO q12h 10 days
6 mo to 17 yrs Clarithromycin 7.5 mg/kg PO q12h (max 250mg every 12 hrs 10 days
< 18yrs who are pregnant or within 28 days of giving birth Erythromycin As per pregnant women dosing above – if very low body weight, consider lower dose and consult a pharmacist 10 days

Content by Dr Íomhar O' Sullivan following National Alert Dr Fidelma Fitzpatrick (MCRN 17361), Health Protection Surveillance Centre, Dublin, Ireland . Last review Dr ÍOS 19/05/23.