Case Definition for Invasive Group A Streptococcal Infection (iGAS)

Clinical criteria

Severe clinical presentation consistent with iGAS or severe GAS infection such as;

  • streptococcal toxic shock syndrome (STSS)
  • necrotising fasciitis
  • pneumonia
  • septic arthritis
  • meningitis
  • peritonitis
  • osteomyelitis
  • myositis
  • puerperal sepsis
  • cellulitis

accompanied by a systemic presentation necessitating hospitalisation.

Laboratory criteria

  • Laboratory criteria
    1. Isolation of group A streptococcus (GAS), by culture or molecular methods (such as PCR), from a normally sterile body site (blood, cerebrospinal fluid, pleural-peritoneal-pericardial fluids, joint aspirate, bone, or deep tissue or abscess at operation or post-mortem)
    2. Isolation of GAS from a non-sterile site (e.g. throat, sputum, vagina)

Epidemiological criteria

Suspected case has an epidemiological link to a confirmed case of iGAS

Case classification 

  1. Confirmed case
    1. Any person meeting the laboratory criteria of (1) above


    2. Any person meeting the laboratory criteria of (2) above PLUS the clinical criteria described above

  2. Probable case
    1. Any person meeting the clinical criteria above


      • the epidemiological criteria above


      • the clinician considers that GAS is the most likely cause


Current as of: 22 December 2022