Department of Health

Invasive group A streptococcal disease (iGAS)

iGAS is an urgent notifiable condition. Find out about diagnosis, treatment and control measures

Key messages

  • From 1 March 2024, invasive group A streptococcal disease (iGAS) is an urgent notifiable condition that must be notified by medical practitioners and pathology services immediately upon diagnosis to the Department of Health.
  • iGAS is a severe, invasive disease caused by infection with Streptococcus pyogenes bacterium, also known as Group A Streptococcus.
  • iGAS can have various presentations including bacteraemia/septicaemia, streptococcal toxic shock syndrome and necrotising fasciitis which are associated with high morbidity and mortality.
  • Diagnosis of iGAS relies on the detection of Streptococcus pyogenes from a normally sterile site, or from a normally non-sterile site with supporting clinical evidence of severe, invasive disease.
  • Treatment of iGAS includes urgent antibiotic treatment and often requires intensive care support, surgical debridement, and other supportive therapies.
  • Certain groups who have been exposed to cases of iGAS may be recommended to receive antibiotics for chemoprophylaxis.
  • Primary school and childcare exclusions apply for iGAS.

Notification requirement for iGAS

From 1 March 2024, invasive group A streptococcal disease (iGAS) is an urgent notifiable condition and must be notified by medical practitioners and pathology services immediately to the Department of Health by telephone on 1300 651 160 (24/7) upon diagnosis. Pathology services must follow up with written notifications within 5 days.

This is a Victorian statutory requirement.

Primary school and children's services centres exclusion for iGAS

Children with iGAS must not attend primary school and children’s service centres until they have received antibiotic treatment for at least 24 hours and feel well.

For more information, see Streptococcal infection School exclusion table.

Infectious agent of iGAS

iGAS is caused by Streptococcus pyogenes, also known as Group A Streptococcus (GAS), a Gram positive, ß-haemolytic bacterium.

Identification of iGAS

Clinical features

There are a range of clinical presentations related to GAS infections. These include common mild illnesses such as scarlet fever, tonsilitis or pharyngitis (also known as “strep throat”) and skin or soft tissue infections such as impetigo or cellulitis.

In rare instances, GAS infections can lead to severe, invasive disease in the form of iGAS which is usually defined by the isolation of GAS from a normally sterile site, such as blood, cerebrospinal fluid, or bone marrow.

Presentations of iGAS may include:

  • bacteraemia or septicaemia
  • streptococcal toxic shock syndrome
  • necrotising fasciitis
  • pneumonia or empyema
  • meningitis
  • osteomyelitis or septic arthritis
  • puerperal or post-partum sepsis.

These conditions can be life-threatening or lead to complications and disability such as limb-loss and severe scarring. In high income countries, the mortality rate of iGAS is estimated to be 5-15%, increasing to 30% and above for streptococcal toxic shock syndrome and necrotising fasciitis.


Diagnosis of iGAS relies on laboratory evidence of GAS in appropriate specimens, either from a normally sterile site OR from a normally non-sterile site with supporting clinical evidence of severe, invasive disease. GAS can be isolated by culture or detected by nucleic acid testing.

Diagnosis of iGAS can be made :

a) Evidence of GAS from a normally sterile site, which includes:

  • blood, cerebrospinal fluid, pleural fluid, peritoneal fluid, pericardial fluid, joint fluid, bone, bone marrow
  • internal organs; specimens obtained from surgery or aspirate from one of the following: lymph node, brain, heart, liver, spleen, vitreous fluid, kidney, pancreas, ovary, or vascular tissue.

For notification purposes, this does not include specimens that represent continued spread from related tissue degeneration (such as a deep diabetic ulcer leading to adjacent bone infection) OR lung tissue.

b) Evidence of GAS from a normally non-sterile site, including abscess at procedure, with clinical evidence of iGAS such as in the form of:

  • streptococcal toxic shock syndrome
  • necrotising fasciitis
  • puerperal or post-partum sepsis.

Incubation period of iGAS

The incubation period for iGAS is not well defined.

Cases of iGAS may be preceded by superficial non-invasive GAS infections, such as GAS pharyngitis (incubation period is usually 1 to 3 days) or GAS impetigo (estimated incubation period is 7 to 10 days). Secondary cases of iGAS infection have been identified up to 30 days after the identification of the initial case, though this is rare.

Public health significance and occurrence of iGAS

The overall risk of iGAS in the general population is low. Most people who are exposed to GAS bacterium do not develop iGAS. However, the public health risk of iGAS can be significant as it can lead to death or serious complications. The incidence, morbidity and mortality is highest among certain population groups, such as infants, the elderly, and Aboriginal and Torres Strait Islander peoples.

Since 1 July 2021, iGAS became a nationally notifiable condition. In Victoria, iGAS became notifiable under the Public Health and Wellbeing Regulations 2019 from 1 February 2022. Based on available Victorian surveillance data, rates of iGAS have increased from 3.0 cases per 100,000 population in 2022 to 9.9 cases per 100,000 population in 2023. While rates of iGAS have fluctuated over time, an increase in case numbers was observed from late 2022 across many states and territories that continued into 2023. Similar increases in case numbers were reported during this time in several European countries. The underlying reason for these observed trends remains unclear. Further longitudinal surveillance and high quality data on iGAS is needed to accurately infer epidemiological trends and population impacts.

Seasonality of iGAS in Australia has not been well-established, although some evidence suggests an increase in incidence during periods of increased influenza circulation. Internationally, iGAS trends in high-income countries show seasonal peaks in winter to early spring.

Clusters of iGAS cases may occur in households and institutional settings. In Australia and internationally, outbreaks have been documented in settings such as aged care facilities, hospitals, and childcare facilities, with aged care facilities being the most frequently reported setting of iGAS outbreaks.

Reservoir of GAS bacterium


Mode of transmission of GAS bacterium

GAS bacterium is spread from person-to-person through respiratory droplets, contact with other infectious secretions (such as saliva, wound discharge, or nasal secretions) or skin-to-skin contact.

Period of communicability of iGAS

People with iGAS are considered infectious from 7 days before onset of symptoms until 24 hours after commencement of appropriate antibiotic treatment.

Susceptibility and resistance to iGAS

People at potential risk of secondary iGAS infection following exposure to someone with iGAS include:

  • birthing parent-neonatal pairs
  • household or household-like contacts of a case
  • care and institutional setting contacts (such as residential aged care or disability facility, child-care, hospital, prison, military barracks or etc) contacts.

The risk in healthcare workers who have had unprotected close exposure during airway management (e.g. suctioning, intubation), or mouth to mouth resuscitation is considered low.

There is some evidence to suggest an increased risk of iGAS in the following population groups as well:

  • children aged less than 5 years
  • elderly people, particularly those aged over 75 years
  • Aboriginal and Torres Strait Islander people
  • people with a chronic or immunocompromising disease or condition
  • people who inject drugs
  • people experiencing homelessness
  • people residing at or attending institutions prone to poor hygiene.

Control measures for iGAS

Preventive measures

There is currently no vaccine available to prevent against GAS infections or iGAS.

Early detection and treatment of non-invasive GAS infections such as throat and skin infections may help prevent against the development of severe invasive disease.

Residential and institutional settings may reduce the risk of infections and spread by following infection prevention and control practices and encouraging good hygiene practices in clients, staff and visitors.

Control of case

iGAS is treated with antibiotic treatment and often requires intensive care therapy, surgical debridement, intravenous immunoglobulin treatment and other supportive therapies in a hospital setting. Treatment is the responsibility of the treating doctor. For antibiotic treatment recommendations refer to the current edition of Therapeutic guidelines: antibiotic or an infectious diseases specialist.

People with iGAS should be provided care in standard and droplet transmission-based precautions until they have received treatment with appropriate antibiotics for at least 24 hours.

Control of contacts

People who have been exposed to GAS bacterium from someone with iGAS may be at increased risk of secondary iGAS infection and designated as contacts. Local Public Health Units work with clinicians to identify contacts and advise on public health actions to prevent secondary cases.

Contacts should be notified of their exposure, provided information about iGAS and advised to monitor for symptoms. Eligible contacts who are most at-risk may also be recommended to receive antibiotics for chemoprophylaxis.

For information on iGAS for the general public refer to the Streptococcal infection - group AExternal Link on the Better Health Channel.

Antibiotic chemoprophylaxis for contacts

Based on available research, antibiotics may be used as chemoprophylaxis to help reduce the risk of secondary iGAS infection following infectious exposure in certain higher risk contacts. Recommendations for chemoprophylaxis should be made based on risk assessment that considers the individual’s risk factors to iGAS, context of infectious exposure, and risk of adverse effects.

For further information on antibiotic chemoprophylaxis for iGAS, see the Therapeutic guidelines: antibioticExternal Link or contact an infectious diseases specialist. Some health services may apply internal guidelines for antibiotic chemoprophylaxis in contacts of iGAS cases that are appropriate for their patient population. Local Public Health Units can assist clinicians with the identification and management of contacts

Antibiotics for chemoprophylaxis should be given to eligible contacts as soon as possible, preferably within 48 hours of exposure to the original case or, at least, within 48 hours of the case being notified. The utility of providing chemoprophylaxis beyond 10 days of iGAS diagnosis in the original case is limited.

For further information refer to the Invasive Group A Streptococcal (iGAS) Disease – CDNA National guidelines for Public Health Units | Australian Government Department of Health and Aged CareExternal Link

Control of environment

This is not routinely required for iGAS.

Outbreak measures for iGAS

The Department of Health or Local Public Health Units may identify a cluster or outbreak where two or more linked cases of iGAS occur in the same setting within a defined time period.

Public health actions to control the cluster or outbreak may include:

  • investigation of the infectious exposure
  • infection prevention and control measures to reduce transmission risk
  • contact identification and provision of information about iGAS and recommendations for antibiotic chemoprophylaxis
  • additional laboratory analysis of detected GAS bacterium to check for matching by molecular typing by the public health reference laboratory
  • continued surveillance in the setting to monitor for additional cases
  • communication to clinicians and health services for increased awareness, testing and case finding.

Reviewed 26 February 2024


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