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Group A Streptococcal Disease, invasive

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Reporting Obligations

Individuals who have or may have Invasive Group A Streptococcal disease shall be reported by phone to the local Health Unit.

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Aetiologic Agent

Invasive Group A Streptococcal (iGAS) disease is caused by the gram-positive B-hemolytic bacterium, Streptococcus pyogenes (S. pyogenes). More than 100 distinct M-protein serotypes of S. pyogenes have been identified.

Clinical Presentation

iGAS infection occurs when the bacteria enter sterile parts of the body such as blood, deep tissue or the lining of the brain. The most common clinical presentations are skin or soft tissue infections, bacteremia with no septic focus, pneumonia, streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis (NF).

S. pyogenes may colonize the throat of individuals (carriers) without symptoms and may be passed from person to person.

Symptoms preceding the onset of invasive GAS disease may be variable and include pain of unusual severity, swelling, fever, chills, influenza-like symptoms, generalized muscle aches, generalized macular rash, bullae, nausea, vomiting, diarrhea, malaise or joint pain.

Symptoms of STSS include the primary site of GAS and or NF, plus hypotension, adult respiratory distress syndrome, renal impairment, rapid onset of shock and multi-organ failure. STSS has a case fatality rate of up to 81%.

For both NF and STSS, rapid diagnosis, aggressive management, and early use of appropriate antibiotics are critical.

Modes of Transmission

Transmission is generally person to person most commonly by:

  • Droplet spread; direct or indirect contact of the oral or nasal mucus membranes or non-intact skin with infectious respiratory secretions or with exudates from wounds or skin lesions; sharing of contaminated needles

Incubation Period

Usually 1–3 days, for pharyngitis; estimated 7–10 days for impetigo. Incubation period for STSS is not known but has been as short as 14 hours in cases associated with subcutaneous inoculation of organisms (e.g., childbirth, penetrating trauma).

Period of Communicability

In untreated uncomplicated impetigo cases, 10–21 days; in untreated conditions with purulent discharges, weeks or months. With adequate treatment, transmissibility generally ends within 24 hours. Persons with untreated streptococcal pharyngitis may carry the organism for weeks or months, but infectivity decreases in 2–3 weeks after onset of infection.

Risk Factors/Susceptibility

The risk of iGAS disease is associated with several underlying conditions including, HIV infection, cancer, heart disease, diabetes, lung disease and alcohol abuse. Other individuals also at increased risk are those with skin breakdown (e.g., burns, wounds, chickenpox), people who use injection drugs and postpartum and postsurgical patients, and children less than one year and adults over 60 years old.

Immunity only develops against the specific M type of GAS and may last for years.

Diagnosis and Laboratory Testing

Isolation of Group A Streptococcus (Streptococcus pyogenes) or deoxyribonucleic acid (DNA) detection by nucleic acid amplification test (NAAT) from a normally sterile site (e.g., blood, cerebrospinal fluid) with or without evidence of clinical severity, OR

Isolation of Group A Streptococcus from a non-sterile site (e.g., skin) with evidence of severity.

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Treatment and Case Management

Treatment is under the direction of the attending health care provider. Prompt identification and aggressive treatment of GAS infections is recommended to prevent increased incidence of invasive GAS disease.

Routine infection prevention and control practices, as well as contact and droplet precautions should be in effect until 24 hours after appropriate treatment is started.

Individuals with confirmed streptococcal pharyngitis, especially school aged children should remain at home until at least 24 hours after beginning appropriate antimicrobial therapy.

All close contacts of invasive GAS disease should be informed about the signs and symptoms of GAS infection and be advised to seek medical attention if signs and symptoms develop within 30 days after exposure to a case.

Chemoprophylaxis is recommended for close contacts of a case of invasive disease with evidence of severity such as in Streptococcal Toxic Shock syndrome, soft tissue necrosis, meningitis, pneumonia or death. All close contacts will be notified by Public Health staff.

For close contacts and chemoprophylaxis recommendations, see PHAC Canada Communicable Disease Report supplement Guidelines for the Prevention and Control of Invasive Group A Streptococcal Disease, or as current.

Patient Information

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Additional Resources

PHAC Canada Communicable Disease Report supplement. “Guidelines for the Prevention and Control of Invasive Group AStreptococcal Disease, or as current.”

Ontario Hospital Association. “Group A Strep (GAS) Disease Surveillance Protocol for Ontario Hospitals.”

Heymann, D.L. Control of Communicable Disease Manual (19th Ed.). Washington, American Public Health Association, 2008


Ministry of Health and Long-Term Care, Infectious Diseases Protocol, 2022.