Group A Streptococcus

NCCID Disease Debriefs provide Canadian public health practitioners and clinicians with up-to-date reviews of essential information on prominent infectious diseases for Canadian public health practice. While not a formal literature review, information is gathered from key sources including the Public Health Agency of Canada (PHAC), the USA Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO) and peer reviewed literature.

This debrief was prepared by Aleksandra K. Wierzbowski.  Questions, comments and suggestions regarding this debrief are most welcome and can be sent to

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What are important characteristics of Group A Streptococcus?


Group A streptococcus (GAS) bacteria is a Gram positive, beta-hemolytic coccus in chains.   It is responsible for a range of diseases in humans.  These diseases include strep throat (acute pharyngitis) and skin and soft tissue infections such impetigo and cellulitis. These can also include rare cases of invasive (serious) illnesses such as necrotizing fasciitis (flesh eating disease) and toxic shock syndrome (TSS).   Several virulence factors contribute to the pathogenesis of GAS, such as M protein, hemolysins, and extracellular enzymes.

CDC- Group A Streptococcal Disease – For Clinicians
PHAC- Pathogen Safety Data Sheet- Streptococcus pyogenes (Group A Strep)


Signs and symptoms of GAS infections will vary based on the disease the infection causes.

Strep throat

Symptoms may include a swollen red sore throat and tonsil (pharyngeal and tonsillar erythema), tonsillar hypertrophy with or without exudates, palatal petechiae (uncommon but highly specific finding), high fever, headache, and swollen lymph nodes in the neck (anterior cervical lymphadenopathy).  Abdominal pain, nausea, and vomiting might be present especially among children.

Cough, rhinorrhea, hoarseness, oral ulcers, and conjunctivitis are not typically seen in patients with group A strep pharyngitis and are therefore strongly suggestive of a viral etiology.

CDC-Group A Streptococcal Disease – For Clinicians  
CDC-Group A Streptococcal Disease-Pharyngitis
Mayo Clinic- Strep Throat – written for patients and the general public

Scarlet fever

Infected individuals may experience a quickly spreading red rash (erythematous rash that blanches on pressure) that feels like sandpaper on the body. The rush begins on the trunk, then spreads outward, usually sparing the palms, soles, and face but accentuates in flexor creases (i.e., under the arm, in the groin), termed “Pastia’s lines”.  They may also have red swollen lips and red spots on the tongue (red papillae). Circumoral pallor and strawberry tongue may be present as the disease resolves.

Scarlett fever usually occurs with acute pharyngitis although it can also follow group A strep pyoderma or wound infections.

CDC-Group A Streptococcal Disease – For Clinicians 
CDC-Group A Streptococcal Disease – Scarlet Fever
Mayo Clinic- Scarlet Fever – written for patients and the general public


Symptoms may include a red skin rash that looks like a group of small blisters or red bumps. When the blisters burst and fluid seeps out, the fluid dries and the blisters become coated with a yellow or grey crust. The sores usually occur around the nose and mouth but can be spread to other areas of the body by fingers, clothing and towels. Itching and soreness are generally mild.

A less common form of the disorder, called bullous impetigo, may feature larger blisters that occur on the trunk of infants and young children. A more serious form of impetigo, called ecthyma, penetrates deeper into the skin — causing painful fluid- or pus-filled sores that turn into deep ulcers.

Mayo Clinic- Impetigo  – written for patients and the general public

Invasive Group A Streptococcus Infections

May present as any of several clinical syndromes, including pneumonia, bacteremia in association with cutaneous infection (e.g., cellulitis, erysipelas, or infection of a surgical or non-surgical wound), deep soft tissue infection (e.g., myositis or necrotizing fasciitis), meningitis, peritonitis, osteomyelitis, septic arthritis, postpartum sepsis (i.e., puerperal fever), neonatal sepsis, STSS or nonfocal bacteremia.  Skin and soft tissue infections tend to be the most common invasive GAS manifestations.

Toxic shock syndrome 

Streptococcal TSS results in a rapid drop in blood pressure and organ failure. Symptoms may include fever, redness of the skin, dizziness, influenza-like symptoms, confusion, shock, diarrhoea, vomiting and severe muscle pain. This disease is the most serious manifestation of invasive GAS disease.

Mayo Clinic- Toxic Shock Syndrome – written for patients and the general public

Necrotizing Fasciitis (NF) with or without Necrotizing Myositis (NM) is present in about 50 per cent of patients with STSS.

Necrotizing Fasciitis (sometimes called “the flesh-eating bacteria”):

NF is a deep-seated infection of the subcutaneous tissue that results in rapid destruction of fascia and fat, but may spare the skin itself.  Symptoms may include fever and intense pain, redness and swelling in the affected area. Often the pain is disproportionate to (much worse than) the appearance of the infection.

Necrotizing Myositis occurs in patients with NF and STSS.


The group A streptococcal infections can range from mild and uncomplicated such as acute GAS pharyngitis to life threating invasive GAS infections such as STSS.

PHAC- Pathogen Safety Data Sheet- Streptococcus pyogenes (Group A Strep)

There are Pus-Forming (Suppurative) Complications and inflammatory (nonsupprative) complications of untreated Group A Streptococcal infections such as Strep Throat Strep or scarlet fever.


The 3 most common pus-forming complications that can occur from untreated strep throat include: peritonsillar or retropharyngeal abscess, otitis media, and sinusitis.  Other less common complications that result from the formation of pus include infections that spread to the blood, spinal cord, brain, and muscle sheaths. These complications can also be life-threatening if not treated appropriately.


Post-Streptococcal Glomerulonephritis: is a kidney disease that can develop as a result of the immune system fighting off the group A strep throat or skin such as strep throat, scarlet fever, and impetigo. It usually takes about 10 days after strep throat or scarlet fever and about 3 weeks after a group A strep skin infection for PSGN to develop.

Symptoms of PSGN can include: dark, reddish-brown urine, swelling (edema), especially in the face, around the eyes, and in the hands and feet, decreased need to pee or decreased amount of urine, feeling tired due to low iron levels in the blood (fatigue due to mild anemia). In addition, someone with PSGN usually has protein in the urine and high blood pressure (hypertension).

Some people may have no symptoms or symptoms that are so mild that they don’t seek medical help.

CDC-Group A Streptococcal Diseases – Post-Streptococcal Glomerulonephritis
CDC – Complications – Post- Streptococcal Glomerulonephritis – For Clinicians

Rheumatic fever:  is an inflammatory disease that can develop as a complication of inadequately treated strep throat or scarlet fever. Rheumatic fever can cause permanent damage to the heart, including damaged heart valves and heart failure.  Rheumatic fever symptoms vary ranging from few symptoms or several, and symptoms do not all appear simultaneously and can change during the course of the disease. The onset of rheumatic fever usually occurs about two to four weeks after a strep throat infection.

The signs and symptoms of rheumatic fever (inflammation in the heart, joints, skin or central nervous system) can include:

Fever; painful, red, hot, swollen and tender joints – most often in the knees, ankles, elbows and wrists, pain might migrate from one joint to another; small, painless bumps (nodules) beneath the skin, flat or slightly raised, painless rash with a ragged edge (erythema marginatum), chest pain, heart murmur, fatigue; jerky, uncontrollable body movements (Sydenham chorea, or St. Vitus’ dance) – most often in the hands, feet and face,  outbursts of unusual behavior, such as crying or inappropriate laughing, that accompanies Sydenham chorea.

The link between strep infection and rheumatic fever isn’t clear, but it appears that the bacterium tricks the immune system (molecular mimicry).

Mayo Clinic- Complications- Rheumatic Fever – written for patients and the general public


The incubation period of group A strep infections is approximately 2 to 5 days.

PHAC- Pathogen Safety Data Sheet- Streptococcus pyogenes (Group A Strep)
CDC- Group A Streptococcal Disease – For Clinicians


Human noses, throat and skin are the primary reservoirs for GAS and the bacteria is often carried without symptoms. These carriers are less contagious than symptomatic carriers of the bacteria. Infections in children are an important reservoir for infections in adults.

Transmission of GAS is through the air via respiratory droplets, such as coughs, sneezes, and nasal secretions.  GAS can also spread from person to person through close contact such as kissing, sharing drinking cups, forks, spoons or cigarettes.

Crowded conditions — such as those in schools, daycare centers, or military training facilities — facilitate transmission.

Although rare, spread of group A strep infections may also occur via food. Foodborne outbreaks of group A strep have occurred due to improper food handling.

The portal of entry for invasive GAS infections is often the skin or soft tissue and infection may follow minor or unrecognized trauma without an obvious break in the skin.

CDC-Group A Streptococcal Disease- For Clinicians


The diagnosis of group A strep infections (pharyngitis) is confirmed by either a rapid antigen detection test (RADT) or a throat culture. The diagnosis of invasive GAS is based on the culture of GAS organisms from specimens taken from normally sterile body site.

In the case of NF a non-sterile wound sample might be taken.

RADTs have high specificity for group A strep but varying sensitivities when compared to throat culture. Throat culture is the gold standard diagnostic test. A negative RADT in a child with symptoms of scarlet fever should be followed up by a throat culture.

CDC-Group A Streptococcal (GAS) Disease – For Laboratorians


GAS spreads by contact with infected respiratory droplets or contact with items that might be contaminated with the saliva of an infected person. Measures that reduce the risk of transmission include:

  • Good hand hygiene – wash hands often with soap and water, or use alcohol hand rub.
  • Avoid sharing items that could be contaminated with saliva such as water bottles, drinking glasses, utensils, etc.
  • Clean and disinfect high touch/potentially-contaminated surfaces.
  • Cover coughs or sneezes with a tissue or a forearm.
  • Stay home from work, school, or daycare until afebrile and until 24 hours after starting appropriate antibiotic therapy
  • Employ harm reduction strategies among injection drug user population

The use of a recommended antibiotic regimen to treat group A streptococcus infections shortens the duration of symptoms; reduces the likelihood of transmission to family members, classmates, and other close contacts; and prevents the development of complications, including acute rheumatic fever.

PHAC-CCCR-Guidelines for the Prevention and Control of Invasive Group A Streptococcus
PHAC- Pathogen Safety Data Sheet- Streptococcus pyogenes (Group A Strep)


There is currently no vaccine to prevent group A strep infections, although several vaccines are in development.

CDC-Group A Strep Disease Outbreak Response


Most people who are exposed to someone with a group A strep infection should not receive prophylaxis. However, in some situations, prophylaxis may be recommended for someone who is exposed to someone with an invasive group A strep infection (i.e., necrotizing fasciitis, streptococcal toxic shock syndrome).

CDC-Group A Strep Disease Outbreak Response
PHAC-Recommendations for Chemoprophylaxis ARCHIVED AND IS NOT BEING UPDATED


Treatment will vary based on the disease a person has. Some diseases, such as strep throat, can heal on their own. Others, such as impetigo, may require the use of antibiotics to heal.

Untreated streptococcal pharyngitis usually resolves within a few days. Treatment with antibiotics shortens the duration of the acute illness by about 16 hours. The primary reason for treatment with antibiotics is to reduce the risk of complications such as rheumatic fever and retropharyngeal abscesses; antibiotics are effective if given within 9 days of the onset of symptoms.

For invasive GAS infections, antibiotics, hospitalization and surgery may be required. Surgery is almost always required for necrotising fasciitis.

Penicillin or amoxicillin is the antibiotic of choice. There has never been a report of a clinical isolate of group A strep that is resistant to penicillin. For patients with a penicillin allergy, recommended regimens include narrow-spectrum cephalosporins (e.g., cephalexin, cefadroxil), clindamycin, azithromycin, and clarithromycin.

CDC- Group A Strep Disease- Treatment



Different clinical manifestations of this bacterium are more common in different parts of the world. Streptococccal pharyngitis is predominant in temperate areas and peaks in late winter and early spring. Impetigo is more common in warm humid climates.  School-aged children carry S. pyogenes in their throats and are more at risk of having the disease.

PHAC- Pathogen Safety Data Sheets: Infectious Substances – Streptococcus pyogenes


Invasive GAS disease became nationally notifiable in January 2000. The most recent year for which complete national data have been published is 2001. The overall incidence of disease in 2001 was 2.7 per 100,000 population. The highest reported incidence rates occurred among adults 60 years of age (5.3 per 100,000), followed by children < 1 year of age (4.8 per 100,000) and children 1 to 4 years of age (3.6 per 100,000). Elevated rates of invasive GAS disease have been detected among Indigenous populations living in the Canadian Arctic through the population-based International Circumpolar Surveillance system. Between 2000 and 2002, no cases of invasive GAS disease were reported among non-Indigenous persons in the territories, northern Quebec or northern Labrador. In contrast, among Indigenous people living in northern Canada, the incidence rate of disease was 9.0 per 100,000 in 2000 (7 cases), 3.0 per 100,000 in 2001 (2 cases) and 5.0 per 100,000 in 2002 (4 cases).

PHAC-Epidemiology of Invasive GAS Disease in Canada


CDC-Surveillance reports
CDC-ABCs Report: Group A Streptococcus, 2015Back to top

What is happening with current outbreaks of Group A Streptococcus?

Middlesex-London Health Unit, ON has issued an Invasive Group A Streptococcal (iGAS) Disease Outbreak Alert on Nov. 27, 2017.

Although nearly half of the cases have been among intravenous drug users or those without stable housing, officials with the Middlesex-London Health Unit have noticed an increase in infections among patients not connected to that group.

Middlesex-London Health Unit- Group A Streptococcal Disease including a fact sheet developed by the Middlesex-London Health Unit:
Huffington Post- Streptococcus Outbreak in London, Ontario, Kills 9
CBC News- What you need to know about the Streptococcus outbreak in London, Ontario
The Globe and Mail – ‘A very wily opponent’: New findings bring scientists closer to defeating group A strep
The Globe and Mail- Streptococcus outbreak in Canada is part of a larger storyBack to top

What is the current risk for Canadians from GAS?

There are some factors which can increase the risk for Group A Strep Infection (strep throat).  Young age is one of them. Children are at highest risk of getting strep throat. Time of the year.  The risk for GAS infection is perennial but mostly it can happen in early spring and late fall.

Although healthy people can get a severe infection from GAS, there are some factors that might put Canadians at higher risk of developing invasive GAS and these include:

  • Those who are over the age of 65 years and very young children
  • People who have weakened immune systems, such as those who are on immunosuppressive therapy, or have HIV infection
  • People with chronic diseases, such as diabetes, heart or lung disease, or cancer
  • People who use injection drugs
  • People who abuse alcohol
  • People with chronic skin breaks and lesions, including children with chickenpox

What measures should be taken for a suspected Group A Streptococcus case or contact?

Case and contact management, case definitions and identification and reporting have been established for notifiable, invasive Group A Streptococcus infections.


The public health response to a sporadic case of invasive GAS disease includes management of the case, contact identification and tracing, and maintenance of surveillance for further cases.

The management of invasive GAS disease is divided into four subsections: the management of cases, contact management, management of cases occurring at long term care facilities and management of cases occurring among children attending child care centres.

PHAC- Pathogen Safety Data Sheet- Streptococcus pyogenes (Group A Strep)


Laboratory confirmation of infection with or without clinical evidence of invasive disease is considered a confirmed case.  Laboratory confirmation requires the isolation of group A streptococcus (Streptococcus pyogenes) from a normally sterile site.

PHAC- Pathogen Safety Data Sheet- Streptococcus pyogenes (Group A Strep)


In Canada, confirmed cases of invasive GAS disease are notifiable at the national level. Invasive GAS disease became nationally notifiable in January 2000. Probable cases of invasive GAS disease are not nationally notifiable.

Invasive Group A Streptococcus Reporting by laboratories is only required for GAS isolated from sterile sites as defined under provincial guidelines.

PHAC- Invasive GAS- Surveillance and Reporting ARCHIVED AND IS NOT BEING UPDATED
PHAC- Pathogen Safety Data Sheet- Streptococcus pyogenes (Group A Strep)


Infection Control for Invasive Group A Streptococcus Infection in Hospitals have been developed.

PHAC- Infection Control for Invasive Group A Streptococcus Infection in Hospitals ARCHIVED AND IS NOT BEING UPDATED
PHAC- Pathogen Safety Data Sheet- Streptococcus pyogenes (Group A Strep)