It's probably just a run-of-the-mill case of strep, that soreness that's gripping your throat. After all, group A streptococcus (GAS) is a bacterium that many of us carry around without any ill effects.

If we do feel anything, chances are we'll be hit by a mild case of strep throat or the skin condition impetigo.

The U.S. Centers for Disease Control and Prevention estimates GAS causes between 20 and 30 per cent of sore throats in children and five to 15 per cent of sore throats in adults. 

But sometimes the effects can be far nastier. If the bacteria get into parts of the body where bacteria usually are not found — like blood, muscle and the lungs — the results can be devastating. Even fatal.

Two of the most serious illnesses caused by GAS infection are streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis, or flesh-eating disease.

Streptococcal toxic shock syndrome will cause your blood pressure to drop rapidly and organs like your kidneys, liver or lungs to fail after the immune system overreacts

Necrotizing fasciitis is a fast-spreading infection that works its way rapidly through the layers of tissue (the fascia) that surrounds muscles.

About 20 to 30 per cent of cases of these illnesses are fatal.

Health Canada has reported more than 1,400 cases of invasive group A strep per year between 2010 and 2014, the most recent period for which data is available. 

Infectious disease specialists estimate that in one in a million cases, strep A can lead to toxic shock

Most recently, Toronto doctors had to amputate an arm and a leg of an 11-year-old girl to manage the complication.

Between 2005 and 2009, researchers in western Canada reported a large outbreak of invasive pneumococcal disease caused by a severe strain that moved east across the country. 

What are the early symptoms of streptococcal toxic shock syndrome and necrotizing fasciitis?

The early signs and symptoms of STSS include:

  • Fever.
  • Abrupt onset of generalized or localized severe pain, often in an arm or leg.
  • Dizziness.
  • Flu-like symptoms.
  • Confusion.
  • A flat red rash over large parts of the body, in about 10 per cent of cases.

In the early stages of necrotizing fasciitis, you may experience:

  • Severe pain and swelling.
  • Fever.
  • Redness at the site of a wound.

For both illnesses, the infection sometimes starts at the site of a minor injury, such as a cut or bruise, but sometimes there is no obvious source of infection.

What is the risk?

Scientists don't know why streptococcus bacteria causes only minor infections in some people but poses a serious threat to others.

According to Health Canada, some of the risk factors that have been identified include:

  • A weakened immune system, which could be caused by such factors as disease (HIV infection, AIDS), cancer treatments (radiation and chemotherapy) or by anti-rejection drugs taken following a bone marrow or organ transplant.
  • Chronic diseases, including heart, lung and liver disease.
  • Recent close contact with someone who has flesh-eating disease that was caused by group A streptococcus (GAS) bacteria.
  • Chickenpox infection. (It should be noted that while flesh-eating disease can be a complication of chickenpox in children, such occurrences are very rare.)

Should you be concerned about more serious illnesses if you contract strep throat?

No. Millions of people in North America get strep throat every year, but less than one in a million will actually develop flesh-eating disease or streptococcal toxic shock syndrome. The vast majority of group A streptococcal cases arise from skin and soft tissue disease, not from strep throat.

How is invasive group A streptococcal disease treated?

Because the necrotizing fasciitis progresses so rapidly (the infection destroys tissue so quickly that it can cause death within 12 to 24 hours), treatment usually involves antibiotics to fight the infection and surgery to remove the infected tissue. There is no vaccine to prevent flesh-eating disease.

High doses of penicillin and clindamycin are used to treat both necrotizing fasciitis and STSS.

The key is to start treatment as early as possible.