Group A Streptococcal Infections: What to Know

Medically Reviewed by Dan Brennan, MD on April 17, 2023
6 min read

If you’ve had a sore throat from time to time or blisters around your mouth or nose, chances are you’ve had a group A streptococcal (GAS) infection. Group A streptococcus is the bacteria that causes these infections and illnesses, especially on the skin and throat. Doctors commonly call it “strep A.”

There are more than 120 strains of bacteria that cause GAS infections. They spread easily but are mostly mild and easy to treat. Some people carry GAS and don’t even get sick. Certain strains of bacteria can cause infections that are life-threatening, especially if they’re not treated. 

You’re most likely to catch the infection when the streptococcal A bacteria enters your body through direct contact with a person who has symptoms of a strep A infection. This could happen when they sneeze or cough. Or you might get it if you come into direct contact with an infected sore on their skin. 

After you’re exposed to streptococcal bacteria, it is usually 2 to 5 days before symptoms start. 

If you have the GAS bacteria but don’t get ill, you’re less likely to spread the bacteria. 

Anybody can get group A strep infections. In fact, about 10 million people get mild versions of group A strep each year. But children in certain age groups are more prone to getting them:

  • Children 5-15 are more likely to get strep throat or scarlet fever. 
  • Kids 2-5 more commonly get skin infections like impetigo. This might be because little kids touch surfaces and other things, then often put their hands near their mouth or nose.

Infections can range from mild to serious, even life-threatening. But most are mild and usually go away with basic treatment. 

Mild group A strep infections: 

  • Sore throat. Symptoms include pain or other discomfort, like scratchiness. 
  • Strep throat. This affects your throat and tonsils. Your throat may look red, and it might hurt to swallow. 
  • Cellulitis. The bacteria get deep into tissue below your skin. The infection causes the skin to swell and look red and inflamed. It might be painful or warm to touch. This usually happens on your arms and legs. But it can also happen around your eyes, mouth, belly, and anus.
  • Erysipelas. This infection affects the top layers of skin, often on your face or legs. It causes hard, very red patches that are painful. You could also have fever and chills.
  • Impetigo. This causes sores and blisters around your mouth and nose, or your arms and legs.

Serious group A strep infections:

  • Scarlet fever. This causes a rash, a high fever, and sore throat. It often affects children. Your throat may be very red, and glands in your neck could be swollen. You might have a headache or body aches, and maybe nausea and vomiting.
  • Bacteremia. This happens when bacteria get into your bloodstream. It could cause you to get other conditions, including endocarditis (inflammation in the heart). 
  • Rheumatic fever. This infection can happen if strep throat, scarlet fever, and strep skin conditions aren’t treated. It causes inflammation and can affect your heart, joints, brain, and skin. 

Invasive group A strep infections: 

Sometimes, bacteria can go to parts of your body where they usually don’t spread, including deep muscle and fat tissue, your blood, or your lungs. 

You’ll need medical attention as soon as possible with aggressive treatment to control the infection. 

Two rare, but severe types of invasive group A strep infections include:

  • Necrotizing fasciitis. You may have heard this condition called “flesh-eating bacteria.” The infection destroys muscle and fat tissue. It doesn’t spread very easily from person to person.

    You can get the infection if you have a break in your skin such as from cuts, wounds, or even insect bites. You can also get the infection after surgery. You might be more prone to getting it if your immunity is low; for example, if you have diabetes or cancer. Once the bacteria enter your body, they can spread quickly.

    Early symptoms can include red, warm, swollen skin that’s very painful. You might also have a fever. Once the bacteria start to spread, you might notice black spots around the infected area, changes in the color of the skin, pus and blisters on the skin, diarrhea, and dizziness.

    Even with treatment, about 1 in 5 people with necrotizing fasciitis die from the infection. If you see these signs of flesh-eating bacteria, call 911 and get medical help right away. 

  • Streptococcal toxic shock syndrome. This rare bacterial infection is not very contagious but spreads very quickly when it gets into the body.

    Symptoms usually start out as fever, chills, nausea, vomiting, and muscle aches. But as it spreads over a day or two, it can cause low blood pressure and shock, plus damage to organs including your kidneys, liver, and lungs. If you don’t get timely medical help, it can lead to multiple organ failure and even death.

    About 6 in 10 people who get this group A strep infection die from complications. 

Anybody can get invasive group A strep infections. But people who have chronic illnesses like cancer, diabetes, and kidney failure are more likely to get them. And streptococcal toxic shock syndrome is most common in people who are 65 and older.

The CDC says there are about 10,000 to 15,000 cases of invasive group A strep infections each year. Of those, about 1,500 cases are necrotizing fasciitis infections and as many as 3,000 are streptococcal toxic shock syndrome infections. 

If you think you have a bacterial infection, go to a doctor as soon as possible. They’ll do a detailed physical exam, ask you questions about your medical history and symptoms, and do some tests.

To confirm a diagnosis, they might:

  • Run a blood test to look for infection
  • Take swabs of your throat or infected skin and run lab tests
  • Take a biopsy (a small piece of tissue) to check it under a microscope
  • Do imaging tests like an MRI, a CT scan, or an ultrasound to look for infection underneath your skin

If you have a bacterial infection caused by a strain of group A strep, your doctor will prescribe antibiotics to treat it. 

Depending on the type of infection you have, the antibiotic could come in the form of a pill you take by mouth, a liquid, or an ointment you put on infected skin. In serious cases, you might need to get antibiotics injected or get them through an IV.

The antibiotics can help ease the symptoms, shorten the infection period, and stop the infection from spreading or causing serious complications. Usually, you’ll start to feel better about 3-5 days after you start treatment. But more serious infections could take up to 2 weeks to clear up. 

It’s important to use antibiotics exactly as your doctor tells you. Follow the instructions closely, and don’t skip or stop taking the medication. If you do miss a dose, don’t double up. And if you do have to stop it because of side effects, check with your doctor first. This can help you avoid antibiotic drug resistance in the future. 

For invasive group A strep infections, you’ll need medical attention at a hospital or emergency room as soon as you notice symptoms. For necrotizing fasciitis and toxic shock syndrome, you might need surgery along with antibiotics to remove infected skin or tissue to prevent the spread. 

To lower your odds of getting – or spreading – group A strep infections:

  • Wash your hands often with soap and water.
  • Keep any open cuts, skin wounds, sores, and blisters clean and covered until they heal.
  • Cover your mouth and nose when you cough or sneeze. And throw away used tissues.
  • Don’t share utensils or food with someone who is sick or shows symptoms of infection.
  • Stay home and rest if you’re feeling sick.