Strep throat is a contagious bacterial infection. The group of bacteria called group A streptococcus (group A strep) causes this infection.

Strep throat can make a person’s throat feel sore and scratchy. Strep throat only accounts for a small number of sore throats and is more common in children than adults. Viral infections, not bacterial, cause most sore throats.

Once a person develops a strep throat infection, they can easily transmit it to others through close contact, shared drinks, food, or contaminated surfaces.

In this article, we examine how people transmit strep throat. We also look at strep throat’s incubation period, how long people remain contagious, and how to prevent transmission.

a doctor examining a man's throat to see if he has strep throat which is contagiousShare on Pinterest
A person with strep throat may transmit it to people they are in close contact with.

Strep throat is highly contagious, especially among people in close contact with someone who has an infection, such as children in school and nursery environments.

A group of bacteria called group A strep cause strep throat. Group A strep also cause some other infections, including:

Group A strep bacteria usually live in the skin and throat without a problem. When the bacteria grow out of control, a person may develop strep throat.

Many infections and illnesses can cause a sore throat, including many that do not respond to antibiotics, such as allergies, viruses, and reflux.

A person who has these symptoms may not necessarily have strep throat. However, anyone who has symptoms of strep throat or any other infection should behave as if they are contagious and follow procedures to prevent transmitting the infection.

An incubation period is the time between first developing an infection with the bacteria and beginning to show symptoms. The longer the incubation period, the easier it is for a person to transmit the infection to others without knowing it.

For most people, symptoms begin 2–5 days after exposure. In this time, a person could transmit the infection to many people, even when a person feels well.

Strep throat is contagious for the incubation period, as well as the time during which a person has symptoms, such as a fever. For some people who go without treatment, this can be significantly longer.

Taking antibiotics reduces the length of time a person is contagious.

People are more likely to be contagious if they:

  • are coughing or sneezing
  • do not wash their hands
  • are in close contact with others

Antibiotics reduce the time strep throat is contagious to about 1 day. However, the actual contagion period varies from person to person.

People will remain contagious until the antibiotics have killed enough bacteria to reduce the transmission risk.

A person should ask a doctor about how long to avoid other people and consider staying home until symptoms have disappeared.

A person should stay away from other people until they have been without fever, and not using fever medication, for at least 24 hours.

It is important to take antibiotics that specifically target group A strep bacteria. A person who uses someone else’s antibiotics or who takes antibiotics from a previous sickness may not get better and remain contagious for weeks.

Strep throat is more common among school-aged children and the adults who work with them, according to the Centers for Disease Control and Prevention (CDC).

Check any signs of strep throat with a doctor. The main symptoms are fever, swollen lymph nodes, and throat pain — usually without a cough. The sooner a person takes antibiotics, the less likely they are to transmit the infection to someone else.

Some other strategies to reduce the transmission of strep throat include:

  • staying at home from school or work if experiencing any symptoms of illness
  • avoiding sharing food and drinks with others
  • avoiding close contact with others
  • practicing frequent hand washing
  • disinfecting surfaces that a person frequently uses, such as sink handles, doorknobs, and toilets
  • covering the mouth when coughing or sneezing, ideally with a tissue
  • throwing used tissues in the trash

A person should see a doctor if they:

  • have severe symptoms of strep throat, such as a sore throat with a fever
  • have symptoms that do not get better after a doctor prescribes antibiotics
  • experience nausea, vomiting, or rash after taking antibiotics, which may signal a mild allergic reaction
  • develop dark urine, a rash, or a swollen face

The last three symptoms may be signs of a complication of strep throat called post-streptococcal glomerulonephritis. Very rarely, a person may have a severe allergic reaction to antibiotics.

Swelling of the face or throat, having trouble breathing, or experiencing seizures may be signs of a life threatening reaction. If a person experiences these symptoms, they should call 911 or go to the emergency room.

Strep throat is highly contagious.

Other infections that can cause a sore throat, such as the common cold, are also contagious.

People who have any symptoms of strep or another illness should assume they are contagious and avoid close contact with others. They should not wait for a doctor to confirm the infection or for a medical diagnosis.

With proper treatment, strep can go away in just a few days. Treatment also reduces the risk of serious complications, especially in older people and people with weak immune systems.

If a person has symptoms of strep throat, they should see a doctor as soon as possible.