Strep throat is caused by an infection with a bacteria called group A Streptococcus pyogenes, or Strep. The infection affects the tonsils and back of the throat, causing an acute sore throat and potentially other symptoms. It is worth noting that this is a bacterial infection, not a viral one.
It's important to keep these two types separate so you'll know what kind of treatment to seek.
A sore throat is a more general term for any kind of pain in the throat; it's also called acute pharyngitis. Sore throats can be caused by infection with various bacteria and viruses, the most common being an upper respiratory infection such as a cold or the flu. It can also result from allergies, smoking, and other environmental irritants, like extremely dry or cold air. Strep infections cause a sore throat, but Strep bacteria specifically cause them.
About 80% of the time, sore throats are caused by respiratory viruses such as adenovirus, rhinovirus, parainfluenza virus, respiratory syncytial virus, and others. Typically, pharyngitis will go away naturally as you recover from the viral infection. Strep throat can also resolve on its own.
Still, it requires specific treatment to ensure that you recover quickly and without complications.
Every year, millions of people get strep throat. About 1–2% of emergency visits¹ in the US are for sore throats, and 5–15% of adults and 15–35% of children with a sore throat are diagnosed with strep pharyngitis. It is considered a very common disease and generally considered mild, although exceptions exist.
Strep is not airborne and is primarily spread through direct person-to-person transmission². The bacteria primarily lives in the throat and can be spread through saliva or nasal secretions. It can also be transmitted via air droplets when an infected person sneezes or coughs.
Most people catch strep throat by hanging out with somebody who already has it or through the physical play between children. You can even give it to someone else before developing any symptoms.
It is rarely spread by fomites, meaning from surfaces or shared plates and toys. However, it has, uncommonly, been shown to be transmitted via food, with outbreaks resulting from improper hygiene and food preparation.
Strep cannot be caught or transmitted by animals such as pets. The bacteria does not infect any other species but is carried by sick or asymptomatic individuals who do not know they have it.
Strep throat is highly contagious. It easily transmits in daycare centers, schools, and other places where people, especially children, congregate. Because of this, the CDC recommends staying home from work or school until you have no fever and it has been 12 hours since you started treatment. Your doctor may recommend waiting for 24 hours.
The incubation period is two to five days before you show symptoms. You are contagious toward the end of this time, even though you do not yet know you are infected.
Some people are asymptomatic carriers, meaning they live with the bacteria in their throat and are not sick. Still, they are much less likely to spread it to others. This can be an issue because doctors may prescribe antibiotics to carriers unnecessarily, typically because they have an acute viral infection and test positive. This contributes to antibiotic overuse and potential resistance.
If you or your child have other symptoms but are known to be carriers or always test positive for strep, ask if you need antibiotics. Some carriers end up being treated every time they have a sore throat.
Once you have started antibiotics, you are unlikely to still be contagious after 12 hours. However, you should avoid activities that could result in the exchange of saliva, such as sharing eating utensils or kissing.
The vast majority of strep infections are found in school-age children. This is in part because of the crowded conditions in typical schools and daycares and also because children are not as good at remembering to cover their mouths when sneezing or coughing. Young children also tend to wipe their noses with their hands.
Also at risk are adults who are in frequent contact with children, such as parents, teachers, and youth workers. People living in crowded conditions, such as dorms, military barracks, shelters, and prisons, are also at increased risk.
The classic presentation of strep pharyngitis is an intense sore throat that comes on very quickly. However, other symptoms are likely to be present, which include:
Pain when swallowing
Painful and/or swollen lymph glands in the neck
Red and swollen throat and tonsils
White patches (pus) on the tonsils
Loss of appetite
Skin rash, which is referred to as scarlet fever¹
Fatigue, or generally feeling ill
Some symptoms indicate the infection is less likely due to Strep, primarily cough, hoarseness, conjunctivitis, oral ulcers, and a runny nose. These usually accompany viral infections, although there is some overlap between symptoms of both causes.
Sore throat plus a cough is much more likely to be a cold, for example, which is caused by a virus. Sore throat on its own, or with the other characteristic symptoms mentioned, warrants checking for Strep.
In most cases, strep throat is not a serious condition. However, untreated strep throat can lead to acute rheumatic fever, especially in children aged 5 to 15 years² and more likely in resource-limited countries and communities where the social determinants of health play a greater role. It is rare for this to happen in adults, and strep pharyngitis is usually self-limited.
Acute rheumatic fever is an immune system response that can impact sites distant from the initial infection. Symptoms include:
Shortness of breath
Painful and tender joints
Uncontrollable body movements
A rash or painless lumps near joints
The primary reason for treating strep pharyngitis is to prevent rheumatic heart disease, which can lead to serious problems with the valves in your heart.
Another sequela of strep infections is post-streptococcal glomerulonephritis (PSGN), although it is uncommon. This complication is also caused by a dysfunctional immune system response that damages the kidneys. Unlike rheumatic fever, antibiotic treatment has not been shown to prevent PSGN.
PSGN can show up about 1 to 3 weeks after strep pharyngitis³ (and can also occur 3–6 weeks after a streptococcal skin infection). Potential warning signs are:
Dark, reddish-brown urine
Swelling of the face, hands, and feet
Decreased frequency of urination and/or quantity of urine
High blood pressure
Some people with PSGN may have mild symptoms, and most recover after a few weeks with no problems. In some cases, long-term kidney damage can occur.
There can be other complications, including the development of a peritonsillar abscess, severe ear infections, and mastoiditis. The former is a deeper infection of the head and neck, with symptoms including fever, sore throat, difficulty swallowing, and changes in the voice. Streptococcal ear infections can lead to an infection of the mastoid bone behind the ear.
Any of these can be quite serious and may require hospitalization or even surgery. Treating strep throat with antibiotics as soon as it is diagnosed can help prevent some complications.
In rare cases, the bacteria may move through the bloodstream and lymphatic system⁴ to other body parts, causing an invasive strep infection⁵. Examples of this would be necrotizing fasciitis or streptococcal toxic shock syndrome.
These life-threatening conditions most often occur in people with chronic illnesses such as cancer, diabetes, and kidney failure or in those immunocompromised or on steroids. Rarely, breaks in the skin can lead to an invasive infection in healthy people.
Other post-strep complications include pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections⁶ (PANDAS). These can manifest as sudden onset obsessive-compulsive disorder and/or tics, and sometimes other behavioral symptoms. PANDAS is somewhat controversial and needs more study to be fully understood.
Post-streptococcal reactive arthritis⁷(PSRA) is inflammatory arthritis of one or more joints. It's not the same as acute rheumatic fever and occurs in people aged eight to 14 and 21 to 37. Unlike acute rheumatic fever, in which arthritis typically lasts a short period, PSRA can have prolonged or recurrent joint symptoms.
In adults, even untreated strep throat is unlikely to lead to complications. However, it is worth remembering that it is highly contagious.
Scarlet fever | Centers for Disease Control and Prevention
Acute rheumatic fever (2021)
Several factors increase the chance of becoming infected with Strep and developing pharyngitis.
Strep throat is very common in children older than age three. But it has been diagnosed in younger children, even infants. The primary risk factors are:
Having close contact with somebody with a strep infection, such as being in the same household
Age between five and 15 years
Living or working in a crowded environment
Being a parent of a school-age child or in frequent contact with children
Anyone can get strep throat, regardless of how healthy you are. However, some people are prone to recurring strep throat and may have their tonsils removed. One study¹ showed that children with recurring strep throat produced fewer antibodies to Strep bacterial toxin and may also have been producing cytotoxic T cells that were harming their B immune cells.
In other words, there is a genetic immune system dysfunction involved.
Typically, diagnosing strep throat is a two-stage process.
First, the doctor will evaluate for other possibilities, such as a viral infection. Some symptoms, such as a cough, typically do not occur with strep throat. If these symptoms are present, testing for Strep is sometimes not indicated.
If there are very few symptoms of a cold or other viral infection, or when there has been an exposure to someone with strep pharyngitis, then diagnostic testing is performed. There are two commonly used diagnostic tests, both of which are performed using a soft swab applied to the tonsils and the back of the throat.
Rapid antigen tests can give results in the medical office within 30 minutes. However, they are prone to false negatives. Throat cultures require that the swab be sent to the lab, and it takes one to two days to get results. However, bacterial cultures are considered the gold standard for diagnosing strep pharyngitis.
The swabs are taken from the medical office and then shipped to the lab, where they are cultured to see if the bacteria grows. Once the presence of Strep is identified, the diagnosis is sure. This has high sensitivity and specificity and low cost.
Typically, the rapid test is the one you will get first. If it is positive, treatment will be started right away. If negative, a throat culture will usually be sent to the lab for confirmation that there is no evidence of strep infection.
Future testing methods, including more accurate rapid tests², point-of-care PCR³, and smartphone imaging technology⁴, will help with earlier detection, preventing antibiotic overuse and infection complications.
Strep throat can be treated with antibiotics, and most people recover within a few days once they have started the medication. Treatment also makes you much less contagious.
The go-to treatment for strep throat is penicillin or amoxicillin. Unlike some bacteria, there is no evidence of Streptococcus pyogenes developing resistance to these older, very common antibiotics. The newer drugs have not been shown to be more effective.
Typically, the routine is oral penicillin V, oral amoxicillin, or intramuscular benzathine penicillin G, depending on the severity of the infection and other factors.
If you are allergic to penicillin, other agents can be used. These include cephalexin and cefadroxil. Yes, it is more complicated to treat strep throat if you have a penicillin allergy. As a note, penicillin allergy¹ does not always persist for life, and it is worth getting tested to see if you are still allergic to prevent your doctor from having to prescribe less-effective drugs.
Ideally, you should get this done when you are healthy and not wait until you have an infection.
Your doctor might also recommend acetaminophen or an anti-inflammatory like ibuprofen to reduce fever and control pain. Corticosteroids are not recommended, as they can weaken the immune system, and it can take longer to get over the infection.
Throat lozenges or numbing sprays can be prescribed or bought over the counter to help ease symptoms in the first few painful days.
You should not hesitate to be treated because of concerns over antibiotic overuse; a positive test for Strep indicates that you have a bacterial infection treated with antibiotics.
If your symptoms do not improve within a few days after starting the medicine, you should go back to your doctor. You may need to take a different antibiotic. While S. pyogenes has not developed resistance to penicillin, it can be resistant to some antibiotics used for people who cannot take penicillin.
Taking the full course of antibiotics as prescribed is the best way to treat your strep infection. And there are also a few things you can do at home² to help you better deal with the symptoms.
Some suggestions include:
Gargle every hour with warm salt water, using one teaspoon of table salt in one cup of warm water. This helps reduce swelling and pain.
Use an over-the-counter anesthetic throat spray or regular throat lozenges.
Drink plenty of fluids, and include warm fluids such as tea or soup. It is important to stay hydrated whenever you are sick, and drinking fluids keep your throat from drying out, making it more painful.
Avoid crunchy food such as potato chips or anything you find difficult to swallow. If swallowing is painful, go for soft foods.
Eat flavored ice pops, ice cream, scrambled eggs, sherbet, and gelatin dessert, all of which can help soothe your throat.
Take it easy and get plenty of rest.
Don't smoke, and don't let others smoke around you. Remember that smoking causes all kinds of health problems, and you should talk to your doctor about quitting. Your doctor might also suggest using a nicotine patch to handle cravings instead of smoking.
Consider using a humidifier in your bedroom to add moisture to the air and keep your throat from drying out at night.
Honey has been shown to have anti-inflammatory properties³ that can also help a sore throat. Taking warm water or tea with honey and lemon is very soothing.
Again, antibiotics are the go-to treatment, but these home care tips can help you with the unpleasant symptoms of strep throat while you recover. It's worth trying anything that has worked to soothe your sore throat in the past. Make sure to get plenty of fluids and rest.
Although it is safe to go back to work after starting treatment, you will heal faster if you can rest as much as possible until you are back to normal.
Be aware that some people may develop stomach issues from the negative impact of antibiotics on your microbiome. If this is the case, eating plain yogurt or any other fermented food that contains probiotics can help replenish your beneficial gut bacteria.
Preventing strep throat overlaps with prevention methods for many other contagious diseases. Particularly, if you are at risk, you should:
Practice good hand hygiene. Teach children the importance of washing their hands every time they go to the bathroom, before eating, and after coughing, sneezing, or touching their noses.
Cough or sneeze into your upper sleeve or elbow, not your hands.
Wash glasses, utensils, and plates after someone sick uses them.
Do not share drinks or food with anyone who is sick.
Dispose of used tissues properly.
Overall, strep throat is best prevented by practicing good hygiene. Remember that the bacteria is not airborne over long distances but can pass to others through droplets in the air when they cough or sneeze.
For the most part, you need to have fairly close contact with somebody who already has a strep infection to become infected. You can prevent it from spreading through your family by ensuring that everyone practices good hand and respiratory hygiene.
You should see a doctor if you or your child has a rapid-onset sore throat that is either on its own or accompanied by the typical symptoms of strep throat. If you also have coughing, sneezing, or a runny nose, and you have been exposed to someone with similar symptoms, it is probably a cold. You do not need to see a doctor unless you have a high fever, respiratory difficulty, or dehydration.
Your family doctor or pediatrician typically treats strep throat. Complications in the aftermath of a streptococcal infection, such as acute rheumatic fever, will require a referral to a specialist such as a cardiologist.
Most people will not have to see any specialist, as strep infections are almost always treated successfully with antibiotics. Strep throat can usually be tested for and treated in any walk-in clinic. However, it is typically best to go to your primary care clinician if you can.