Strep throat is a bacterial infection of the throat and tonsils caused by group A Streptococcus, a type of bacteria that spreads through respiratory droplets and direct contact with an infected person’s saliva or nasal secretions. It accounts for 15% to 40% of sore throats in children ages 5 to 15, and 5% to 15% of sore throats in adults. Most sore throats are caused by viruses, but strep throat requires antibiotics to clear the infection and prevent rare but serious complications.
How Strep Throat Differs From a Viral Sore Throat
The distinction matters because the treatment is completely different. A viral sore throat runs its course on its own, while strep throat needs antibiotics. Fortunately, the two tend to look and feel different enough that doctors can narrow things down before even running a test.
Strep throat typically comes on fast. You may wake up with a severe sore throat that wasn’t there the night before, along with a fever over 100.4°F (38°C), swollen and tender lymph nodes at the front of your neck, and white patches or streaks of pus on your tonsils. Swallowing often feels painful rather than just scratchy.
What’s notably absent with strep is just as telling. If you have a cough, runny nose, hoarseness, or pink eye, a virus is the more likely culprit. Strep throat is an infection of the throat specifically, so it doesn’t produce the upper respiratory symptoms that come with a cold or flu. Doctors use this pattern (fever, swollen nodes, tonsillar pus, and no cough) as a four-point scoring system to estimate the likelihood of strep before ordering a test. The more of those four features you have, the higher the probability.
Who Gets Strep Throat
Children between 5 and 15 are by far the most affected group. In this age range, strep causes up to 40% of all sore throats, largely because schools and group settings make transmission easy. Adults still get strep, but the bacteria is responsible for a smaller share of their sore throats, closer to 5% to 15%. Adults who live or work closely with children, including parents and teachers, face higher exposure.
Strep throat peaks in late fall through early spring, overlapping with cold and flu season, which is part of why it’s so often confused with viral illnesses.
How It Spreads
The bacteria travel primarily through respiratory droplets released when an infected person coughs, sneezes, or talks. You can also pick it up by touching a surface contaminated with those droplets and then touching your mouth or nose, or by sharing utensils, cups, or food with someone who’s infected. Close, prolonged contact increases the risk, which is why outbreaks cluster in households, classrooms, and dormitories.
A person with untreated strep throat is contagious for as long as they have symptoms. Once antibiotics are started, that window shrinks dramatically. Most people are no longer contagious within 12 hours of their first dose, which is why schools and daycares typically allow children to return after that 12-hour mark.
Getting Tested
Because symptoms alone can’t confirm the diagnosis with certainty, testing is standard. The most common first step is a rapid antigen detection test, often called a “rapid strep test.” A provider swabs the back of your throat and tonsils, and results come back in minutes. These rapid tests are highly specific, meaning a positive result is reliable, but they catch about 82% of true infections. That means roughly 1 in 5 cases can be missed.
When the rapid test is negative but strep is still suspected (especially in children), a throat culture may be sent to a lab. Cultures take one to two days to return results but are considered the gold standard. Newer molecular tests that detect the bacteria’s genetic material are even more sensitive, catching about 97% of infections, though they’re not yet available everywhere.
Treatment and Recovery
Strep throat is treated with a 10-day course of antibiotics. Penicillin and amoxicillin are the first-choice options and have remained effective against group A strep for decades. For people with a penicillin allergy, alternative antibiotics are available.
Most people start feeling noticeably better within one to two days of beginning treatment, but finishing the full 10 days is important. Stopping early can allow the bacteria to survive and increases the risk of complications. During recovery, over-the-counter pain relievers can help manage throat pain and fever, and warm liquids or cold foods like popsicles can soothe discomfort.
Without antibiotics, strep throat usually resolves on its own within a week, but leaving it untreated isn’t recommended. The antibiotics shorten the illness, reduce contagiousness, and protect against the more serious problems strep can trigger.
Complications Worth Knowing About
The main reason strep throat is taken seriously isn’t the sore throat itself. It’s what can follow if the infection goes untreated. The bacteria’s surface proteins closely resemble certain proteins in human tissue, particularly in the heart. The immune system, while fighting off the infection, can mistakenly attack the body’s own cells in a process called molecular mimicry.
The most well-known complication is rheumatic fever, which typically develops 10 to 28 days after the throat infection. Rheumatic fever can cause joint pain, skin rashes, and inflammation of the heart. Repeated episodes lead to permanent heart valve damage (rheumatic heart disease) in up to 60% of those affected, sometimes manifesting years or even decades later. In the United States, rheumatic fever has become extremely rare, occurring in roughly 1 in a million people, thanks largely to widespread antibiotic treatment. It remains a significant concern in parts of the world with less access to healthcare.
Strep can also trigger kidney inflammation, usually appearing one to three weeks after the infection. This typically causes dark or reduced urine, swelling in the face or legs, and elevated blood pressure. Most cases, especially in children, resolve fully with supportive care.
Closer to the throat itself, untreated strep can lead to an abscess forming behind the tonsils, which causes worsening one-sided throat pain, difficulty opening the mouth, and a muffled voice. This requires drainage and is one of the more common local complications.
Preventing the Spread
There is no vaccine for group A strep. Prevention comes down to basic hygiene: frequent handwashing, not sharing cups or utensils, and covering coughs and sneezes. If someone in your household has strep, replacing their toothbrush after 24 hours on antibiotics and keeping their drinking glasses separate can reduce transmission to other family members.
If you’ve been in close contact with someone diagnosed with strep and develop a sore throat with fever, getting tested early allows for prompt treatment and limits how far the bacteria can spread.