Strep throat is a bacterial infection of the throat and tonsils caused by group A Streptococcus bacteria. It accounts for a significant share of sore throats, particularly in children: globally, an estimated 288.6 million episodes occur in children ages 5 to 14 each year. Among all patients who show up with a sore throat, roughly 37.6% test positive for strep.
How Strep Throat Feels Different From a Viral Sore Throat
Most sore throats are caused by viruses, and the distinction matters because only the bacterial version needs antibiotics. Strep throat tends to come on fast. The classic pattern is a sudden fever, intense throat pain, and swollen lymph nodes in the front of the neck, all without a cough. If you also notice white or yellow patches on your tonsils, tiny red spots on the roof of your mouth, or a swollen uvula, strep becomes more likely.
Viral sore throats, by contrast, typically arrive alongside a cough, runny nose, or hoarseness. Having even one of those viral symptoms lowers the chance of strep, dropping the test positivity rate to about 28%. With all three viral symptoms present, it drops further to around 23%. Still, viral symptoms don’t completely rule strep out, which is why testing matters.
How Doctors Decide Whether to Test
Clinicians often use a scoring system called the Centor score to gauge how likely strep is before ordering a test. You get one point for each of the following: fever, no cough, swollen and tender lymph nodes in the front of the neck, and white patches on the tonsils. A modified version of the score adds a point if you’re under 15 and subtracts one if you’re 45 or older, reflecting the fact that strep is far more common in kids.
With a score of 0 or 1, strep is unlikely enough that testing and treatment are generally skipped. A score of 2 or 3 warrants a rapid test. At a score of 4, some guidelines support starting antibiotics right away even before results come back.
Rapid Tests and Throat Cultures
The most common first step is a rapid antigen test, the familiar throat swab that returns results in minutes. These tests are highly specific, meaning a positive result is very reliable. Their sensitivity, however, sits around 82%, so they miss roughly 1 in 5 true cases. If your rapid test comes back negative but strep is still strongly suspected, a throat culture (which takes one to two days) can catch what the rapid test missed.
Newer molecular tests that detect bacterial DNA are significantly more accurate, with sensitivity around 97% and specificity around 95%. These are becoming more widely available and can return results nearly as fast as the traditional rapid test.
Treatment and Recovery Timeline
Antibiotics are the standard treatment. The first-choice options are penicillin and amoxicillin, both taken for a full 10-day course. If you have a penicillin allergy, alternatives are available. Finishing the entire course matters even after you feel better, because stopping early can leave bacteria behind and increase the risk of complications.
Most people start feeling noticeably better within one to two days of starting antibiotics. Pain relievers and anti-inflammatory medications can help manage the fever and throat pain in the meantime. Cold fluids, warm broths, and soft foods tend to be easier to swallow while your throat is at its worst.
How Long You’re Contagious
Without treatment, strep throat can remain contagious for weeks. Once you start antibiotics, you’re generally no longer contagious within 12 hours. That’s the standard cutoff used by schools and child care centers for allowing kids to return. The bacteria spread through respiratory droplets (coughing, sneezing, sharing drinks), so hand washing and avoiding shared utensils are the main ways to limit transmission in a household.
Scarlet Fever: Strep With a Rash
Some strep infections produce a toxin that triggers a distinctive rash known as scarlet fever. The rash feels rough, like sandpaper, and typically starts on the neck, underarms, and groin before spreading across the body. Skin creases in the elbows, underarms, and groin often turn a deeper red. Despite its alarming name, scarlet fever is treated with the same antibiotics as regular strep throat and resolves on the same timeline.
Complications of Untreated Strep
The main reason strep throat requires antibiotics, beyond symptom relief, is to prevent serious complications. An estimated 1% to 3% of people with untreated strep infections develop rheumatic fever, an inflammatory condition that can damage the heart valves. Of those who develop rheumatic fever, up to 60% go on to have lasting heart damage. This is rare in countries where antibiotics are readily available, but it remains a major concern globally.
A kidney complication called post-streptococcal glomerulonephritis can develop about 10 days after strep symptoms begin. Signs include dark reddish-brown urine, decreased urine output, swelling (especially around the eyes, hands, and feet), high blood pressure, and fatigue. Unlike rheumatic fever, this kidney condition can occasionally occur even after appropriate antibiotic treatment, though most cases resolve on their own over several weeks.
Other potential complications include peritonsillar abscess (a pocket of pus forming near the tonsil) and, rarely, the infection spreading to the sinuses, ears, or bloodstream. These complications are uncommon when strep is caught and treated early, which is why getting tested when symptoms fit the pattern is worthwhile.