Tonsillitis is an infection of the tonsils. Most cases are caused by viruses. But when bacteria are responsible, group A Streptococcus (Streptococcus pyogenes) is the most common cause. This is what people call strep throat. Other bacteria can also cause tonsillitis, though less frequently.
What bacteria causes tonsillitis strep and beyond?
The short answer is group A Streptococcus. It accounts for the majority of bacterial tonsillitis cases. Other bacteria include groups C and G Streptococcus, Fusobacterium necrophorum, Arcanobacterium haemolyticum, and rarely Neisseria gonorrhoeae or Corynebacterium diphtheriae. Each has a different profile in terms of age group, severity, and complications.
Group A strep produces a toxin that causes the classic symptoms: sudden sore throat, fever, swollen tonsils with white patches, and tender lymph nodes in the neck. It is most common in children ages 5 to 15, but it can affect adults too. Without treatment, it can lead to rheumatic fever or kidney inflammation.
Other streptococci — groups C and G — can cause similar but often milder symptoms. Fusobacterium necrophorum is a less common but dangerous cause, especially in teens and young adults. It can lead to a serious infection called Lemierre’s syndrome. Arcanobacterium haemolyticum mostly affects teenagers and can mimic strep throat with a rash.
How does strep throat differ from viral tonsillitis?
Pain alone does not tell you if the cause is bacterial or viral. Doctors look for a pattern of symptoms. Strep throat often comes on quickly with high fever, swollen and tender lymph nodes, and white or yellow spots on the tonsils. Cough, runny nose, and hoarseness are usually absent in strep but common in viral infections.
A rapid strep test or throat culture is the only way to confirm group A strep. The rapid test gives results within minutes but can miss some infections. A throat culture takes 24 to 48 hours but is more accurate. Many doctors use the rapid test first and confirm with culture if the test is negative but symptoms are strong.
Do not assume all sore throats need antibiotics. Viral tonsillitis will not respond to antibiotics. Taking them unnecessarily does not help and can cause side effects or contribute to antibiotic resistance.
What other bacteria can cause tonsillitis besides strep?
Several bacteria besides group A strep can infect the tonsils. They are less common, but some carry serious risks.
Groups C and G Streptococcus. These bacteria can cause pharyngitis similar to strep. Outbreaks have been reported in college students and adults. Treatment with antibiotics is the same as for group A strep.
Fusobacterium necrophorum. This bacterium lives in the mouth normally. When it invades the tonsils, it can cause a severe infection that spreads to the jugular vein. This is Lemierre’s syndrome, a rare but life-threatening illness. Symptoms include severe sore throat, high fever, and neck swelling that worsens over days. Young adults ages 15 to 25 are at highest risk.
Arcanobacterium haemolyticum. This causes a sore throat that can look exactly like strep. It often comes with a fine red rash that mimics scarlet fever. It is most common in teenagers and young adults. Standard antibiotics for strep usually work, though some strains need different drugs.
Neisseria gonorrhoeae. This causes gonococcal pharyngitis. It happens in sexually active adults, especially those who have oral sex with an infected partner. Most cases have no symptoms, but some cause a persistent sore throat. Treatment is with different antibiotics than for strep.
Corynebacterium diphtheriae. Diphtheria is rare in countries with routine vaccination. It causes a thick gray coating on the tonsils that can block the airway. Vaccination prevents it, but cases still occur in unvaccinated individuals or travelers.
Anaerobic bacteria. Mixed infections with mouth anaerobes can cause peritonsillar abscess, a collection of pus behind the tonsil. This causes severe pain, difficulty opening the mouth, and a “hot potato” voice. It requires drainage and antibiotics.
How is bacterial tonsillitis treated?
Antibiotics are the main treatment for bacterial tonsillitis when the cause is confirmed or strongly suspected. Penicillin or amoxicillin taken for 10 days is the standard for group A strep. This shortens the illness, reduces spread, and prevents complications like rheumatic fever.
For people allergic to penicillin, alternatives include cephalexin, clindamycin, or azithromycin. The choice depends on the bacteria and allergy history.
It is important to finish the full course even if symptoms improve. Stopping early can allow the bacteria to survive and increase the risk of complications or recurrence.
Some people carry group A strep without symptoms. This is called being a carrier. Carriers do not usually need antibiotics because they are not sick and are not highly contagious. Testing can tell the difference between a true infection and carriage.
For viral tonsillitis, antibiotics do not help. Treatment focuses on pain relief with ibuprofen or acetaminophen, warm salt water gargles, and rest. Some doctors recommend a short course of steroids to reduce swelling, but this is not routine for uncomplicated cases.
When should you see a doctor for tonsillitis?
Most sore throats get better on their own within a week. But certain signs point to a bacterial infection that needs medical attention. See a doctor if you or your child have:
- A sore throat that lasts more than 2 days
- Fever above 101°F (38.3°C)
- White or yellow patches on the tonsils
- Swollen, tender lymph nodes in the neck
- No cough or runny nose
- Difficulty swallowing or breathing
- A rash
- Recent exposure to someone with strep throat
Children under 3 years old usually do not get strep throat. But they can get bacterial tonsillitis from other germs. If a young child has fever and a foul-smelling discharge from the nose, a different type of bacterial infection may be present.
Adults with recurring or severe tonsillitis may benefit from a throat culture or a test for Fusobacterium necrophorum if strep tests are negative.
Frequently Asked Questions
Can tonsillitis be caused by bacteria other than strep?
Yes. Groups C and G streptococci, Fusobacterium necrophorum, and Arcanobacterium haemolyticum are examples. Each is less common but can produce similar symptoms.
How can I tell if my throat infection is bacterial or viral?
Symptoms overlap, but bacterial infections often come with high fever, swollen lymph nodes, and white patches on the tonsils without cough or runny nose. A rapid strep test or throat culture is the only reliable way to know.
Does bacterial tonsillitis always need antibiotics?
When strep is confirmed, antibiotics are recommended to prevent rheumatic fever. For other bacteria like groups C and G, antibiotics also speed recovery. However, some mild bacterial infections may clear on their own.
What happens if strep throat is not treated?
Untreated strep throat can lead to rheumatic fever, which damages heart valves, or post-streptococcal glomerulonephritis, a kidney disease. These complications are rare but serious. Antibiotics almost completely prevent them.
