Tonsillitis is usually caused by a viral infection , but it can also be caused by bacteria , especially streptococcus (“strep throat”). Common viral causes include the same germs that cause colds and flu, and some cases are linked to Epstein-Barr virus.

Quick scoop

  • Most common cause: viruses.
  • Bacterial cause: streptococcus is a common one.
  • How it spreads: the infections that cause tonsillitis can spread from person to person.
  • Typical symptoms: sore throat, fever, trouble swallowing, and swollen tonsils.

If you mean a specific case, the key clue is that viral tonsillitis often comes with cold-like symptoms, while bacterial tonsillitis may be more likely to need medical treatment.

When to get help

Seek urgent care if there is trouble breathing, drooling, or an inability to swallow saliva or liquids.

Bottom line

Tonsillitis is an inflammation of the tonsils most often triggered by a virus, but sometimes by bacteria.