Tonsillitis is most often caused by common viruses, but bacterial infections also can be the cause. The most common bacterium causing tonsillitis is Streptococcus pyogenes (group A streptococcus), the bacterium that causes strep throat. Other strains of strep and other bacteria also may cause tonsillitis.

How do you catch tonsillitis?

Tonsillitis is most often spread when someone in your vicinity with the infection sneezes or coughs and you inhale the droplets. However, you can also contract tonsillitis if you touch a doorknob or other contaminated object and then touch your mouth or nose.

What causes tonsillitis to form?

The tonsils combat bacteria and viruses that enter your body through your mouth and nose. However, tonsils are also vulnerable to infection from these invaders. Tonsillitis can be caused by a virus, such as the common cold, or by a bacterial infection, such as strep throat.