The Facts
Tonsillitis is an infection of the tonsils that causes inflammation. It's most common in children aged three to seven, who have larger tonsils than adults and older children. The tonsils are made of lymphatic tissue. Their job is to produce antibodies that fight infections. Ironically, such tissue is quite prone to becoming infected itself.
Many cases of tonsillitis never reach the doctor's office. However, tonsillectomy (tonsil removal) is still one of the most common childhood operations; 1 of every 10,000 people under 18 years of age have their tonsils removed each year. But this number is down from 48 in every 10,000 people under 18 years of age in 1994. Tonsillectomy is considered a last resort these days.
Causes
There are three common causes of tonsillitis:
Group A Streptococcus - These common bacteria infect the throats of one person in five, including adults. Many people have no symptoms. They can still transmit the bug, however. Group A Streptococcus is the most common of all bacteria that can cause disease, and is also responsible for strep throat. It's also capable under some circumstances of causing more serious illness. Group A Streptococcus probably accounts for most cases of tonsillitis, and is the kind most likely to cause complications.
Various respiratory viruses, especially cold and flu viruses, account for most of the rest of cases of tonsillitis. These infections can be sometimes milder than bacterial infections.
Infectious mononucleosis, caused by the Epstein-Barr virus, can often include symptoms of inflamed tonsils. Among younger children, the symptoms normally associated with mononucleosis in adults are often absent, but tonsillitis is common.