Tonsillitis refers to inflammation of the tonsils.

The most common cause of tonsillitis is a viral infection. Viral infections do not require or respond to antibiotics. 

The most common cause of bacterial tonsillitis is group A streptococcus (Streptococcus pyogenes). This can be effectively treated with penicillin V (phenoxymethylpenicillin). The second most common bacterial cause of tonsillitis is Streptococcus pneumoniae.

Other causes:

  • Haemophilus influenzae
  • Moraxella catarrhalis
  • Staphylococcus aureus


Waldeyer’s Tonsillar Ring

In the pharynx, at the back of the throat, there is a ring of lymphoid tissue. There are six areas of lymphoid tissue in Waldeyer’s ring, comprising of the adenoidstubal tonsilspalatine tonsils and the lingual tonsil. The palatine tonsils are the ones typically infected and enlarged in tonsillitis. These are the tonsils on either side at the back of the throat.



A typical presentation of acute tonsillitis is with:

  • Sore throat
  • Fever (above 38°C)
  • Pain on swallowing


Examination of the throat will reveal red, inflamed and enlarged tonsils, with or without exudates. Exudates are small white patches of pus on the tonsils. 

There may be anterior cervical lymphadenopathy, which refers to swollen, tender lymph nodes in the anterior triangle of the neck (anterior to the sternocleidomastoid muscle and below the mandible). The tonsillar lymph nodes are just behind the angle of the mandible (jawbone). 


Centor Criteria

The Centor criteria can be used to estimate the probability that tonsillitis is due to bacterial infection and will benefit from antibiotics.

A score of 3 or more gives a 40 – 60 % probability of bacterial tonsillitis, and it is appropriate to offer antibiotics. A point is given if each of the following features are present:

  • Fever over 38ºC
  • Tonsillar exudates
  • Absence of cough
  • Tender anterior cervical lymph nodes (lymphadenopathy)


FeverPAIN Score

The FeverPAIN score is an alternative to the Centor criteria. A score of 2 – 3 gives a 34 – 40% probability, and 4 – 5 gives a 62 – 65% probability of bacterial tonsillitis:

  • Fever during previous 24 hours
  • PPurulence (pus on tonsils)
  • AAttended within 3 days of the onset of symptoms
  • IInflamed tonsils (severely inflamed)
  • NNo cough or coryza



Consider admission if the patient is immunocompromisedsystemically unwelldehydrated, has stridorrespiratory distress or evidence of a peritonsillar abscess or cellulitis.

When tonsillitis is the most likely diagnosis, calculate the Centor criteria or FeverPAIN score.

Educate patients with likely viral tonsillitis and give safety net advice about when to seek medical advice. Advise simple analgesia with paracetamol and ibuprofen to control pain and fever. NICE clinical knowledge summaries suggest advising patients to return if the pain has not settled after 3 days or the fever rises above 38.3ºC. Starting antibiotics or an alternative diagnosis should be considered.

Consider prescribing antibiotics if the Centor score is ≥ 3, or the FeverPAIN score is ≥ 4. Also, consider antibiotics if they are at risk of more severe infections, such as young infants, immunocompromised patients or those with significant co-morbidity, or a history of rheumatic fever.

Delayed prescriptions can be considered. This involves educating patients or parents about the likely viral nature of the sore throat and providing a prescription to be collected only if the symptoms worsen or do not improve in the next 2 – 3 days.


Choice of Antibiotic

Penicillin V (also called phenoxymethylpenicillin) for a 10-day course is typically first-line. It has a relatively narrow spectrum of activity and is effective against Streptococcus pyogenes.

Clarithromycin is the usual first-line choice in true penicillin allergy. 



  • Peritonsillar abscess, also known as quinsy
  • Otitis media, if the infection spreads to the inner ear
  • Scarlet fever
  • Rheumatic fever
  • Post-streptococcal glomerulonephritis
  • Post-streptococcal reactive arthritis


Last updated July 2021
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