Most Common Causative Organism of Acute Bacterial Tonsillitis
Group A Streptococcus (GAS, Streptococcus pyogenes) is the most common bacterial cause of acute tonsillitis, accounting for 20-30% of cases in children aged 5-15 years and 5-15% in adults. 1, 2
Epidemiologic Context
The majority of acute tonsillitis cases are viral in origin, but when bacterial infection occurs, GAS dominates:
- In children (5-15 years): GAS causes 20-30% of acute pharyngotonsillitis cases 2
- In adults: GAS accounts for only 5-15% of acute pharyngotonsillitis 1, 2
- Viral pathogens (adenovirus, influenza, parainfluenza, rhinovirus, respiratory syncytial virus, Epstein-Barr virus, enteroviruses) are responsible for the majority of all acute tonsillitis cases 2, 3
Other Bacterial Pathogens (Less Common)
While GAS is the predominant bacterial cause requiring antibiotic therapy, other organisms occasionally cause tonsillitis:
- Groups C and G beta-hemolytic streptococci can cause pharyngotonsillitis, though far less commonly than GAS 2, 4
- Staphylococcus aureus was the most frequently isolated organism (40.9%) in tonsillar core cultures from patients with recurrent tonsillitis undergoing tonsillectomy, though its role in acute infection versus chronic colonization remains unclear 5
- Arcanobacterium haemolyticum causes pharyngitis with scarlatiniform rash in adolescents and young adults 2, 3
- Mycoplasma pneumoniae and Chlamydia pneumoniae are sporadic causes 3
- Neisseria gonorrhoeae should be considered in sexually active patients with appropriate exposure history 3
Clinical Significance and Management Implications
Accurate identification of GAS is critical because it is the only common form of acute tonsillitis for which antibiotic therapy is definitively indicated. 3
Treatment goals for confirmed GAS tonsillitis include:
- Prevention of acute rheumatic fever (the primary goal) 1, 3
- Prevention of suppurative complications (peritonsillar abscess, cervical lymphadenitis, mastoiditis) 1
- Shortening of clinical course 3
- Reduction of transmission 1, 3
Diagnostic Approach
Microbiological confirmation is mandatory before prescribing antibiotics because clinical features alone cannot reliably distinguish viral from bacterial tonsillitis, even for experienced clinicians. 2
- Rapid antigen detection test (RADT): A positive test is diagnostic for GAS and warrants immediate treatment 2
- Throat culture: Remains the gold standard (90-95% sensitivity); in children and adolescents, a negative RADT must be followed by throat culture due to lower RADT sensitivity and the risk of missing rheumatic fever cases 2
- In adults: Backup throat culture after negative RADT is optional given low rheumatic fever risk 2
Common Pitfalls
- Do not treat based on clinical impression alone—this leads to unnecessary antibiotic use in 50-70% of cases because viral causes predominate 2
- Do not assume all exudative tonsillitis is bacterial—viruses (adenovirus, EBV) frequently produce exudative tonsillitis 2
- Avoid testing when obvious viral features are present (cough, rhinorrhea, hoarseness, conjunctivitis, oral ulcers)—testing in this context identifies asymptomatic GAS carriers rather than true infection 2