Differential Diagnosis for Tonsillar Exudate
The presence of exudate on tonsils is not specific for bacterial infection and requires microbiological confirmation with throat culture or rapid antigen detection testing before initiating antibiotic therapy, as viral infections frequently produce identical findings. 1, 2
Primary Differential Diagnoses
Bacterial Causes
Group A β-hemolytic Streptococcus (Streptococcus pyogenes) is the most important bacterial pathogen, accounting for 15-30% of cases in children aged 5-15 years and 5-15% in adults, though it represents only 20% of all tonsillar exudate cases overall 1, 3, 4
Fusobacterium necrophorum is increasingly recognized as a significant pathogen, recovered from 58% of peritonsillar abscess aspirates and 56% of tonsillar cores in acute cases, with patients showing significantly higher inflammatory markers (CRP and neutrophil counts) compared to other bacterial infections 5
Polymicrobial infections involving anaerobes and beta-lactamase producing bacteria occur in up to 75% of recurrent tonsillitis cases, which can shield Group A streptococcus from penicillin therapy 6
Viral Causes
Viral infections account for 70-95% of all tonsillitis cases and commonly produce tonsillopharyngeal exudates that are clinically indistinguishable from bacterial infections 3, 4
Epstein-Barr virus (infectious mononucleosis) causes approximately 4% of peritonsillar abscess cases and can present with prominent tonsillar exudates, often with superimposed bacterial infection 5, 7
Other viral pathogens including adenovirus, herpes simplex virus, influenza, and respiratory syncytial virus can all produce exudative tonsillitis 5
Less Common but Important Causes
Necrotizing tonsillitis is a rare complication that can occur with viral-bacterial superinfection, particularly EBV with Group A streptococcus, requiring imaging for diagnosis 7
Peritonsillar abscess should be considered when exudate is accompanied by severe unilateral tonsillar swelling, uvular deviation, or trismus, with 52% of parapharyngeal abscesses having concomitant peritonsillar involvement 5
Diphtheria (in unvaccinated populations) presents with adherent gray pseudomembrane rather than typical exudate 1
Clinical Features That Guide Diagnosis
Findings Suggesting Bacterial (Streptococcal) Etiology
Sudden-onset sore throat with pain on swallowing, fever (though fever is not constant and its absence does not exclude bacterial infection), tonsillopharyngeal erythema with or without exudates, beefy red swollen uvula, soft palate petechiae ("doughnut lesions"), and tender enlarged anterior cervical lymph nodes 1, 2, 8
Age 5-15 years, presentation in winter or early spring, history of exposure to documented streptococcal infection, and absence of viral symptoms 1
Findings Strongly Suggesting Viral Etiology
Presence of conjunctivitis, coryza (clear watery nasal discharge), hoarseness, cough, diarrhea, or characteristic viral exanthems/enanthems 1, 9
Discrete ulcerative stomatitis or oral ulcers indicate viral infection 9
Age-Related Presentation Variations
School-aged children (5-15 years) most commonly present with classic exudative pharyngitis, while only 20-30% show the complete classic picture 2, 8
Teenagers and adults often present with atypical findings making visual diagnosis more challenging 2, 9
Young children may show excoriated nares or purulent nasal discharge rather than classic tonsillar findings 1, 9
Critical Diagnostic Approach
Mandatory Testing Requirements
Clinical findings alone predict positive bacterial cultures only 80% of the time at best, making microbiological confirmation with throat culture or rapid antigen detection test (RADT) mandatory before prescribing antibiotics (Class I, Level of Evidence B) 1, 2, 8
Throat culture remains the gold standard, though it cannot differentiate true infection from asymptomatic carriage (15% of school-age children in winter/spring) 1
RADT provides rapid results but negative tests should be confirmed with throat culture in children and adolescents due to lower sensitivity 1
When to Test
Testing should be performed when clinical and epidemiological findings suggest bacterial pharyngitis (Class I, LOE B) 1
Testing is not routinely needed when findings strongly suggest viral etiology (conjunctivitis, coryza, cough, diarrhea) as the pretest probability is low (Class IIb, LOE B) 1
Treatment Approach Based on Etiology
Confirmed Group A Streptococcal Infection
Penicillin remains the first-line antibiotic despite bacteriologic failure rates up to 20%, with azithromycin (12 mg/kg once daily for 5 days) showing 95% bacteriologic eradication at Day 14 compared to 73% with penicillin V 10, 6
For penicillin-allergic patients, clindamycin is recommended over macrolides given the frequent role of Fusobacterium necrophorum in severe tonsillitis 5
Cephalosporins (all generations), amoxicillin-clavulanate, and clindamycin are more effective than penicillin in patients who failed previous penicillin therapy, likely due to eradication of beta-lactamase producing bacteria 6
Viral Tonsillitis
Treatment is supportive with analgesia and hydration only 4
Antibiotics should be withheld when throat culture or RADT is negative (Class I, LOE B) 1
Special Considerations for Fusobacterium necrophorum
Cultures from peritonsillar abscess aspirates should include selective F. necrophorum agar plates 5
Patients aged 15-24 years with severe acute tonsillitis warrant increased vigilance for incipient peritonsillar involvement 5
Common Pitfalls to Avoid
Do not assume exudates equal bacterial infection - viral infections frequently produce exudates that are clinically indistinguishable from bacterial causes 1, 2, 9
Do not rely on presence or absence of fever to diagnose bacterial pharyngitis, as fever is neither sensitive nor specific and leads to massive overtreatment when used as a criterion 8
Do not prescribe antibiotics based on clinical impression alone - experienced clinicians overestimate bacterial pharyngitis when relying on clinical findings without microbiological confirmation 8
Do not test asymptomatic household contacts of patients with streptococcal pharyngitis routinely 1
Do not perform routine flexible bronchoscopy in uncomplicated tonsillitis cases 1