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Tonsillitis What about using of Cotrimoxazol (trimethoprim/sulfamethoxazol) and tetracyclines in bacterial tonsillitis? How to confirm the clinical diagnosis of Streptococcal Tonsillitis in symptomatic patients? Is determination of ASL-O values indicated to establish the diagnosis of Streptococcal Tonsillitis? Explain according to WHO with appropriate doses

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PMID: 41343363

1. Co-trimoxazole and tetracyclines in bacterial tonsillitis

Do not use co-trimoxazole (trimethoprim-sulfamethoxazole) or tetracyclines to treat confirmed or suspected group A streptococcal (GAS, Streptococcus pyogenes) tonsillitis/pharyngitis.
  • Co-trimoxazole: unreliable for eradication of GAS from the pharynx and therefore should not be used to prevent acute rheumatic fever. WHO-associated standard treatment guidance specifically states that co-trimoxazole is unsuitable for primary streptococcal throat infection.
  • Tetracyclines, including doxycycline: GAS resistance is common and variable. They are not recommended for GAS pharyngitis/tonsillitis.
  • These agents may have roles in other infections, but not as treatment for presumed GAS tonsillitis.

2. Confirming streptococcal tonsillitis in a symptomatic patient

Clinical features help select patients for testing, but clinical examination alone cannot confirm GAS. Viral pharyngitis is much more common.

Clinical likelihood assessment: Centor criteria

Give 1 point for each:
  1. Fever >38°C
  2. Absence of cough
  3. Tender anterior cervical lymph nodes
  4. Tonsillar swelling or exudate
WHO’s antibiotic-book approach estimates the probability of GAS approximately as:
Centor scoreApproximate probability of GASAction
01-2.5%Symptomatic care, no testing/antibiotics
15-10%Usually symptomatic care
211-17%Test with RADT or throat culture
328-35%Test, or consider empiric treatment in high-rheumatic-fever settings if testing is unavailable
≥451-53%Test if available; empiric treatment may be appropriate in high-risk endemic settings
Features that support GAS include sudden sore throat, fever, painful swallowing, tonsillar exudate, palatal petechiae, tender anterior cervical lymphadenopathy, scarlet-fever rash, and no cough. Features such as cough, coryza/rhinorrhea, hoarseness, oral ulcers, or conjunctivitis favor a viral cause.
A recent guideline review confirms that clinician judgement alone is unreliable and that a clinical score is mainly useful to identify low-risk patients who do not need testing (IDSA guideline review).

Tests that establish the diagnosis

  1. Rapid antigen detection test (RADT) on a throat swab
    • A positive RADT confirms GAS because specificity is high.
    • Obtain a proper specimen by swabbing both tonsils/tonsillar fossae and the posterior pharynx, avoiding the tongue and cheeks.
  2. Throat culture
    • This is the reference standard, typically culture on sheep blood agar.
    • In children and adolescents, a negative RADT should generally be backed up by throat culture, because RADT sensitivity is imperfect.
    • In adults, backup culture after a negative RADT is usually unnecessary because acute rheumatic fever is uncommon.
  3. Molecular assay/NAAT, where available
    • Highly sensitive and specific, and may replace culture depending on the local test and policy.
Do not routinely test patients with clear viral features. The medical text reference describes throat culture as the diagnostic gold standard, with reported sensitivity of about 96% (Textbook of Family Medicine, p. 1512).

3. Is ASL-O/ASO useful to diagnose acute streptococcal tonsillitis?

No. ASL-O, also called ASO titre, is not indicated to establish the diagnosis of acute streptococcal tonsillitis.
Why not:
  • ASO measures antibodies to streptolysin O, not the organism in the throat.
  • It rises only about 3-5 weeks after GAS pharyngitis and may remain elevated for months.
  • A raised result can reflect a previous infection and does not prove that the current sore throat is caused by GAS.
  • A normal early ASO does not exclude current GAS tonsillitis.

When ASO is useful

ASO, ideally interpreted with the clinical picture and sometimes paired titres or anti-DNase B, is useful as evidence of a preceding GAS infection when evaluating possible post-streptococcal complications, especially:
  • Acute rheumatic fever
  • Post-streptococcal glomerulonephritis
WHO technical material also describes ASO as an unreliable indicator of an acute throat infection.

4. WHO-based treatment doses for GAS pharyngitis/tonsillitis

Antibiotics are for confirmed GAS, or for selected high-probability patients in settings with high rheumatic-fever risk where diagnostic testing is unavailable. They are not indicated for routine viral tonsillitis.

First-choice oral therapy

PatientPhenoxymethylpenicillin (penicillin V)Alternative: amoxicillinDuration
Adults500 mg orally every 6 hours500 mg orally every 8 hours10 days
Children15 mg/kg per dose orally every 6 hoursLocal paediatric guideline dosing should be followed. A widely used regimen is 50 mg/kg once daily, maximum 1 g/day, or 25 mg/kg twice daily, maximum 500 mg/dose10 days
WHO’s Essential Medicines Antibiotic Book lists phenoxymethylpenicillin for pharyngitis as 500 mg every 6 hours in adults and 15 mg/kg per dose every 6 hours in children (WHO antibiotic book).

When adherence to 10 days of oral treatment is doubtful

Benzathine benzylpenicillin G, intramuscular, single dose:
  • <27 kg: 600,000 units IM once
  • ≥27 kg: 1.2 million units IM once
This is a standard effective regimen for GAS eradication and rheumatic-fever prevention, provided there is no history of immediate severe penicillin allergy.

Penicillin allergy

The alternative depends on the type of allergy and local macrolide-resistance patterns:
  • Non-immediate, non-anaphylactic penicillin allergy: a first-generation cephalosporin may be used if considered safe by the clinician.
  • Immediate/anaphylactic beta-lactam allergy: a macrolide such as azithromycin, clarithromycin, or erythromycin can be used, following local guidelines and susceptibility patterns.
Do not substitute co-trimoxazole or tetracycline/doxycycline.

Practical summary

  • Diagnose GAS tonsillitis with a throat RADT or throat culture, not symptoms alone.
  • Use Centor criteria to decide whom to test, not as definitive confirmation.
  • ASO is not an acute diagnostic test.
  • Treat confirmed/high-probability GAS with penicillin V or amoxicillin for 10 days, or single-dose IM benzathine penicillin when appropriate.
  • Avoid co-trimoxazole and tetracyclines for GAS tonsillitis.

In short

  • Do not use co-trimoxazole or tetracyclines for streptococcal tonsillitis. They do not reliably eradicate group A streptococcus and do not prevent rheumatic fever.
  • Diagnosis: symptoms suggest GAS, but do not confirm it. Use Centor criteria: fever >38°C, no cough, tender anterior cervical nodes, tonsillar exudate. Confirm with a rapid strep test (RADT) or throat culture.
    • Positive RADT: confirms GAS.
    • Negative RADT in children: do throat culture.
  • ASO/ASL-O titre: not useful for acute diagnosis. It rises weeks later. Use it only when investigating post-streptococcal complications, such as rheumatic fever or glomerulonephritis.
  • WHO-based treatment for confirmed/high-probability GAS:
    • Adults: Penicillin V 500 mg orally every 6 hours for 10 days, or amoxicillin 500 mg orally every 8 hours for 10 days.
    • Children: Penicillin V 15 mg/kg per dose orally every 6 hours for 10 days.
    • If oral adherence is difficult: benzathine penicillin G IM once:
      • <27 kg: 600,000 units
      • ≥27 kg: 1.2 million units
  • For true severe penicillin allergy, use a locally recommended macrolide, considering local resistance.
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