Approach to sore throat: Centor and McIsaac

What it is

Acute sore throat is one of the commonest reasons to see a primary care doctor. Most cases are viral and settle on their own; group A beta-haemolytic streptococcus is the commonest bacterial cause and the only common one that benefits from an antibiotic. The challenge is to avoid unnecessary antibiotics without missing streptococcus or the serious conditions that mimic a simple pharyngitis: peritonsillar abscess, epiglottitis, deep neck infection and diphtheria. Colombia has no MinSalud Clinical Practice Guideline specific to pharyngotonsillitis; the Ministry and IETS published guidance on rational antibiotic use for immunocompetent adults in primary care, based on the Centor and FeverPAIN scores.

Key questions in the history

• Is there cough, runny nose, hoarseness or conjunctivitis? These point to a viral cause.
• Did it start suddenly with high fever? That points to streptococcus.
• Can the patient swallow saliva and open the mouth fully? Drooling and trismus suggest abscess or epiglottitis.
• Any past rheumatic fever, or cases of strep throat at home or at school?
• Is the patient vaccinated against diphtheria? Any contact with cases?
• Is the patient immunosuppressed or taking drugs that can cause neutropenia?

Causes and classification

• Viral (most cases): common cold (rhinovirus, coronavirus), adenovirus, influenza, Epstein-Barr virus, enteroviruses.
• Bacterial: group A beta-haemolytic streptococcus (the commonest); others: group C and G streptococci, gonococcus and, rarely, Corynebacterium diphtheriae.
• Suppurative complications of streptococcus: peritonsillar abscess, retropharyngeal abscess, cervical lymphadenitis and mastoiditis.
• Non-suppurative complications: acute rheumatic fever and post-streptococcal glomerulonephritis.
• Dangerous mimics: epiglottitis, deep neck infection and diphtheria.
• Non-infectious: reflux and irritants such as tobacco; if pain persists or is one-sided, an oropharyngeal tumour.

Step-by-step approach

1. First rule out airway compromise: stridor, drooling, inability to swallow saliva or a tripod position.
2. Look for viral symptoms (cough, runny nose, hoarseness, conjunctivitis, ulcers): if present, it is viral and needs no tests.
3. Apply Centor in adults or McIsaac, which includes age and is used more in children, and add up the points.
4. Score 0–1: symptomatic care, no test and no antibiotic.
5. Score 2–3: rapid antigen test or throat culture; antibiotic only if positive.
6. Score 4 or more: rapid test; if no test is available, empirical antibiotic.
7. In children over 3 years with a negative rapid test, the CDC recommends a backup culture; adults do not need one.
8. Check for abscess: deviated uvula, bulging soft palate, trismus or a muffled voice.
9. Explain the expected course and when to come back: worsening, trouble swallowing or trouble breathing.

Differential diagnosis of acute sore throat

Red flags

• Stridor, breathing difficulty or drooling: possible epiglottitis or airway obstruction; a life-threatening emergency.
• Trismus, muffled voice and deviated uvula: peritonsillar abscess.
• Neck pain and stiffness, neck swelling or persistent fever: deep neck infection.
• Adherent greyish pseudomembrane and bull neck in an unvaccinated person: diphtheria.
• Looks unwell, dehydration or signs of shock.
• Known immunosuppression or neutropenia.
• Sore throat lasting more than 2 weeks, one-sided, or with earache and a neck node in an adult smoker: rule out cancer.

Next step / Initial management

• Tests: rapid antigen test or throat culture only if Centor or McIsaac is 2 or more; antistreptolysin O does not diagnose the acute illness.
• Symptomatic: paracetamol first line, or ibuprofen; avoid routine corticosteroids (MinSalud-IETS guidance).
• Confirmed streptococcus, or a high score with no test: penicillin V or amoxicillin, full course; alternative, benzathine penicillin; if allergic, cefalexin, azithromycin or clindamycin (no cephalosporins after an immediate-type reaction).
• Give no antibiotic if mononucleosis is suspected; do not repeat the swab after treatment; if no better at 48–72 hours, reassess and consider second line.
• Refer urgently, the same day, for stridor, drooling, trismus, suspected abscess, deep neck infection or diphtheria.
• Routine referral to ENT for recurrent bacterial pharyngotonsillitis (3 or more episodes a year).

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Educational content; it does not replace a medical assessment and is not a clinical instruction. For a real case, follow current guidelines and specialist advice.

Sources: Guidance for a rational antibiotic use strategy in bacterial pharyngotonsillitis in immunocompetent adults, for general practitioners in primary care (Colombia) (Ministerio de Salud y Protección Social de Colombia; Instituto de Evaluación Tecnológica en Salud (IETS), 2020); Clinical Guidance for Group A Streptococcal Pharyngitis (Centers for Disease Control and Prevention (CDC), 2025); Clinical Features of Diphtheria (Centers for Disease Control and Prevention (CDC), 2026).

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