What are the typical clinical features of acute pharyngitis and how can streptococcal (bacterial) pharyngitis be distinguished from viral pharyngitis?

Clinical Features of Acute Pharyngitis

Acute pharyngitis is predominantly viral, but Group A Streptococcus (GAS) is the only common cause requiring antibiotics—and clinical features alone cannot reliably distinguish bacterial from viral infection, making microbiological confirmation mandatory before treatment. 1, 2

Typical Clinical Presentation

Viral Pharyngitis Features

Viral agents cause the majority of acute pharyngitis cases and present with characteristic upper respiratory symptoms: 1, 2

• Cough, rhinorrhea (runny nose), hoarseness, and conjunctivitis strongly suggest viral etiology 1, 2, 3
• Discrete oral ulcers or ulcerative stomatitis indicate viral infection 2, 3
• Gradual onset of symptoms over 1-2 days 2
• Diarrhea may accompany viral pharyngitis 2
• Viral exanthem (characteristic rash) may be present 3

Common viral agents include adenovirus, rhinovirus, respiratory syncytial virus, parainfluenza virus, coxsackievirus, ECHO viruses, herpes simplex virus, and Epstein-Barr virus. 1, 2

Bacterial (GAS) Pharyngitis Features

GAS pharyngitis accounts for 20-30% of pediatric cases (ages 5-15 years) and only 5-15% of adult cases: 2, 4

• Sudden onset of severe sore throat is characteristic 1, 2, 5
• Fever (typically 101-104°F/38.3-40°C), though not always present 2, 6
• Pain on swallowing (odynophagia) 1, 2
• Tonsillopharyngeal erythema with or without patchy exudates 1, 2, 3
• Tender, enlarged anterior cervical lymph nodes 1, 2, 3, 7
• Palatal petechiae ("doughnut lesions") are highly suggestive when present 2, 3
• Beefy red, swollen uvula 1, 3
• Headache is common 1, 3, 5
• Nausea, vomiting, or abdominal pain, especially in children 1, 2, 3
• Chills and sweats may occur 8, 5
• Scarlatiniform rash may accompany infection 1

Critical caveat: None of these findings—individually or collectively—is specific enough to diagnose GAS pharyngitis without laboratory confirmation. 1, 2, 3

Key Distinguishing Algorithm

When to Suspect Viral (Do NOT Test for GAS)

If ANY of these viral features are present, testing for GAS is not recommended: 1, 2

• Cough
• Rhinorrhea/coryza
• Hoarseness
• Conjunctivitis
• Oral ulcers
• Viral rash

When to Test for GAS

Test when the patient has: 2

• Sudden-onset sore throat AND
• Fever AND
• Absence of all viral features listed above 2

Additional factors increasing GAS likelihood: 2

• Age 5-15 years (peak incidence)
• Winter/early spring presentation
• Close contact with documented GAS case
• Tender anterior cervical lymphadenopathy
• Tonsillar exudates

Diagnostic Testing Requirements

Microbiological confirmation is mandatory before prescribing antibiotics—even experienced clinicians cannot reliably distinguish GAS from viral pharyngitis clinically. 1, 2

• Rapid antigen detection test (RADT) should be performed first; a positive result is diagnostic and warrants immediate treatment 2, 7
• In children and adolescents, a negative RADT must be followed by throat culture due to lower sensitivity and the risk of rheumatic fever 2
• In adults, backup throat culture after negative RADT is optional given low rheumatic fever risk 2
• Throat culture on sheep-blood agar remains the gold standard (90-95% sensitivity, 24-48 hour turnaround) 2, 5

Common Pitfalls to Avoid

• Do not treat based on clinical impression alone—this leads to 50-70% unnecessary antibiotic use because viral causes predominate 2
• Do not assume all exudative pharyngitis is bacterial—viruses (especially adenovirus and EBV) frequently produce exudates 2
• Do not test children under 3 years unless specific risk factors exist (e.g., household contact with GAS), as GAS pharyngitis and rheumatic fever are rare in this age group 1, 2, 4
• Do not test or treat asymptomatic household contacts—positive results often represent carriage rather than infection 2, 4
• Do not rely on fever alone—fever is neither sensitive nor specific for GAS, and some confirmed cases present without significant fever 6
• Recognize that 10-20% of school-age children are asymptomatic GAS carriers—a positive test in a patient with predominantly viral symptoms may reflect carriage, not acute infection 2

Epidemiological Context

• Age: GAS pharyngitis primarily affects children 5-15 years; it is uncommon in children <3 years and accounts for only 5-15% of adult pharyngitis 1, 2, 4
• Season: Peak incidence occurs in winter and early spring (November-May) in temperate climates 1, 2
• Exposure: Recent close contact with a documented GAS case significantly increases likelihood 1, 2