What are the causes of pharyngitis and does it require antibiotics?

Pharyngitis: Causes and Antibiotic Indications

Most pharyngitis is viral and does not require antibiotics; antibiotics are justified only when Group A Streptococcus (GAS) is confirmed by laboratory testing. 1

Causes of Pharyngitis

Viral Etiologies (Majority of Cases)

• Respiratory viruses account for the majority of pharyngitis cases, including adenovirus, influenza, parainfluenza, rhinovirus, and respiratory syncytial virus 2
• Epstein-Barr virus causes infectious mononucleosis with pharyngitis, generalized lymphadenopathy, and splenomegaly 2
• Clinical clues suggesting viral etiology include conjunctivitis, coryza (runny nose), cough, and diarrhea 2

Bacterial Etiologies

• Group A β-hemolytic Streptococcus (GAS) is the only common bacterial cause requiring routine antibiotic treatment 1, 2
• GAS accounts for 25-40% of pharyngitis cases in children and 10-25% in adults, with peak incidence between ages 5-15 years 1
• Rare bacterial causes include Corynebacterium diphtheriae, Neisseria gonorrhoeae, and anaerobic organisms, but these require special consideration beyond routine management 1, 2

When Antibiotics Are Needed

The Critical Diagnostic Rule

Clinical symptoms alone cannot reliably distinguish bacterial from viral pharyngitis—laboratory confirmation is mandatory before prescribing antibiotics. 1, 2

Laboratory Testing Algorithm

For Adults:

• Perform rapid antigen detection test (RADT) when GAS is suspected 1
• A positive RADT confirms GAS and justifies antibiotics 1
• A negative RADT is sufficient to rule out GAS—no backup culture needed, withhold antibiotics 1, 3
• The specificity of RADT is ≥95% and sensitivity is 80-90% 3

For Children and Adolescents:

• Perform RADT when GAS is suspected 1
• A positive RADT confirms GAS and justifies antibiotics 1
• A negative RADT must be confirmed with throat culture before withholding antibiotics 1, 3
• This backup culture is necessary because children have higher GAS prevalence (20-30%) and higher risk of acute rheumatic fever 3
• Children under 3 years should generally not be tested, as GAS is rarely involved in this age group 1

When to Withhold Antibiotics

Antibiotics should be withheld in the following situations:

• Negative RADT in adults (no further testing needed) 1, 3
• Negative RADT and negative throat culture in children 1, 3
• Presence of viral symptoms (cough, rhinorrhea, conjunctivitis, diarrhea) 2
• Antibiotics have not proved effective in nonstreptococcal pharyngitis 1

Rationale for Selective Antibiotic Use

Benefits of Treating Confirmed GAS

• Rapid disappearance of symptoms (Grade A evidence) 1
• Prevention of acute rheumatic fever (Grade A evidence for penicillin) 1
• Eradication or decreased dissemination of GAS (Grade A evidence) 1
• Prevention of suppurative complications such as peritonsillar abscess and cervical lymphadenitis 1

Why Antibiotics Are Not Justified Without Confirmation

• Even untreated GAS pharyngitis generally improves within 3-4 days 1
• The current risk for acute rheumatic fever is extremely low in industrialized countries (though remains high in developing countries) 1
• The incidence of suppurative complications is low (1%) in industrialized countries, independent of antibiotic therapy 1
• Antibiotics do not prevent post-streptococcal glomerulonephritis 1
• Antibiotics shorten sore throat duration by only 1-2 days, with number needed to treat of 6 at 3 days 3

Recommended Antibiotic When GAS Is Confirmed

Penicillin or amoxicillin for 10 days remains the treatment of choice due to proven efficacy, safety, narrow spectrum, and low cost 1

For penicillin-allergic patients:

• First-generation cephalosporin for 10 days (if not anaphylactically sensitive) 1
• Clindamycin or clarithromycin for 10 days 1
• Azithromycin for 5 days 1

Management of Negative Test Results

Provide symptomatic treatment only:

• Analgesics/antipyretics such as acetaminophen or ibuprofen for symptom relief 1, 3
• Throat lozenges 3
• Reassurance that symptoms typically resolve in less than 1 week 3
• Avoid aspirin in children 1

Common Pitfalls to Avoid

• Never prescribe antibiotics based on clinical appearance alone (white patches, exudate, tonsillar swelling)—these overlap too broadly between viral and bacterial causes 3, 2
• Do not test or treat asymptomatic household contacts, even with history of recurrent infections 1, 3
• Do not perform follow-up testing after successful treatment in asymptomatic patients—this may simply reflect carrier status 1, 3
• Do not switch antibiotics without microbiological indication, as this increases adverse effects without clinical benefit 3

Special High-Risk Situations

Consider culture confirmation of negative RADT in these rare circumstances:

• Individual history of acute rheumatic fever 1
• Age 5-25 years with poor social/hygienic conditions or closed institutional settings 1
• History of recurring GAS pharyngitis 1
• Recent stay in streptococcal-endemic regions (Africa, West Indies, developing countries) 1

In these high-risk contexts, if culture is positive after negative RADT, antibiotic therapy is justified 1