How can I differentiate acute otitis media, viral pharyngitis, and streptococcal pharyngitis?

Differentiating Ear Infection, Sore Throat, and Strep Throat

Acute otitis media (AOM) requires visual confirmation of middle ear inflammation with a bulging tympanic membrane, viral pharyngitis presents with gradual onset and respiratory symptoms like cough and runny nose, while streptococcal pharyngitis shows abrupt onset of severe sore throat with fever and tonsillar exudate but WITHOUT cough or nasal symptoms.

Acute Otitis Media (Ear Infection)

Diagnostic Criteria

• AOM is a visual diagnosis requiring pneumatic otoscopy—you cannot diagnose it on history alone 1, 2
• Look for a bulging tympanic membrane with middle ear effusion and signs of acute inflammation 1
• The pneumatic otoscope is the standard diagnostic tool; proficiency in distinguishing normal tympanic membranes from AOM is essential 2

Key Clinical Features

• Most common bacterial pathogens are Haemophilus influenzae (44%), Streptococcus pneumoniae (28%), and Moraxella catarrhalis 1
• Bacteria are present in 84-96% of properly diagnosed AOM cases 1
• Often follows viral upper respiratory infection with eustachian tube dysfunction 1

Viral Pharyngitis (Sore Throat)

Distinguishing Features

• Presence of cough, runny nose (coryza), conjunctivitis, or diarrhea strongly suggests viral etiology 3
• Gradual symptom onset 3
• Accounts for the majority of pharyngitis cases in both children and adults 2, 4

Clinical Approach

• Viruses are the predominant cause of acute pharyngitis 5, 6
• Testing for streptococcus is NOT indicated when viral symptoms (cough, rhinorrhea) are present 3
• Treatment focuses on symptom management only—antibiotics are inappropriate 5

Streptococcal Pharyngitis (Strep Throat)

Diagnostic Criteria Using Modified Centor Score

Award 1 point for each:

• Fever (temperature >38°C/100.4°F) 3, 7
• Tonsillar exudate 3, 7
• Tender anterior cervical lymphadenopathy 3, 7
• Absence of cough (subtract 1 point if cough present) 3, 7
• Age 3-15 years (add 1 point); age >45 years (subtract 1 point) 7

Testing Strategy

• Score 0-1: No testing or antibiotics needed 7
• Score 2-3: Perform rapid antigen detection test (RADT) 1, 7
• Score 4-5: RADT or empiric treatment acceptable 7
• If RADT is negative in children/adolescents, follow with throat culture (gold standard) 1, 3
• In adults, negative RADT does not require culture confirmation 1

Clinical Presentation

• Abrupt onset of intense sore throat 3
• Fever, chills, malaise, headache 3
• Pharyngeal or tonsillar exudate 3
• Absence of cough, coryza, conjunctivitis, and diarrhea 3

Treatment When Confirmed

• Penicillin V or amoxicillin for 10 days (first-line) 1, 7
• First-generation cephalosporins for non-anaphylactic penicillin allergy 7
• Avoid azithromycin/clarithromycin due to significant resistance in many U.S. regions 7

Critical Pitfalls to Avoid

Common Diagnostic Errors

• Do not diagnose AOM without otoscopic visualization—history alone is insufficient 2
• Do not test for strep throat in patients with cough or rhinorrhea—these symptoms indicate viral etiology 3
• Up to 15% of children are streptococcal carriers; indiscriminate testing leads to inappropriate antibiotic use 2
• Only treat positive tests, not clinical suspicion alone (except very high Centor scores) 1, 7

Reassessment Triggers

• For AOM: Reassess if symptoms worsen or fail to improve within 48-72 hours of antibiotic initiation 1
• For strep pharyngitis: Reevaluate if symptoms worsen after starting antibiotics or persist beyond 5 days of treatment 7