What is the best course of treatment for a patient presenting with symptoms of a respiratory illness, such as sore throat, fever, and cough, to differentiate between strep throat and influenza (flu)?

Differentiating Strep Throat from Influenza in Respiratory Illness

For patients presenting with respiratory symptoms, use clinical criteria to distinguish between strep pharyngitis and influenza: strep throat presents with sore throat, fever, tonsillar exudates, and tender cervical lymph nodes WITHOUT cough, while influenza presents with fever, cough, myalgia, and acute onset—the presence or absence of cough is the key discriminating feature. 1, 2

Clinical Approach to Differentiation

Influenza-Like Illness (ILI) Characteristics

Influenza is defined by fever with acute onset plus one or more of: headache, myalgia, cough, and sore throat. 1

Key features that suggest influenza:

• Fever (38-40°C) with acute onset 2
• Cough present in ~85% of cases 1, 2
• Myalgia affecting back and limbs (~53% of cases) 2
• Headache (~65%) 1
• The three-fold combination of fever, cough, and acute onset is most predictive 1, 2

Strep Pharyngitis Characteristics

Use the modified Centor criteria to assess likelihood of Group A Streptococcus: 1

Criteria include:

• Fever by history 1
• Tonsillar exudates 1
• Tender anterior cervical adenopathy 1
• Absence of cough 1

Patients meeting fewer than 3 Centor criteria do not need testing for strep. 1

Additional features favoring strep throat:

• Persistent fever, rigors, scarlatiniform rash, palatal petechiae, swollen tonsils 1
• Symptoms suggesting viral illness (cough, nasal congestion, conjunctivitis, hoarseness, diarrhea, oropharyngeal ulcers/vesicles) make strep unlikely 1

Diagnostic Algorithm

Step 1: Assess for Cough

• If prominent cough is present with fever and myalgia → suspect influenza 1, 2
• If sore throat without cough → consider strep pharyngitis 1

Step 2: Apply Clinical Scoring

For sore throat presentations:

• Score using Centor criteria 1
• ≥3 criteria → perform rapid antigen detection test or throat culture for Group A Streptococcus 1
• <3 criteria → no testing needed, likely viral 1

For ILI presentations:

• Fever + cough + acute onset during influenza season → high likelihood of influenza 1, 2
• Predictive value increases when influenza is circulating in the community 2

Step 3: Testing Decisions

For suspected strep pharyngitis (≥3 Centor criteria):

• Perform rapid antigen detection test or throat culture 1
• Do not test patients with viral symptoms (cough, nasal congestion, conjunctivitis) 1

For suspected influenza:

• Clinical diagnosis is sufficient during influenza season when virus is circulating locally 1, 2
• Laboratory confirmation may be considered but is not required for treatment decisions in typical cases 1

Treatment Implications

Strep Pharyngitis

• Antibiotics with narrow spectrum are appropriate only for confirmed Group A Streptococcus 3
• Do not prescribe antibiotics for viral pharyngitis 1

Influenza

• Most cases of acute bronchitis and ILI are viral and do not require antibiotics 1
• Antibiotics should not be initiated unless pneumonia is suspected 1
• Purulent sputum does not indicate bacterial infection requiring antibiotics 1

Critical Pitfalls to Avoid

Do not prescribe antibiotics based on purulent sputum alone—purulence results from inflammatory cells and occurs with both viral and bacterial infections. 1

Do not assume all sore throats are strep—most pharyngitis is viral (rhinovirus, coronavirus, adenovirus, influenza). 1

Reassess if fever persists beyond 3-4 days, as this may indicate bacterial superinfection or pneumonia requiring different management. 1, 4

Consider pneumonia if patient has new focal chest signs, dyspnea/tachypnea, or fever >4 days. 1