What focused history and physical examination should be performed for a patient presenting with influenza (flu)?

Focused History and Physical Examination for Influenza

For patients presenting with suspected influenza, focus your history on identifying acute onset fever (>38°C), cough, and systemic symptoms (myalgias, chills/sweats, headache), while your physical examination should prioritize vital signs—particularly temperature, respiratory rate, blood pressure, oxygen saturation—and respiratory assessment to identify complications requiring escalation of care.

History Taking

Core Diagnostic Features

The most useful historical elements for identifying influenza include 1:

• Fever >38°C (subjective or documented)
• Acute onset (symptoms <48-72 hours)
• Respiratory symptoms: Cough, sore throat, nasal congestion
• Systemic symptoms: Myalgias, chills/sweats, headache, fatigue

Key diagnostic combinations that increase likelihood of influenza 2:

• In patients ≥60 years: Fever + cough + acute onset (LR 5.4)
• Fever + cough alone (LR 5.0)
• Rigors when present (LR 7.2) 3
• Sweating (LR 3.0) 3

Important Caveats

• Individual symptoms have limited diagnostic value 3, 2. No single symptom reliably confirms or excludes influenza
• The absence of fever (LR 0.40), cough (LR 0.42), or nasal congestion (LR 0.49) makes influenza less likely 2
• Immunocompromised and very elderly patients may not mount adequate fever responses 1

Risk Stratification History

Document factors indicating high risk for severe disease 1:

• Age >65 years
• Chronic lung disease (COPD, asthma)
• Cardiovascular disease
• Diabetes mellitus
• Immunosuppression
• Pregnancy
• Obesity
• Chronic renal or liver disease

Timing and Treatment Window

• Duration of symptoms (critical for antiviral eligibility—must be ≤48 hours) 1
• Vaccination status for current season
• Exposure history to confirmed influenza cases

Physical Examination

Vital Signs (Priority Assessment)

Monitor and document 1:

• Temperature (>37.8°C indicates instability)
• Respiratory rate (>24-30/min indicates severity)
• Heart rate (>100/min indicates instability)
• Blood pressure (SBP <90 mmHg or DBP <60 mmHg indicates severity)
• Oxygen saturation (<90-92% requires intervention)
• Mental status (confusion indicates severity)

Respiratory Examination

Focus on identifying complications 1:

• Auscultation: Crackles, consolidation, or decreased breath sounds suggest pneumonia
• Work of breathing: Tachypnea, accessory muscle use, inability to speak in full sentences
• Chest pain or respiratory distress (more common with influenza than other respiratory infections) 4

General Assessment

• Hydration status: Assess for volume depletion 1
• Functional status: Ability to cope with daily activities, confinement to bed (absence decreases likelihood of influenza) 3

Severity Assessment Using CURB-65

Apply CURB-65 scoring if pneumonia suspected 1:

• Confusion (Mental Test Score <8)
• Urea >7 mmol/L
• Respiratory rate ≥30/min
• Blood pressure (SBP <90 or DBP ≤60 mmHg)
• Age ≥65 years

Score interpretation:

• 0-1: Likely suitable for outpatient management
• 2: Consider hospital admission
• ≥3: Manage as severe pneumonia in hospital
• Bilateral lung infiltrates on imaging = severe regardless of score 1

Clinical Decision Algorithm

1. Document fever + respiratory symptoms + systemic symptoms → Influenza-like illness (ILI)
2. Assess symptom duration → If ≤48 hours, patient eligible for antivirals
3. Calculate CURB-65 if lower respiratory symptoms present
4. Identify high-risk features → Determines treatment intensity
5. Check oxygen saturation → If <92%, requires hospital assessment

Common Pitfalls to Avoid

• Don't rely on clinical diagnosis alone during non-epidemic periods—influenza prevalence dramatically affects predictive value 2
• Don't dismiss influenza in afebrile elderly or immunocompromised patients 1
• Don't wait for diagnostic confirmation to start antivirals in severe cases 1—treatment should begin empirically if high clinical suspicion
• Don't overlook cardiac complications—assess for arrhythmias and heart failure exacerbation 1
• Sneezing makes influenza LESS likely in older patients (LR 0.47) 2

Diagnostic Testing Considerations

While not strictly H&P, testing strategy informs clinical assessment 1:

• Chest X-ray recommended for all hospitalized patients with suspected influenza
• Rapid antigen testing useful during epidemic periods for high-risk patients
• Clinical diagnosis sufficiently accurate during documented community outbreaks 2

The evidence consistently shows that clinical findings identify influenza-like illness but cannot definitively confirm or exclude influenza 2. Your H&P should therefore focus on severity assessment and risk stratification rather than definitive diagnosis, using epidemiologic context (is influenza circulating locally?) to guide empiric management decisions.