What are the signs and symptoms of community-acquired pneumonia (CAP)?

Signs and Symptoms of Community-Acquired Pneumonia

Community-acquired pneumonia should be suspected when a patient presents with cough plus at least one other lower respiratory tract symptom (sputum production, dyspnea, wheeze, or chest discomfort) along with fever, and this diagnosis must be confirmed by demonstrating a new infiltrate on chest radiograph or other imaging. 1

Core Respiratory Symptoms

The diagnosis requires at least two of the following respiratory symptoms to be present: 1

• New or worsening cough (with or without sputum production, or change in sputum color in patients with chronic cough) 1
• Dyspnea or tachypnea (shortness of breath or increased respiratory rate) 1
• Chest discomfort or pleuritic chest pain 1
• Sputum production (new onset or increased) 1

Systemic Signs

Fever is a cardinal feature, though it may be absent in elderly or immunocompromised patients: 1

• Fever (temperature >38°C) or hypothermia (temperature <36°C) 1, 2
• Rigors and sweats 1
• Hypothermia carries an ominous prognosis when present 1

Physical Examination Findings

Auscultatory findings are important but less sensitive and specific than chest radiography: 1, 3

• Abnormal breath sounds (altered or bronchial breath sounds) 1
• Crackles or localized rales 1
• Egophony (positive likelihood ratio of 6.17, making it highly suggestive when present) 4
• Dullness to percussion (positive likelihood ratio of 2.62) 4
• Tachypnea (respiratory rate ≥30 breaths/min suggests severe disease) 1

Nonspecific Systemic Symptoms

Most patients also present with nonspecific symptoms that accompany the respiratory findings: 1

• Fatigue and malaise 1
• Myalgias 1
• Headache 1
• Anorexia 1
• Abdominal pain 1

Atypical Presentations in Elderly Patients

In patients with advanced age or inadequate immune response, pneumonia frequently presents without typical respiratory symptoms: 1

• Confusion or altered mental status 1
• Failure to thrive 1
• Worsening of underlying chronic illness 1
• Falls 1
• Fever may be absent, but tachypnea is usually present along with abnormal chest examination 1

Clinical Assessment Tools

An abnormal overall clinical impression suggesting CAP has the highest diagnostic value (positive likelihood ratio of 6.32 and area under the curve of 0.741), making gestalt clinical judgment particularly important. 4

The absence of abnormal vital signs substantially decreases the probability of CAP (negative likelihood ratio of 0.25), making pneumonia unlikely when vital signs are completely normal. 4

Essential Diagnostic Confirmation

Pulse oximetry should be performed on all patients to screen for hypoxemia, which may be present even without obvious clinical signs. 1

Chest radiography is required to establish the diagnosis and differentiate CAP from acute bronchitis and other causes of acute cough illness, as clinical features alone cannot reliably diagnose pneumonia with adequate sensitivity and specificity. 1, 3

Common Pitfalls

Do not rely on the traditional "typical" versus "atypical" pneumonia classification, as pathogens like Legionella can cause a wide spectrum of illness, making this distinction clinically unhelpful. 3

Temperature measurement is more valuable than patient-reported fever (positive likelihood ratio of 2.52 for measured temperature), so always obtain objective vital signs rather than relying on history alone. 4