What are the signs, symptoms, and etiology of bronchopneumonia in a healthy adult patient with no significant underlying medical conditions?

Bronchopneumonia: Signs, Symptoms, and Etiology

Clinical Presentation

Bronchopneumonia in healthy adults presents as an acute illness with cough as the primary symptom, accompanied by at least one additional lower respiratory tract finding including sputum production, dyspnea, wheeze, or chest discomfort, lasting 21 days or less. 1

Cardinal Symptoms

• Cough: The hallmark symptom, which may be productive with purulent (yellow-green) sputum or occasionally blood-tinged phlegm 2, 3, 4
• Fever: Temperature ≥38°C (100.4°F) persisting for more than 4 days strongly suggests pneumonia rather than simple bronchitis 1
• Dyspnea and tachypnea: Breathlessness with respiratory rate >24 breaths/min is a critical finding 1
• Pleuritic chest pain: Sharp, localized chest discomfort worsened by breathing 5

Key Physical Examination Findings

New focal chest signs are the most diagnostically significant findings and include: 1, 5, 6

• Crackles (rales): Present in approximately 81% of pneumonia patients, representing sudden opening of collapsed alveoli filled with inflammatory exudate 6
• Diminished breath sounds: Localized reduction in air movement due to consolidation 1, 6
• Bronchial breath sounds: Heard over areas of consolidation 1

Vital Sign Abnormalities

The combination of abnormal vital signs significantly increases pneumonia likelihood: 1, 7

• Tachycardia: Heart rate >100 beats/min 1
• Tachypnea: Respiratory rate >24 breaths/min 1, 7
• Fever: Temperature ≥38°C 1, 7

The absence of all four findings (tachycardia, tachypnea, fever, and focal chest signs) significantly reduces pneumonia likelihood. 5

Distinguishing Features from Acute Bronchitis

The absence of upper respiratory symptoms (particularly runny nose) combined with breathlessness, crackles, and diminished breath sounds strongly favors pneumonia over bronchitis. 1, 6

Diagnostic Approach

Clinical Suspicion Criteria

Suspect pneumonia when a patient presents with acute cough PLUS at least one of the following: 1

• New focal chest signs on examination
• Fever persisting >4 days
• Dyspnea or tachypnea

Radiographic Confirmation

Chest radiography is required to confirm the diagnosis, as physical examination alone is neither sensitive nor specific. 1, 5 However, recognize that chest X-ray may be normal in up to 64% of early pneumonia cases, with typical appearances present in only 36% initially 5. If clinical suspicion remains high despite negative initial imaging, repeat chest radiography in 24-48 hours as radiographic changes develop over time 5.

Laboratory Testing

C-reactive protein (CRP) significantly improves diagnostic accuracy when combined with clinical findings: 1, 6

• CRP >30 mg/L: Increases pneumonia likelihood substantially
• **CRP <10 mg/L**: Makes pneumonia very unlikely if symptoms present >24 hours
• CRP 10-50 mg/L without dyspnea and daily fever: Decreases pneumonia likelihood

Procalcitonin adds no significant diagnostic value beyond symptoms, signs, and CRP and is not recommended. 1, 6

Etiology

Bacterial Pathogens

The most common bacterial causes of community-acquired pneumonia in healthy adults include: 1

• Streptococcus pneumoniae: The predominant bacterial pathogen
• Haemophilus influenzae: Common in patients with underlying lung disease
• Mycoplasma pneumoniae: Causes atypical pneumonia with segmental/subsegmental infiltrates, often presenting with headache, malaise, and normal white blood cell count 8
• Legionella pneumophila: Consider with relevant exposure history
• Bordetella pertussis: Increasingly recognized cause

Emerging Pathogens

PVL-producing Staphylococcus aureus has emerged as a cause of severe pneumonia but remains uncommon. 1

Polymicrobial and Viral Infections

Polymicrobial infections, including viral co-infections, are increasingly recognized as contributing to pneumonia pathogenesis. 1 However, there has been no major change in causative pathogens overall 1.

Common Pitfalls

Atypical Presentations

Mycoplasma pneumoniae can present atypically with lethargy, dyspnea, and 1-4 week history of shortness of breath WITHOUT cough or fever, associated with diffuse reticulonodular or interstitial infiltrates rather than focal consolidation. 8 This contrasts with the typical segmental pattern.

Elderly Patients

Maintain high suspicion in elderly patients, as they frequently present with absent or altered respiratory and non-respiratory symptoms despite radiographic pneumonia. 5, 7

Misleading Physical Findings

Wheezing, prolonged expirations, or rhonchi alone do NOT significantly increase pneumonia likelihood and may mislead toward alternative diagnoses like asthma or bronchitis. 6

Early Radiographic Findings

Dehydration can mask infiltrates that appear later with rehydration, potentially causing false-negative initial chest X-rays. 5