Clinical features

Typical pneumonia

Typical pneumonia is characterized by a sudden onset of symptoms caused by lobar infiltration.

• Severe malaise
• High fever and chills
• Productive cough with purulent sputum (yellow-greenish)
  • Crackles and bronchial breath sounds on auscultation
  • Decreased breath sounds
  • Enhanced bronchophony, egophony, and tactile fremitus
  • Dullness on percussion
• Tachypnea and dyspnea (nasal flaring, thoracic retractions)

Suspect bacterial pneumonia in immunocompromised patients with acute high fever and pleural effusion.

Atypical pneumonia

Atypical pneumonia typically has an indolent course (slow onset) and commonly manifests with extrapulmonary symptoms.

• Nonproductive, dry cough
• Dyspnea
• Auscultation often unremarkable
• Common extrapulmonary features include fatigue, headaches, sore throat, myalgias, and malaise.

This classification does not have a major impact on patient management because it is not always possible to clearly distinguish between typical and atypical pneumonia.

Pathogen-specific pneumonia

Mycoplasma pneumonia

Microbiology

• Incomplete/absent cell wall (not visible on gram stain)
• Bacterial membrane stabilized by cholesterol (obtained from host cell)
• Grows on Eaton agar → “fried egg” appearance

Epidemiology

• One of the most common causes of atypical pneumonia
• More common in school-aged children and adolescents
• Outbreaks most commonly occur in schools, colleges, prisons, and military facilities.

Clinical features

• Generalized papular rash
• Erythema multiforme
• Pneumonia > Atypical pneumonia

Diagnostics

• Subclinical hemolytic anemia: associated with elevated cold agglutinin titers (IgM)
• Interstitial pneumonia, often with a reticulonodular pattern on chest x-ray
• Chest x-ray can show extensive pulmonary involvement in patients with mild pneumonia.

Aspiration pneumonia

Definitions

• Aspiration pneumonia: a type of pneumonia that occurs as a result of upper airway or stomach microbes (anaerobes) aspiration
• Aspiration pneumonitis
  • Aspiration of gastric acid that initially causes tracheobronchitis, with rapid progression to chemical pneumonitis
  • May cause ARDS in extreme cases

Clinical features

• Aspiration pneumonitis
  • Present hours after aspiration event
  • Range from no symptoms to nonproductive cough, ↓ O2, respiratory distress
  • CXR infiltrates (one or both lower lobes) resolve without antibiotics
• Aspiration pneumonia
  • Present days after aspiration event
  • Fever, cough, ↑ sputum
  • CXR infiltrate in dependent lung segment (classically RLL)
  • Can progress to abscess

Diagnostics

Imaging: The lung region in which the infiltrates are seen depends on the patient’s position on aspiration.

• Supine position: superior segment of the right lower lobe (most common site of aspiration)
• Standing/sitting: posterior basal segment of the right lower lobe
• Right lateral decubitus position: posterior segment of the right upper lobe or right middle lobe