37. PNEUMONIA

Introduction

Pneumonia is an acute infection of the lung tissue (alveoli and small airways) usually caused by bacteria, viruses or other microbes. The infected areas become filled with fluid or pus (consolidation) which reduces oxygen exchange and causes breathlessness, cough and fever. Pneumonia ranges from mild illness to life-threatening disease, especially in the elderly, infants and people with weak immunity.

Classification

  • Anatomical: Lobar pneumonia (one or more lobes), bronchopneumonia (patchy, lobular) and interstitial pneumonia (mainly interstitium).
  • Etiologic: Bacterial, viral, fungal, mycoplasma, aspiration, anaerobic.
  • Setting-based: Community-acquired pneumonia (CAP), Hospital-acquired pneumonia (HAP) and Ventilator-associated pneumonia (VAP).

Common Causes

  • Bacteria: Streptococcus pneumoniae (most common in CAP), Staphylococcus aureus, Haemophilus influenzae, Klebsiella, Pseudomonas (in HAP).
  • Viruses: Influenza, RSV, SARS-CoV-2, adenovirus.
  • Atypical organisms: Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella.
  • Anaerobes: Often cause aspiration pneumonia (from aspiration of oral/gastric contents).

How Microbes Reach Lungs (Routes)

  • Inhalation of airborne droplets containing organisms.
  • Aspiration of oropharyngeal or gastric contents (common in alcoholics, unconscious patients).
  • Hematogenous spread from distant infections (rare).
  • Direct spread from nearby infected sites (e.g., empyema).

Pathophysiology

When pathogens enter the alveoli, local immune response triggers inflammation. Alveolar macrophages and recruited neutrophils try to clear microbes but also cause fluid and pus accumulation in alveoli (consolidation). This reduces gas exchange, causes V/Q mismatch and hypoxia. In severe disease, systemic inflammatory response may cause sepsis and multi-organ dysfunction.

Predisposing Factors

  • Age (infants, elderly)
  • Smoking, chronic lung disease (COPD, bronchiectasis)
  • Immunosuppression (HIV, steroids, chemotherapy)
  • Recent viral respiratory infection
  • Reduced consciousness, aspiration risk
  • Malnutrition, alcoholism
  • Hospitalization and mechanical ventilation

Clinical Features

  • Fever, chills
  • Cough (may be productive with purulent sputum)
  • Breathlessness, rapid breathing
  • Chest pain – pleuritic (worse on deep breath)
  • Fatigue, poor appetite
  • In elderly: confusion, low-grade fever, decreased appetite
  • On exam: decreased chest expansion, bronchial breath sounds, crackles, dullness on percussion (lobar)

Complications

  • Lung abscess
  • Pleural effusion and empyema
  • Respiratory failure, ARDS
  • Sepsis and multi-organ failure

Diagnosis

  • Chest X-ray: Shows lobar consolidation, patchy infiltrates or interstitial pattern.
  • Sputum Gram stain & culture: Helpful for bacterial diagnosis and antibiotic sensitivity (important in HAP).
  • Blood cultures: Useful if bacteremia is suspected.
  • Pulse oximetry / ABG: Assess oxygenation.
  • Complete blood count: Leukocytosis with neutrophilia in bacterial pneumonia.
  • Urine antigen tests: For Legionella and pneumococcus (rapid support).
  • PCR tests: Useful for viral and atypical pathogens (e.g., influenza, SARS-CoV-2, Mycoplasma).

Treatment (Overview)

Treatment depends on cause, severity, patient age and comorbidities. Start early empiric antibiotics for suspected bacterial pneumonia based on likely pathogens and local guidelines; adjust after culture results.

General measures

  • Oxygen therapy to maintain SpO2 ≥ 92% (or as per comorbidity)
  • Fluids and electrolyte balance
  • Analgesics and antipyretics (paracetamol)
  • Physiotherapy and chest physiotherapy if indicated
  • Hospitalize if severe, elderly, hypoxic or comorbid

Empiric antibiotic examples (follow local/WHO/CDC guidelines)

  • Outpatient (previously healthy): Amoxicillin or amoxicillin–clavulanate ± macrolide (if atypical suspected)
  • Moderate to severe CAP: Beta-lactam + macrolide OR respiratory fluoroquinolone (careful with safety)
  • HAP/VAP: Broad-spectrum therapy covering Pseudomonas, MRSA as per hospital antibiogram; narrow with cultures
  • Aspiration pneumonia: Cover anaerobes — e.g., amoxicillin–clavulanate or clindamycin

Prevention

  • Pneumococcal vaccination for elderly and at-risk groups
  • Annual influenza vaccination
  • Hand hygiene and cough etiquette
  • Smoking cessation
  • Avoid aspiration risk (raise head of bed, careful feeding in neurologically impaired)
  • Hospital infection control to prevent HAP/VAP

When to Seek Medical Help

See a doctor urgently if breathlessness, high fever, chest pain, blood in sputum, confusion or signs of sepsis. Early treatment reduces complications and improves outcomes.

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