Pneumonia: Etiology, Pathogenesis, Stages, Morphology, and Complications

Introduction

Pneumonia is a serious respiratory infection affecting the lungs' air sacs, leading to inflammation and fluid accumulation. Understanding its causes, progression, and complications is essential for effective treatment and prevention.

Etiology of Pneumonia

Causes

• Bacterial: Streptococcus pneumoniae, Haemophilus influenzae
• Viral: Influenza virus, SARS-CoV-2
• Fungal: Histoplasma capsulatum, Pneumocystis jirovecii

Risk Factors

• Age (young children and elderly)
• Smoking and chronic lung diseases
• Immunocompromised conditions
• Hospitalization and mechanical ventilation

Classification

• Community-acquired pneumonia (CAP)
• Hospital-acquired pneumonia (HAP)
• Ventilator-associated pneumonia (VAP)
• Aspiration pneumonia

Pathogenesis

Pneumonia develops when pathogens invade lung tissue, triggering an immune response. Inflammation leads to alveolar filling with fluid and inflammatory cells, compromising gas exchange.

Stages of Pneumonia

1. Congestion: Initial infection with vascular engorgement and edema.
2. Red Hepatization: Alveoli fill with inflammatory cells, resembling liver tissue.
3. Gray Hepatization: Breakdown of red blood cells and fibrin deposition.
4. Resolution: Gradual clearing of inflammatory exudates.

Morphology and Complications

Pneumonia can lead to lung consolidation, abscess formation, and pleural effusions. If untreated, severe cases may result in respiratory failure or sepsis.

Conclusion

Recognizing pneumonia’s etiology, pathogenesis, and complications is critical for effective management. Early diagnosis and appropriate treatment significantly reduce morbidity and mortality.