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Pneumonia: Pathophysiology, Causes, and Clinical Presentation

Pneumonia is an infection of the alveolar spaces (air sacs) causing inflammation and exudation. It is a leading cause of infectious mortality worldwide.

Pathophysiology

Pathogen reaches alveoli (aspiration, inhalation, hematogenous).
Alveolar macrophages release cytokines (TNF‑α, IL‑1, IL‑6) → neutrophil recruitment.
Exudate (fibrin, neutrophils, erythrocytes, organisms) fills alveoli → consolidation.
Impaired gas exchange (V/Q mismatch, shunt) → hypoxemia.

Major Etiologic Categories

Category	Key Pathogens	Clinical Clues
Typical bacterial	S. pneumoniae, H. influenzae, M. catarrhalis	Abrupt onset, high fever, rusty sputum, lobar consolidation
Atypical bacterial	M. pneumoniae, C. pneumoniae, Legionella	Subacute, dry cough, headache, patchy infiltrates
Viral	Influenza, RSV, SARS‑CoV‑2, adenovirus	Seasonal, systemic symptoms, bilateral ground‑glass
Fungal	Histoplasma, Coccidioides, Pneumocystis	Endemic exposure, immunocompromised, chronic

Clinical Presentation

Fever, chills, rigors
Cough (productive vs. dry)
Dyspnea, pleuritic chest pain
Tachycardia, tachypnea, hypoxia
Confusion (especially elderly)

Severity Assessment

CURB‑65 or PSI score guides outpatient vs. inpatient vs. ICU management.

Early appropriate antibiotics (guided by local epidemiology and severity) reduce mortality. Vaccination (pneumococcal, influenza, COVID‑19) prevents a substantial fraction of cases.

Infektionskrankheiten

Gesundheitswissenschaften