Community-Acquired Pneumonia
Infection filling the alveoli with inflammatory exudate outside a hospital setting, so the alveolar space (not the airway) is consolidated, producing focal signs of consolidation, hypoxia and a systemic inflammatory response whose severity must be scored to guide urgent treatment.
First principles
Pneumonia is alveolar filling, not airway narrowing
Pathogens (typically Streptococcus pneumoniae in the community) reach the distal airspaces and trigger an acute inflammatory response: neutrophils, fibrin and oedema fluid flood the alveoli, replacing air with exudate: consolidation. Because it is the alveolar sacs that fill rather than the airways narrowing, the physiology is fundamentally different from asthma or COPD: instead of obstruction to airflow, there is loss of aerated lung tissue available for gas exchange, which is why the affected area sounds and feels solid, not wheezy.
Educational content pending clinical review. Not medical advice.