- Streptococcus pneumoniae is the leading cause of community-acquired pneumonia in adults due to its high prevalence in the upper respiratory tract and ability to evade host defenses.
- It typically presents with sudden onset of fever, productive cough with purulent sputum, and chest pain.
- The organism’s polysaccharide capsule is a key virulence factor that enables it to resist phagocytosis and establish infection.
- Pneumococcal pneumonia is associated with lobar consolidation visible on chest X-ray, distinguishing it clinically and radiologically from atypical pneumonias.
- Effective treatment relies on antibiotics targeting this bacterium, emphasizing its importance as the primary causative agent in adult community-acquired pneumonia.

Reference: Davidson’s Principles and Practice of Medicine, 24th Edition, Chapter: Lower Respiratory Tract Infections, Page 697.