A 70-year-old man presents with fever, productive cough with rusty sputum, and right-sided pleuritic chest pain. Chest X-ray shows consolidation of the entire right lower lobe with air bronchograms. Sputum culture grows lancet-shaped gram-positive diplococci. Which organism is the causative agent?

• A Staphylococcus aureus
• B Klebsiella pneumoniae
• C Haemophilus influenzae
• D Streptococcus pneumoniae ✓

Explanation

Streptococcus pneumoniae is the most common cause of community-acquired lobar pneumonia. It classically presents with rusty sputum, sudden onset fever, and lobar consolidation with air bronchograms. The organism appears as lancet-shaped gram-positive diplococci. Staphylococcus aureus (option A) causes bronchopneumonia, often post-influenza. Klebsiella (option B) causes upper lobe pneumonia with currant-jelly sputum in alcoholics.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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