Rust-colored sputum in lobar pneumonia is most characteristic of which etiologic agent?

• A. Streptococcus pyogenes
• B. Streptococcus pneumoniae
• C. Corynebacterium jeikeium
• D. Staphylococcus aureus

Answer: (B)

Rust-colored sputum with a sudden, single-lobe consolidation is the classic clue for pneumococcal pneumonia. The organism responsible, Streptococcus pneumoniae, is a Gram-positive, lancet-shaped diplococcus that classically causes abrupt lobar pneumonia with a productive cough. The rust color comes from blood-tinged exudate as neutrophils flood the alveoli and the infection fills the airspaces, a hallmark presentation taught for this pathogen.

Other organisms listed don’t fit this classic pattern as neatly. Streptococcus pyogenes often causes throat infections or skin infections and only occasionally pneumonia. Corynebacterium jeikeium is more of a nosocomial opportunist in immunocompromised patients. Staphylococcus aureus pneumonia can occur—especially after influenza—but it more commonly presents with patchy, multifocal infiltrates and can lead to abscesses rather than the typical rust-colored sputum of classic pneumococcal lobar pneumonia.