Rust-colored sputum is classically associated with which pneumonia?

• A. Legionella pneumophila pneumonia
• B. Mycoplasma pneumoniae pneumonia
• C. Klebsiella pneumonia
• D. Pneumococcal pneumonia

Answer: (D)

Rust-colored sputum points to pneumococcal pneumonia, caused by Streptococcus pneumoniae, a classic cause of acute lobar pneumonia. The rust hue comes from blood-tinged sputum as the infection drives intense alveolar inflammation with leakage of red blood cells into the airspaces, mixing with the sputum. This organism is the most common cause of community-acquired pneumonia and is typically associated with a sudden illness, fever, pleuritic chest pain, and productive coughing with the rusty sputum.

Other organisms have distinctive sputum or accompanying features: Legionella often presents with high fever and GI symptoms and can have hyponatremia; Mycoplasma pneumoniae typically causes a milder, walking pneumonia with a nonproductive or scant sputum; Klebsiella can produce thick, currant jelly sputum and is more common in older adults or those with alcohol use and often shows more destructive, necrotizing pneumonia.