What distinguishes community-acquired pneumonia (CAP) from hospital-acquired pneumonia (HAP) in onset and common pathogens?

• A. CAP occurs outside healthcare facilities; typical pathogens include Streptococcus pneumoniae; HAP occurs after 48 hours in hospital and often involves MRSA, Pseudomonas.
• B. CAP occurs after 48 hours in hospital; HAP occurs outside healthcare facilities; typical pathogens include Streptococcus pneumoniae.
• C. CAP is viral; HAP is bacterial.
• D. CAP includes MRSA; HAP does not.

Answer: (A)

The distinction hinges on where the infection starts and the organisms expected in that setting. Community-acquired pneumonia begins outside the hospital and is most commonly caused by Streptococcus pneumoniae, a typical community pathogen. Hospital-acquired pneumonia is defined by onset after about 48 hours of hospitalization and is linked to organisms common in the hospital environment that are often more resistant, especially MRSA and Pseudomonas aeruginosa, among others. This timing and the associated pathogens guide empiric therapy: CAP targets community bacteria, while HAP treatment covers resistant hospital flora. The idea that CAP starts after 48 hours in the hospital or that CAP is defined by viral etiology isn’t correct, and HAP routinely includes organisms like MRSA and Pseudomonas rather than excluding them.