- Fluid infected, most often a complication of pneumonia
- Common bacterial organisms: h flu, strep, staph, other
- Infection can be introduced also via trauma, procedures, hematogenous spread
- Anaerobes/gnrs less common--> assoc w/aspiration
- Mycobacteria associated w/acute or chronic TB; often frail/compromised
- Fungal→ immunocompromised/chronic
- Decreased breath sounds over effusion, dullness
- Other findings based on magnitude of illness, co-existent pneumonia