A 62-year-old man with COPD is on mechanical ventilation in the ICU for 10 days. He develops fever, purulent endotracheal secretions, and a new infiltrate on chest X-ray. Sputum culture grows Pseudomonas aeruginosa. What is the most common site of Pseudomonas aeruginosa infection in hospitalized patients?

## Most Common Site of Pseudomonas aeruginosa Infection **Key Point:** Pseudomonas aeruginosa is the most frequent gram-negative pathogen causing ventilator-associated pneumonia (VAP) in ICU patients, accounting for 20–30% of all VAP cases. ### Why the Respiratory Tract? **High-Yield:** P. aeruginosa has a predilection for moist, oxygen-rich environments and biofilm formation on endotracheal tubes. Risk factors include: - Prolonged mechanical ventilation (>48 hours) - Aspiration of contaminated secretions - Impaired mucociliary clearance - Immunosuppression ### Epidemiology in Hospitalized Patients | Site | Frequency | Context | |------|-----------|----------| | Respiratory (VAP) | Most common | Intubated, ICU patients | | Urinary (CAUTI) | Second most common | Foley catheter >7 days | | Bloodstream | Less common | Usually secondary to VAP or CAUTI | | Wound | Least common | Post-operative, burn patients | **Clinical Pearl:** P. aeruginosa in VAP typically presents with purulent, often greenish sputum due to pyoverdine and pyocyanin pigment production. This clinical sign is highly suggestive of Pseudomonas and warrants empiric anti-pseudomonal coverage pending culture confirmation. **Mnemonic — P. aeruginosa Predilections:** **MOIST** = Moist environments, Oxygen-rich sites, Immunocompromised hosts, Synthetic surfaces (catheters), Time-dependent biofilm formation.