An ICU audit categorises cases of ventilator-associated pneumonia by time of onset. A patient intubated for 9 days develops VAP. Compared with early-onset VAP, which organism profile is characteristically responsible for late-onset disease?

• A Streptococcus pneumoniae and Haemophilus influenzae
• B Pseudomonas aeruginosa, Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus ✓
• C Moraxella catarrhalis and anaerobic oral streptococci
• D Legionella pneumophila acquired from contaminated ice machines

Explanation

Late-onset VAP, defined as occurring more than 4 to 5 days after intubation, is caused by multidrug-resistant nosocomial flora such as Pseudomonas, Acinetobacter and MRSA that colonise the oropharynx and lower airway during prolonged ventilation. S. pneumoniae and H. influenzae typify early-onset VAP arising from the patient's own community flora, which is why empiric therapy differs between the two groups. Legionella is an uncommon environmental cause, not a defining late-onset pathogen.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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