In intubated adult ICU patients, the diagnosis of MRSA ventilator-associated pneumonia, or VAP, is based on epidemiologic/microbiologic criteria. The characteristic clinical features of MRSA pneumonia are well-known from decades of clinical experience with MRSA community-acquired pneumonia in patients with influenza. This is the gold standard of diagnosing MRSA pneumonia.

Patients with influenza who have bona fide MRSA pneumonia have several characteristic clinical features, such as otherwise unexplained high spiking fevers, hypotension, cyanosis, leukocytosis and rapidly cavitating infiltrates (< 72 hours) with elastin fibers in airway secretions (diagnostic of necrotizing pneumonia), hemorrhagic tracheobronchitis (due to influenza), and positive sputum culture for MRSA. In patients with influenza, if the methicillin-susceptible Staphylococcus aureus (MSSA) or MRSA strain is positive for Panton-Valentine leukocidin cytotoxin, outcomes are frequently fatal. This clinical presentation differs markedly from the typical intubated ICU patient with low-grade fever, leukocytosis and new infiltrates on chest X-ray with MRSA in respiratory secretion cultures.