ICU · Infectious Diseases

Acute severe community-acquired pneumonia: MRSA pneumonia

Also known as MRSA pneumonia · Community-acquired MRSA pneumonia · PVL-positive S. aureus · Necrotising pneumonia · Healthcare-associated MRSA pneumonia · Staphylococcal necrotising pneumonia

MRSA pneumonia in ICU: two epidemiologically and mechanistically distinct syndromes — healthcare-associated (HA-MRSA, nosocomial, multidrug resistant, SCCmec types I–III, lacks PVL) and community-acquired (CA-MRSA, often PVL-positive, SCCmec types IV–V, highly virulent, necrotising). Resistance is mediated by the mecA/mecC gene encoding PBP2a (penicillin-binding protein 2a) — an altered transpeptidase with low affinity for all beta-lactam antibiotics, rendering the entire beta-lactam class (including carbapenems) ineffective. Risk factors: post-influenza viral pneumonia (1 risk for CA-MRSA), recent hospitalisation (<90 days), IV antibiotics (<90 days), nursing home residence, haemodialysis, central venous catheter, IVDU, known MRSA colonisation, skin/soft tissue infection (CA-MRSA), age >65, immunocompromise. Presentation: severe CAP with rapid progression, multilobar infiltrates, cavitation (necrotising — hallmark of PVL-positive strains), haemoptysis, bacteraemia, septic shock, leucopenia. Diagnosis: nasal swab PCR screening (high negative predictive value), sputum/blood culture, PVL gene detection (PCR for lukS-PV/lukF-PV), echocardiography for all bacteraemia. Treatment: vancomycin (15 mg/kg IV every 12 hours, trough-adjusted, AUC/MIC target 400-600) OR linezolid 600 mg every 12 hours (PREFERRED for pneumonia — epithelial lining fluid penetration approximating 100% of plasma, suppresses PVL/alpha-haemolysin production, less nephrotoxicity) with clindamycin as an anti-toxin adjunct if susceptible. Duration: 7-14 days (longer if bacteraemia, endocarditis, metastatic infection). Always search for metastatic infection (vertebral osteomyelitis, psoas/epidural abscess, endocarditis). Mortality: 60-day mortality 15.7-17.0% in the pivotal MRSA nosocomial pneumonia RCT; PVL-positive necrotising disease the fulminant end (48-hour survival 63%).