Does MRSA (Methicillin-resistant Staphylococcus aureus) colonization in the nares predict hospital-acquired pneumonia and secondary bacterial pneumonia?

From the Guidelines

MRSA colonization in the nares is a significant predictor of hospital-acquired pneumonia and secondary bacterial pneumonia, particularly in high-risk settings such as intensive care units. The relationship between MRSA nares colonization and the development of hospital-acquired pneumonia and secondary bacterial pneumonia is well-established, with colonized patients being approximately 2-4 times more likely to develop MRSA pneumonia compared to non-colonized patients 1.

Key Points to Consider

• The predictive relationship exists because the nares serve as a reservoir for MRSA, which can be aspirated into the lungs or spread via healthcare workers' hands.
• Risk factors that increase the likelihood of colonized patients developing pneumonia include mechanical ventilation, recent antibiotic use, advanced age, immunosuppression, and underlying lung disease.
• Screening for nasal MRSA is most valuable in high-risk settings such as intensive care units or before certain surgeries.
• When MRSA pneumonia is suspected, empiric treatment typically includes vancomycin (15-20 mg/kg IV every 8-12 hours, adjusted for renal function) or linezolid (600 mg IV/oral twice daily) while awaiting culture results 1.
• Regular hand hygiene, contact precautions for colonized patients, and decolonization protocols in high-risk settings can help reduce transmission.

Management of Hospital-Acquired Pneumonia

According to the 2017 international guidelines for the management of hospital-acquired pneumonia and ventilator-associated pneumonia, initial empiric therapy should be determined by the patient's risk for MDR pathogens and mortality 1.

• For high-risk patients, initial empiric therapy should include a dual-pseudomonal regimen plus MRSA coverage, if the ICU has >25% of S. aureus respiratory isolates as MRSA.
• The dual-pseudomonal regimen should include an antipseudomonal β-lactam plus a second agent such as an aminoglycoside or an antipseudomonal quinolone.

Treatment Options

Treatment options for MRSA pneumonia include vancomycin and linezolid, with the choice of agent depending on the patient's renal function, severity of illness, and local antimicrobial resistance patterns 1.

• Vancomycin should be dosed at 15-20 mg/kg IV every 8-12 hours, adjusted for renal function.
• Linezolid should be dosed at 600 mg IV/oral twice daily.

From the Research

MRSA Nares Screening and Hospital-Acquired Pneumonia

• MRSA (Methicillin-resistant Staphylococcus aureus) colonization in the nares has been studied as a potential predictor of hospital-acquired pneumonia and secondary bacterial pneumonia 2.
• The diagnostic value of MRSA nasal screening in MRSA pneumonia has been evaluated in a meta-analysis, which found that MRSA nares screening had a high specificity and negative predictive value (NPV) for ruling out MRSA pneumonia, particularly in cases of community-acquired pneumonia (CAP) and healthcare-associated pneumonia (HCAP) 2.

Predictive Value of MRSA Nares Screening

• The pooled sensitivity and specificity of MRSA nares screen for all MRSA pneumonia types were 70.9% and 90.3%, respectively 2.
• With a 10% prevalence of potential MRSA pneumonia, the calculated positive predictive value (PPV) was 44.8%, and the NPV was 96.5% 2.
• For CAP and HCAP, the PPV and NPV increased to 56.8% and 98.1%, respectively 2.

Clinical Implications

• MRSA nares screening can be a valuable tool for antimicrobial stewardship (AMS) to streamline empiric antibiotic therapy, especially among patients with pneumonia who are not colonized with MRSA 2.
• The high NPV of MRSA nares screening suggests that it can be used to rule out MRSA pneumonia, reducing the need for unnecessary empiric MRSA therapy 2.
• However, the predictive value of MRSA nares screening may vary depending on the type of pneumonia, with lower sensitivity and specificity for ventilator-associated pneumonia 2.