Rapid De-escalation of Anti-MRSA Therapy Guided by S. Aureus Nares Screening in Case of Pneumonia (SNAP Study)

BACKGROUND On the basis of current IDSA/ATS guidelines antimicrobial agents such as Linezolid and Vancomycin are commonly used in hospitalized patients as an empirical treatment in community acquired pneumonias (CAPs) particularly in hospital-acquired pneumonias (HAPs) and ventilator associated pneumonias (VAPs), suggesting the empiric use of such anti-MRSA agents for patients with specific risk factors (e.g. recent hospitalization, exposure to parenteral antibiotics and/or previous isolation of these organisms, in particular from the respiratory tract) while obtaining culture data.

According to the 2023 annual report of the European Antibiotic Resistance Surveillance System (EARSS) there is a high prevalence of MRSA throughout the European territory, however, even in countries with high endemicity, the presence of MRSA has remained stable in the last years. In Italy, according to the National Antibiotic-Resistance Surveillance System AR-ISS, in 2021 the percentage of blood isolates MRSA isolates showed a reduction (29.9%) in the national territory, standing, however, at 33.6% in the Puglia region, a percentage higher than the European.

In patients with pneumonia, the nasal PCR-assay for MRSA has a high negative predictive value (NPV), with the crucial implication that a negative result can be used to guide the antibiotic de-escalation, avoiding an improper empiric use of the anti-MRSA therapy. Data supporting the clinical validity of the use of the nasal swab for MRSA as a diagnostic tool for pneumonia are robust, in this regard, as stated by the IDSA/ATS guidelines and supported by numerous retrospective studies, anti-MRSA treatment can be avoided in case of negative result, especially in non-severe CAP, thus preventing the misuse of anti-MRSA drugs.

The indiscriminate use of these drugs over time has considerably led to the selection of resistant strains of S. aureus such as Vancomycin-intermediate Staphylococcus aureus (VISA), heterogeneous VISA (hVISA) and Vancomycin-resistant Staphylococcus aureus (VRSA). Furthermore, the high risk of adverse events given by the empirical use of anti-MRSA drugs should also be noted including, among others, nephrotoxicity and ototoxicity with vancomycin and bone marrow suppression and peripheral neuropathy with linezolid, without a gain in terms of survival and with longer hospitalization stays.

In addition, the systematic use of such drugs is associated with an increase in hospital costs, where the PCR assay for MRSA has a relevant role. According to a study conducted by the Stanford University in 2021, enabling antibiotic de-escalation within 24h, its use has of facts led to a cost saving of vancomycin of $40.33 per patient.