TEN-YEAR FOLLOW-UP OF MSSA TREATMENT PRESCRIPTION BEHAVIOR AND POST-PRESCRIPTION AMS INTERVENTION IMPACT

Intro: Methicillin susceptibility prevails within clinically relevant Staphylococcus aureus strains. This study aimed to describe proportions of Methicillin- Susceptible S. aureus (MSSA), prescription behavior for its treatment, and impact of a post-prescription antimicrobial stewardship (AMS) strategy within two private tertiary care Mexican hospitals over 10 years. Methods: Patients older than 14 years with an S. aureus culture-proven infection between 2011 to 2020 were included. Disease was classified as monomicrobial or polymicrobial; strains were classified as MSSA if Cefoxitin susceptible. Spectrum Score was calculated according to the participants’ antibiotic regimen at: admission, 72 hours after culture results, and end-of- therapy. During the last two years analyzed, post-prescription review with feedback to prescribers as an AMS strategy. MSSA rates were compared within both time periods. Findings: We identified 1322 clinically relevant S. aureus strains isolated from 2011 to 2020. A total of 817 specimens were MSSA (61.8%), while only 505 demonstrated methicillin resistance(38.2%). During the antimicrobial stewardship period, MSSA proportion increased by 21.6% compared to the pre- intervention period(78.9% vs 57.3%). In patients with monomicrobial MSSA infections, mean decrease Spectrum Score was lower at end of therapy in comparison to that calculated 72 hours after culture results(1.3 vs 0.2 points). The latter didn't seem to differ when contrasting the Spectrum score between the period before(0.3 points) and after(0.2 points) the AMS intervention. The three most commonly used antimicrobials at admission, 72 hours after culture results, and end of therapy were respectively: Ceftriaxone, Meropenem, Vancomycin; Clindamycin, Vancomycin, Linezolid; and Trimethoprim/Sulfamethoxazole, Clindamycin, Ciprofloxacin. Conclusion: MSSA caused more infections in comparison to methicillin-resistant strains in our studied population. Despite the poor antimicrobial de-escalation in MSSA infections, evidenced by the high Spectrum scores, methicillin resistance has decreased over time. Post prescription interventions have not proven to be effective at these private hospitals and AMS strategies should be expanded to continue avoiding antibiotic resistance.