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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.

Background: Respiratory syncytial virus (RSV) is the leading cause of severe acute respiratory infections (ARI) in preterm infants. The incidence of RSV-associated hospitalizations has not been defined in Mexico., Objectives: To determine the incidence of ARI- and RSV-associated hospitalizations in preterm infants during the first year of life., Methods: Prospective cohort study of 294 preterm infants followed up through monthly telephone calls and routine outpatient visits. Hospitalized children were identified through daily visits to pediatric wards of participating hospitals and through telephone calls. Respiratory samples were tested for RSV by RT-PCR., Results: Mean gestational age of participating infants was 33 weeks. Ninety-six infants were diagnosed with bronchopulmonary dysplasia (BPD) and 17 with congenital heart disease (CHD); 11 had both conditions. There were 71 hospitalization episodes in 53 infants. Respiratory samples for RSV detection were available in 44 hospitalization episodes, and the result was positive in 16 (36.3%). At least one hospitalization for ARI was recorded in 33 of 96 participants with BPD, in seven of 17 with CHD, and 18 of 192 infants without these diagnoses. Five (71.4%) of CHD infants who required admission also had BPD. RSV-confirmed hospitalization rates were 9.4%, 5.9%, and 2.6% for infants with BPD, CHD, and otherwise healthy preterm infants, respectively. Attributable RSV admission frequencies were estimated to be 13.6%, 16.5%, and 4.1%, respectively., Conclusions: Mexican preterm infants, particularly those with BPD, have high rates of ARI- and RSVassociated hospitalizations. Specific interventions to reduce the incidence of severe infections in this highrisk group are required., (© 2019 The Authors. Influenza and Other Respiratory Viruses Published by John Wiley & Sons Ltd.)