A decade of antimicrobial resistance in Staphylococcus aureus: A single center experience

Background The emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) resulted in the recommended use of clindamycin and trimethoprim-sulfamethoxazole (TMP-SMX) for suspected S. aureus infections. The objective of this study was to determine the resistance to methicillin, clindamycin, and TMP-SMX in S. aureus isolates during a 10-year period. Methods Retrospective review of the antimicrobial susceptibilities of all S. aureus isolates in the outpatient and inpatient settings at Nationwide Children’s Hospital from 1/1/2005 to 12/31/2014. Duplicate isolates from the same site and year and those obtained for MRSA surveillance or from patients with cystic fibrosis were excluded. Results Of the 57,788 S. aureus isolates from 2005–2014, 40,795 (71%) were included. In the outpatient setting, methicillin resistance decreased from 54% to 44% (p<0.001) while among inpatient isolates, no significant change was observed. From 2009–2014, resistance to clindamycin among outpatient isolates increased from 16% to 17% (p = 0.002) but no significant trend was observed among inpatient isolates (18% to 22%). Similarly, TMP-SMX resistance increased in outpatient S. aureus isolates from 2005–2014 (0.9% to 4%, p<0.001) but not among inpatient isolates. Among both inpatient and outpatient isolates, methicillin-susceptible S. aureus (MSSA) exhibited higher resistance to both clindamycin and TMP-SMX than MRSA. In addition, resistance to methicillin, clindamycin and TMP-SMX varied widely according to the site of specimen collection. Conclusion In a decade where >40,000 S. aureus isolates were identified at a large pediatric hospital, substantial changes in methicillin, clindamycin, and TMP-SMX resistance occurred. These findings highlight the importance of ongoing surveillance of the local antimicrobial resistance in S. aureus in order to guide empiric antimicrobial therapy.