There is limited understanding of the geographic diversity and temporal trends in the prevalence of S aureus resistance to non–β-lactams in the United States. In this JAMA study of outpatient S aureus isolates, methicillin-resistant S aureus (MRSA) prevalence declined over a decade, accompanied by rising resistance to tetracyclines and trimethoprim-sulfamethoxazole (TMP-SMX) among MRSA strains.
Nationwide, the proportion of MRSA decreased from 53.6% in 2010 to 38.8% in 2019. The study analyzed 382,149 S aureus isolates from 268,214 unique outpatients with an average age of 63.4, and 94.29% male. Among MRSA isolates, there was a significant increase in resistance to tetracycline (from 3.6% to 12.8% in 2019, and TMP-SMX (from 2.6% to 9.2% in 2019, with modest increases in clindamycin resistance from 24.2% to 30.6% in 2019, and a significant decrease in macrolide resistance from 73.5% to 60.2% in 2019. Among methicillin-sensitive S aureus (MSSA) isolates, significant upward trends were observed in clindamycin, tetracycline, and TMP-SMX resistance. For instance, tetracycline resistance rose from 3.7% in 2010 to 9.1% in 2019.
Geospatial analysis revealed no overlap in counties with high resistance rates to tetracyclines and TMP-SMX. Examining regional variations in antibiotic resistance can guide empirical therapy recommendations and enhance understanding of S aureus resistance evolution.
3 Key Takeaways
- The study observed a significant decline in MRSA prevalence among outpatient infections in the United States from 53.6% in 2010 to 38.8% in 2019.
- Resistance to tetracyclines and TMP-SMX increased notably among both MRSA and MSSA isolates during the study period, highlighting a concerning trend in antibiotic resistance evolution.
- Geographic analysis revealed distinct regional variations in antibiotic resistance profiles for S. aureus, suggesting the importance of localized surveillance to guide effective empirical treatment strategies across different regions of the US.
“Rates of MRSA were highest in the South over the duration of the study period. Prior work has suggested that the combination of sociodemographic factors (eg, crowding, poverty), climate factors (eg, heat, humidity), and antibiotic prescribing patterns have contributed to consistently higher rates of antimicrobial resistance in the South. Climate factors and changing behavior in patient population also likely play a role in the seasonality of S aureus infections observed in the patient cohort,” according to the investigators.1
This cross-sectional study utilized data from Veterans Health Administration (VHA) clinics, encompassing adult outpatients diagnosed with S aureus infection across the contiguous 48 states and Washington, DC, from January 1, 2010, to December 31, 2019. Data analysis was conducted between January and November 2023. The study assessed spatiotemporal variations in S aureus resistance to 4 classes of non-β-lactam antibiotics, stratified by MRSA and MSSA, across different regions of the US. Trend analyses and bivariate mapping were employed to identify significant changes in resistance rates over time and pinpoint counties with high resistance to multiple non-β-lactam antibiotics.
The study used data primarily from the VHA, which has older male patients and may not fully represent the broader US population, though it offers better geographic representation than other surveillance groups. It focused on outpatient S aureus infections, excluding analysis of rural-urban differences and inpatient cases. The study concluded before the COVID-19 pandemic to avoid its confounding effects, suggesting further research to assess post-pandemic antimicrobial resistance trends.
“S aureus is a significant pathogen commonly implicated in serious infections including endocarditis, osteomyelitis, and pneumonia. In the setting of bloodstream infections, 30-day infection-related mortality and 30-day mortality rates approximate 13% and 20%, respectively.1,2 These rates may be even higher in patients with persistent MSSA bacteremia, defined as positive blood cultures for a period of 2 to 7 days despite appropriate antibiotics.”2
While national MRSA prevalence has decreased, the study underscores the importance of regional antibiotic resistance surveillance. Clinicians are urged to stay informed about local resistance profiles to optimize treatment decisions and combat antimicrobial resistance effectively.
References
Carrel M, Smith M, Shi Q, et al. Antimicrobial Resistance Patterns of Outpatient Staphylococcus aureus Isolates. JAMA Netw Open. 2024;7(6):e2417199. doi:10.1001/jamanetworkopen.2024.17199
