Changes in the Prevalence of Methicillin Resistance Among Healthcare-Associated Staphylococcus aureus Infections, 2009–2018

Abstract

Background:Staphylococcus aureus has long been an important cause of healthcare-associated infections (HAIs) and remains the second most common HAI pathogen in the United States. Often resistant to several antibiotics, S. aureus infections are difficult to treat and can leave patients at risk for serious complications such as pneumonia and sepsis. HAI pathogens and their antimicrobial susceptibility testing (AST) results have been reported to NHSN since its inception in 2005. Previous NHSN surveillance reports have presented national annual benchmarks for antimicrobial resistance phenotypes, such as methicillin-resistant S. aureus (MRSA). Whether there have been any significant changes over time in the prevalence of methicillin resistance among S. aureus infections reported to NHSN has not been previously assessed. Methods:S. aureus AST data from central-line–associated bloodstream infections, catheter-associated urinary tract infections, and inpatient surgical site infections reported from acute-care hospitals between 2009 and 2018 were analyzed. S. aureus was defined as MRSA if it was reported as resistant to oxacillin, cefoxitin, or methicillin. A national percentage resistant (%R) was calculated for each year as the number of resistant pathogens divided by the number of pathogens tested for susceptibility multiplied by 100. A generalized linear mixed model with logistic function was created to evaluate annual changes in the percentage resistant. Several patient-level and hospital-level characteristics were assessed as potential covariates. To account for differential baseline %R values between individual hospitals, specification of random intercept and slope were used during model creation. Differences in the trend of %R between HAI types were assessed using interaction terms. Data were analyzed using SAS v 9.3 software, and P < .05 was considered significant. Results: Overall, 3,317 hospitals reported at least 1 S. aureus pathogen tested for susceptibility between 2009 and 2018. The national unadjusted %R decreased from 49.2% (2009) to 41.2% (2018), with similar decreases seen in each HAI type (Table 1). After adjusting for significant covariates, a statistically significant annual 3% decrease in the prevalence of resistance was observed (Fig. 1). Significant differences between HAI types did not exist. Conclusions: The percentage of healthcare-associated S. aureus resistant to oxacillin, cefoxitin, or methicillin has declined consistently over the past 10 years. Continued efforts in infection prevention and antimicrobial stewardship are vital to sustaining this decline.

Funding: None

Disclosures: None