Clinical and Molecular Characteristics of qacA - and qacB -Positive Methicillin-Resistant Staphylococcus aureus Causing Bloodstream Infections

The increasing use of chlorhexidine for methicillin-resistant (MRSA) decolonization has raised concerns about the emergence of resistance to these agents. However, the clinical significance of MRSA positive for the and chlorhexidine tolerance genes has not been established. We investigated the clinical features and predictive factors of MRSA bloodstream infection (BSI) isolates, caused by - and -positive MRSA, from 2010 to 2016 at a tertiary hospital in South Korea. A total of 246 MRSA BSI isolates were included; 71 (28.9%) isolates carried The annual frequency of - and -positive MRSA bacteremia did not change significantly over the study period. Patients infected with - and -positive MRSA had common risk factors for health care-associated infections, including prior antibiotic use, central venous catheterization , intensive care unit-acquired bacteremia, and nosocomial infection. The - and -positive isolates were also associated with an increasing chlorhexidine MIC and resistance to non-β-lactam antibiotics. The - and -positive isolates were more likely to belong to sequence type 5 (ST5), which is a common health care-associated MRSA strain in South Korea. In multivariable analyses, - and -positive MRSA isolates were found to be associated with dysfunction (adjusted odds ratio [aOR], 6.45; 95% confidence interval [CI], 2.59 to 16.10), ST5 MRSA strain (aOR, 4.96; 95% CI, 1.85 to 13.26), nosocomial infection (aOR, 4.88; 95% CI, 2.20 to 10.83), and antibiotic use within the previous 3 months (aOR, 2.59; 95% CI, 1.20 to 5.59). These findings suggest that the microbiological features of and carriage provide a selective advantage for specific MRSA strains in hospital environments.