The increasing use of chlorhexidine for methicillin-resistant Staphylococcus aureus (MRSA) decolonization has raised concerns about the emergence of resistance to these agents. However, the clinical significance of MRSA positive for the qacA and qacB chlorhexidine tolerance genes has not been established. We investigated the clinical features and predictive factors of MRSA bloodstream infection (BSI) isolates, caused by qacA-and qacB-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 qacA/B. The annual frequency of qacA-and qacB-positive MRSA bacteremia did not change significantly over the study period. Patients infected with qacA-and qacB-positive MRSA had common risk factors for health care-associated infections, including prior antibiotic use, central venous catheterization in situ, intensive care unit-acquired bacteremia, and nosocomial infection. The qacA-and qacBpositive isolates were also associated with an increasing chlorhexidine MIC and resistance to non-␤-lactam antibiotics. The qacA-and qacB-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, qacA-and qacB-positive MRSA isolates were found to be associated with agr 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 qacA and qacB carriage provide a selective advantage for specific MRSA strains in hospital environments.

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Background and Objectives: Nontuberculous mycobacteria (NTM) infections are increasing worldwide. We evaluated the annual trends of NTM isolation on acid-fast bacillus (AFB) culture, compared to that of Mycobacterium tuberculosis, and the distribution of NTM species nationwide in South Korea. Materials and Methods: The study was conducted in a diagnostic center that is a major referral laboratory for the diagnosis of tuberculosis and NTM in South Korea. All laboratory results of AFB culture from January 2014 to December 2019 were collected. All NTM identified were definitively identified to the species level. Results: A total of 345,871 tests were performed for the diagnosis of mycobacteria. The isolation rate of NTM and M. tuberculosis was 3.7% (12,969 cases) and 4.4% (15,081 cases), respectively. The annual isolation rate of NTM increased gradually from 2.7% in 2014 to 4.8% in 2019, whereas that of M. tuberculosis decreased from 6.2% to 3.3%. There were 4988 cases of NTM identified to the species level. M. avium complex (MAC) was the most common species isolated from pulmonary sites (59.8%), followed by M. gordonae (9.2%), M. abscessus (7.0%), and M. fortuitum (5.5%). Extrapulmonary NTM were identified in 29 cases (0.6%). MAC was also the most common NTM species isolated from extrapulmonary sites (65.5%), followed by M. kansasii (10.3%), M. abscessus (6.9%), and M. fortuitum (6.9%). Conclusions: The annual isolation rate of NTM has increased gradually, whereas that of M. tuberculosis has decreased. Follow-up studies of the increases in NTM identification and NTM infections in South Korea are needed.

Granulomatosis with polyangiitis (GPA) is an autoimmune disease which is a type of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis that frequently affects the lungs and kidneys. However, GPA limited to a single organ has also been reported. A 71-year-old man was admitted for back pain and fever. We detected elevated levels of inflammatory markers and myeloperoxidase-ANCA. Magnetic resonance imaging indicated diffuse inflammation of the back and psoas muscles. Histology showed degenerated muscle fibers and granulomatosis vasculitis with mixed lymphoplasma cell infiltration. High-dose methylprednisolone therapy improved his symptoms. A final diagnosis of GPA limited to the muscles was made.