Molecular Characteristics and Prevalence of Rifampin Resistance in Staphylococcus aureus Isolates from Patients with Bacteremia in South Korea.

Rifampin resistance (RIF-R) in Staphylococcus aureus (S. aureus) with rpoB mutations as one of its resistance mechanisms has raised concern about clinical treatment and infection prevention strategies. Data on the prevalence and molecular epidemiology of RIF-R S. aureus blood isolates in South Korea are scarce. We used broth microdilution to investigate RIF-R prevalence and analyzed the rpoB gene mutation in 1615 S. aureus blood isolates (772 methicillin-susceptible and 843 methicillin-resistant S. aureus (MRSA)) from patients with bacteremia, between 2008 and 2017. RIF-R prevalence and antimicrobial susceptibility were determined. Multilocus sequence typing was used to characterize the isolate's molecular epidemiology; Staphylococcus protein A (spa), staphylococcal cassette chromosome mec (SCCmec), and rpoB gene mutations were detected by PCR. Among 52 RIF-R MRSA isolates out of 57 RIF-R S. aureus blood isolates (57/1615, 0.4%; 5 methicillin-susceptible and 52 MRSA), ST5 (44/52, 84.6%), SCCmec IIb (40/52, 76.9%), and spa t2460 (27/52, 51.9%) were predominant. rpoB gene mutations with amino acid substitutions showed that A477D (17/48, 35.4%) frequently conferred high-level RIF resistance (MIC > 128 mg/L), followed by H481Y (4/48, 8.3%). RIF-R S. aureus blood isolates in South Korea have unique molecular characteristics and are closely associated with rpoB gene mutations. RIF-R surveillance through S. aureus-blood isolate epidemiology could enable effective therapeutic management.

Impact of neutropenia on the clinical outcomes of Staphylococcus aureus bacteremia in patients with hematologic malignancies: a 10-year experience in a tertiary care hospital.

Staphylococcus aureus bacteremia is one of the most serious bacterial infections and may lead to worse clinical outcomes in patients with prolonged severe neutropenia. However, clinical data on S. aureus bacteremia in neutropenic patients with hematologic malignancies are limited. We conducted two case-control studies using a 10-year prospective cohort of patients with S. aureus bacteremia. Neutropenic and non-neutropenic hematologic malignancy patients were compared on clinical characteristics and treatment outcomes. An additional matched case-control study using solid tumor patients was conducted. Risk factors for 12-week mortality were analyzed. Of 1643 patients with S. aureus bacteremia, 64 (3.9%) neutropenic and 108 (6.6%) non-neutropenic patients with hematologic malignancies were included in the study. There were no significant differences in the incidence of metastatic infection between the two groups (17.2% vs. 17.6%, p = 0.95), in contrast with a previous study that observed no metastatic infection in neutropenic patients. Twelve-week mortality in neutropenic patients with hematologic malignancies tended to be lower than in non-neutropenic patients with hematologic malignancies (15.6% vs. 26.9%, p = 0.09) and was significantly lower than in neutropenic patients with solid tumors (15.6% vs. 45.8%, p = 0.003). Independent risk factors for mortality in hematologic malignancy patients with S. aureus bacteremia were high Charlson comorbidity score, high APACHE II score, and skin and soft tissue infection. Neutropenia was not independently associated with mortality. Our findings suggest that neutropenia in hematologic malignancies may not affect the incidence of metastatic infection or 12-week mortality of S. aureus bacteremia.

Long-term methicillin-resistant Staphylococcus aureus bacteremia persisting for more than 2 weeks: risk factors and outcomes.

The clinical significance of long-term methicillin-resistant Staphylococcus aureus (MRSA) bacteremia remains unclear. We evaluated the clinical, microbiological characteristics, and clinical outcomes of long-term MRSA bacteremia. A nested case-control study was conducted in a prospective cohort of adult patients with MRSA bacteremia at a tertiary hospital between August 2008 and December 2017. Patients with long-term MRSA bacteremia (≥ 14 days) were compared with control patients, defined as having bacteremia that resolved in less than 3 days. The following variables were documented: heteroresistance phenotype, genotypes, agr dysfunction, and the presence of 41 virulence genes in isolates. Of the total 890 patients studied, 69 patients (7.8%) exhibited long-term MRSA bacteremia and 599 (67.3%) exhibited resolving bacteremia. The most common sources of long-term bacteremia were central venous catheter-related infection (39%) and osteomyelitis (19%). Independent risk factors for long-term MRSA bacteremia included male sex (adjusted odds ratio [aOR] = 2.43), community-acquired bacteremia (aOR = 2.93), the presence of a prosthetic device (aOR = 3.40), and osteomyelitis (aOR = 7.98). Metastatic infections developed more frequently in patients with long-term bacteremia than in those with resolving bacteremia (56.5% vs. 8.0%; P < 0.001). Although there were no significant differences in 30-day, 12-week, or in-hospital mortality rates between the two groups, infection-attributable mortality was higher in the long-term bacteremia group (23.2% vs. 11.5%; P = 0.01). Microbiological characteristics did not differ significantly between the two groups. Clinical factors, including community-acquired bacteremia, the presence of a prosthetic device, and osteomyelitis, appear to contribute to long-term MRSA bacteremia more than microbiological factors.