A Longitudinal Study of Adult Patients with Staphylococcus aureus Bacteremia over 11 Years in Korea.

BACKGROUND: The temporal changes in the Staphylococcus aureus genotypes causing S. aureus bacteremia (SAB) and the corresponding clinical changes over the last decade in South Korea are rarely investigated. METHODS: A longitudinal study of adult SAB patients was conducted in a large referral hospital in Seoul, South Korea. Adult monomicrobial SAB patients were enrolled between August 2008 and December 2018. Genotyping was performed by multilocus sequence typing (MLST) and staphylococcal protein A (spa) typing. Trends in changes were identified by linear regression analysis. RESULTS: Of 1782 adult SAB patients, the blood isolates of 1,778 (99.8%) and 1,634 (91.7%) were determined to be MLST and spa type, respectively. ST5 (-2.626%/year) and ST239 (-0.354%/year) decreased during the study period (P < 0.001 for both), but ST72 (2.009%/yr)-and ST8 (0.567%/yr) increased (P < 0.001 for both). The most common genotype was changed from ST5 in 2008 (44.9%) to ST72 in 2018 (36.3%). Panton-Valentine leukocidin-positive spa-t008-MRSA (USA300) was found in 28.6%. Central venous catheter (CVC)-related SAB (-2.440%/yr) and persistent SAB (-1.016%/yr) decreased, but mortality and recurrence rates were unchanged. CONCLUSION: Over the last decade, the hospital clones ST5 and ST239 have been replaced by community genotype ST72. This was associated with decreased CVC-related and persistent SAB. Increased USA300 was observed in community and hospital settings. Further research is required to identify the reasons for the ST72 epidemic and predict the impending epidemic of ST8 strains, including USA300.

Selection of an appropriate empiric antibiotic regimen in hematogenous vertebral osteomyelitis.

BACKGROUND: Empiric antibiotic therapy for suspected hematogenous vertebral osteomyelitis (HVO) should be initiated immediately in seriously ill patients and may be required in those with negative microbiological results. The aim of this study was to inform the appropriate selection of empiric antibiotic regimens for the treatment of suspected HVO by analyzing antimicrobial susceptibility of isolated bacteria from microbiologically proven HVO. METHOD: We conducted a retrospective chart review of adult patients with microbiologically proven HVO in five tertiary-care hospitals over a 7-year period. The appropriateness of empiric antibiotic regimens was assessed based on the antibiotic susceptibility profiles of isolated bacteria. RESULTS: In total, 358 cases of microbiologically proven HVO were identified. The main causative pathogens identified were methicillin-susceptible Staphylococcus aureus (33.5%), followed by methicillin-resistant S. aureus (MRSA) (24.9%), Enterobacteriaceae (19.3%), and Streptococcus species (11.7%). Extended spectrum ß-lactamase (ESBL)-producing Enterobacteriaceae and anaerobes accounted for only 1.7% and 1.4%, respectively, of the causative pathogens. Overall, 73.5% of isolated pathogens were susceptible to levofloxacin plus rifampicin, 71.2% to levofloxacin plus clindamycin, and 64.5% to amoxicillin-clavulanate plus ciprofloxacin. The susceptibility to these oral combinations was lower in cases of healthcare-associated HVO (52.6%, 49.6%, and 37.6%, respectively) than in cases of community-acquired HVO (85.8%, 84.0%, and 80.4%, respectively). Vancomycin combined with ciprofloxacin, ceftriaxone, ceftazidime, or cefepime was similarly appropriate (susceptibility rates of 93.0%, 94.1%, 95.8%, and 95.8%, respectively). CONCLUSIONS: Based on our susceptibility data, vancomycin combined with a broad-spectrum cephalosporin or fluoroquinolone may be appropriate for empiric treatment of HVO. Fluoroquinolone-based oral combinations may be not appropriate due to frequent resistance to these agents, especially in cases of healthcare-associated HVO.

Impact of immune status on the clinical characteristics and treatment outcomes of nocardiosis.

Nocardiosis occurs in both immunocompromised and immunocompetent patients. We aimed to assess how its characteristics differ depending on patients' immune status. Of a total of 54 patients with culture-proven nocardiosis diagnosed over 13 years, 18 (33%) were immunocompetent. Half of immunocompetent patients had chronic lung disease and were not receiving systemic corticosteroid. There were no significant differences in clinical, radiographic, and microbiologic characteristics, and treatment outcomes according to immune status, except that pulmonary cavitation (47% vs. 8%) and coexisting infections (17% vs. 0%) were more frequent in immunocompromised hosts. Nocardia farcinica, the most commonly identified isolates at the species level (51%), was highly susceptible to trimethoprim-sulfamethoxazole (100%) and highly resistant to ceftriaxone (94%). Nocardiosis should be considered in differential diagnosis of pneumonia, brain abscess, or soft tissue infection that does not respond to conventional antibiotic therapy such as ceftriaxone, regardless of whether the patient is immunocompromised or not.

Ciprofloxacin usage and bacterial resistance patterns in Crohn's disease patients with abscesses.

BACKGROUND: Ciprofloxacin is the antibiotic most frequently used in the treatment of Crohn's disease (CD). We attempted to identify the microorganisms present in CD-related intra-abdominal abscesses, their ciprofloxacin resistance patterns, and the clinical impact. METHODS: Microorganisms, their ciprofloxacin resistance, and clinical outcomes were retrospectively analyzed in 78 CD patients with intra-abdominal abscesses, who underwent percutaneous drainage between March 1991, and November 2011. RESULTS: The median time from diagnosis of CD to abscess drainage was 59.5 months (range, 1 to 178 mo). As for bacteriology, the no-growth proportion was 38.5% (n=30), and 69 microorganisms belonging to 11 genera were isolated from the other 48 (61.5%) patients. Of the 69 microorganisms, 65 were bacteria, including 30 (43.4%) gram-positive, 28 (40.6%) gram-negative aerobes, 7 (10.1%) gram-negative anaerobes, and 4 (4.1%) fungi. Streptococci spp. (25, 36.2%) were the most common bacteria, followed by Escherichia coli (18, 26.1%). Nineteen of the 28 gram-negative aerobes (67.9%) were resistant to ciprofloxacin, including 14 of 18 (77.8%) E. coli isolates. When we compared clinical characteristics and treatment outcomes in 17 patients with ciprofloxacin-resistant and 8 with ciprofloxacin-sensitive bacteria, we found that disease duration from diagnosis to drainage (97.2 vs. 50.7 mo, P=0.03) and median length of hospitalization (40 vs. 31 d, P=0.03) was significantly longer in the former. CONCLUSIONS: When gram-negative aerobes were isolated from abscesses in CD patients, more than two thirds were resistant to ciprofloxacin. Providers should consider this high rate of ciprofloxacin resistance when choosing first-line antibiotic treatment for CD-related intra-abdominal abscesses.

Efficacy of linezolid-based salvage therapy compared with glycopeptide-based therapy in patients with persistent methicillin-resistant Staphylococcus aureus bacteremia.

OBJECTIVE: We evaluated the efficacy of linezolid-based salvage therapy compared with glycopeptide-based therapy in patients with persistent (≥7 days) methicillin-resistant Staphylococcus aureus bacteremia (MRSA-B). METHODS: All patients with MRSA-B during 2-year period at a tertiary-care hospital were prospectively enrolled. Linezolid-based salvage therapy was classified if patients switched glycopeptides to linezolid with/without carbapenem due to persistent MRSA-B. Covariate adjustment using the propensity score and inverse probability of treatment weighting (IPTW) using the propensity score were performed to control for bias in treatment assignment. RESULTS: Of 377 patients with MRSA-B, 90 with persistent MRSA-B were included. Of these, 38 (42%) were classified as linezolid-based salvage group and the remaining 52 (58%) as glycopeptide-based therapy group. The duration of persistent bacteremia (median 16 days vs. 10 days; P = 0.008) was longer in linezolid-based salvage group than in the comparator. However, the 30-day mortality (11% vs. 25%; P = 0.08) had a trend toward being lower in linezolid-based salvage group than those in the comparator. Logistic regression models with covariate adjustment and IPTW using propensity scores also revealed that linezolid-based salvage showed a trend toward having better outcome than the comparator, although this did not reach any statistically significance (OR 0.31; 95% CI 0.03-2.95 and OR 0.19; 95% CI 0.01-3.39, respectively). CONCLUSIONS: While having worse prognostic factors compared with glycopeptide-based therapy, linezolid-based salvage therapy revealed a trend toward better outcomes than the comparator. Our data suggest that linezolid-based salvage therapy would be considered in patients with persistent MRSA-B despite the use of glycopeptides therapy.

Emergence of antibiotic resistance during therapy for infections caused by Enterobacteriaceae producing AmpC beta-lactamase: implications for antibiotic use.

Enterobacter spp., Serratia marcescens, Citrobacter freundii, and Morganella morganii are characterized by chromosomally encoded AmpC beta-lactamases and possess the ability to develop resistance upon exposure to broad-spectrum cephalosporins. To determine the incidences of the emergence of resistance during antimicrobial therapy for infections caused by these organisms and the effect of the emergence of resistance on patient outcomes, all patients who were admitted to the Asan Medical Center (Seoul, Republic of Korea) from January 2005 to June 2006 and whose clinical specimens yielded Enterobacter spp., S. marcescens, C. freundii, or M. morganii were monitored prospectively. The main end point was the emergence of resistance during antimicrobial therapy. A total of 732 patients with infections were included for analysis. The overall incidence of the emergence of antimicrobial resistance during antimicrobial therapy was 1.9% (14/732). Resistance to broad-spectrum cephalosporins, cefepime, extended-spectrum penicillin, carbapenem, fluoroquinolones, and aminoglycosides emerged during treatment in 5.0% (11/218), 0% (0/20), 2.0% (2/100), 0% (0/226), 0% (0/153), and 1.1% (1/89) of patients, respectively. The emergence of resistance to broad-spectrum cephalosporins occurred more often in Enterobacter spp. (8.3%, 10/121) than in C. freundii (2.6%, 1/39), S. marcescens (0%, 0/37), or M. morganii (0%, 0/21). Biliary tract infection associated with malignant bile duct invasion was significantly associated with the emergence of resistance to broad-spectrum cephalosporins (P = 0.024 at a significance level of 0.042, by use of the Bonferroni correction). Only 1 of the 14 patients whose isolates developed resistance during antimicrobial therapy died. The emergence of resistance was more frequently associated with broad-spectrum cephalosporins than with the other antimicrobial agents tested, especially in Enterobacter spp. However, the emergence of resistance was associated with a low risk of mortality.