Wan-Shik Shin

Emergence of Community‐Associated Methicillin‐Resistant Staphylococcus aureus Strains as a Cause of Healthcare‐Associated Bloodstream Infections in Korea

BACKGROUND The prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains causing bloodstream infection (BSI) has not been studied in Korea. OBJECTIVE We sought to determine the prevalence of CA-MRSA strains among isolates recovered from patients with MRSA BSIs and to explore epidemiological changes in Korea. We also sought to evaluate clinical characteristics relevant to the development of healthcare-associated BSIs. METHODS We prospectively collected consecutive MRSA isolates from patients with BSI at 4 hospitals from July 1 through November 30, 2007, and we also included MRSA isolates recovered from culture of blood samples collected during a previous year (October 1, 2004 through September 30, 2005) at a different hospital. Molecular typing studies were performed, including pulsed-field gel electrophoresis (PFGE), multilocus sequence typing, Staphylococcus protein A (spa) typing, and staphylococcal cassette chromosome mec (SCCmec) typing. We compared the clinical characteristics and outcomes of patients with healthcare-associated BSI due to CA-MRSA strains with those of patients with healthcare-associated BSI due to healthcare-associated MRSA (HA-MRSA) strains. RESULTS There were 76 cases of MRSA BSI, of which 4 (5.3%) were community-associated and 72 (94.7%) were healthcare-associated. Among the 72 HA-MRSA BSIs, 18 (25%) were community onset, and 54 (75%) were hospital onset. PFGE type D-ST72-spa B-SCCmec type IVA MRSA, the predominant genotype of CA-MRSA in Korea, accounted for 19 (25%) of all 76 MRSA BSIs, including 17 (23.6%) of 72 HA-MRSA BSIs and 11 (20.8%) of 53 hospital-onset HA-MRSA BSIs. Patients with healthcare-associated BSIs due to CA-MRSA strains carrying SCCmec type IVA tended to have fewer healthcare-associated risk factors, compared with patients with healthcare-associated BSIs due to HA-MRSA strains carrying other SCCmec types. The presence of a central venous catheter or other invasive device was the only independent factor differentiating patients infected with hospital-associated genotype strains from patients infected with other strains. Clinical outcomes were similar between both groups. CONCLUSIONS CA-MRSA strains are emerging as a major cause of BSI in healthcare settings in Korea. This changing epidemiology of MRSA poses a challenge to public health and infection control in hospital settings.

Application of Nucleic Acid Sequence–Based Amplification for Diagnosis of and Monitoring the Clinical Course of Invasive Aspergillosis in Patients with Hematologic Diseases

BACKGROUND AND METHODS We evaluated nucleic acid sequence-based amplification (NASBA) and a galactomannan enzyme immunosorbent assay (GM-EIA) for the diagnosis of invasive aspergillosis (IA) in neutropenic febrile patients and for monitoring of its clinical course and outcome. Blood samples were collected twice per week from 128 patients with hematologic diseases during periods of neutropenic fever after undergoing chemotherapy or hematopoietic stem cell transplantation. A total of 448 blood samples were tested. RESULTS There were 14 patients with IA (2 patients with proven IA and 12 with probable IA). The median index of the initial NASBA in the IA group was more than 10-fold higher than that in the non-IA group. Galactomannan antigenemia (index, >0.5) was detected with a sensitivity of 86%. In receiver-operator characteristic analysis, the cutoff index of NASBA for the presumptive diagnosis of IA was determined to be 5.0. Combination of these 2 parameters (either a GM-EIA index of >or=0.5 or a NASBA index of >or=5.0) improved the sensitivity of diagnosis to 100%. There was a close relationship between patient outcome and the kinetics of NASBA values: failure of negative conversion during treatment resulted in death in almost all cases. CONCLUSION If either GM-EIA or NASBA results suggest IA, the diagnostic yield for IA could be improved, and NASBA could be a useful marker for predicting the clinical course and outcome of treatment.

In vitro effects of ciprofloxacin and roxithromycin on apoptosis of jurkat T lymphocytes.

ABSTRACT Ciprofloxacin (CPFX) and roxithromycin (RXM) induced apoptosis of activated Jurkat T cells in vitro. CPFX showed concentration-dependent acceleration of apoptosis of activated Jurkat T cells by enhancing the expression of FasL and activities of caspase-3 and -8. RXM accelerated cell death, enhanced expression of FasL and caspase-3 but not caspase-8, and did not show the concentration dependency.

Effect of Moxifloxacin on Production of Proinflammatory Cytokines from Human Peripheral Blood Mononuclear Cells

ABSTRACT The effects of moxifloxacin, a new methoxyfluoroquinolone, on the production of proinflammatory cytokines from human peripheral blood mononuclear cells (PBMCs) were evaluated. Moxifloxacin inhibited the production of tumor necrosis factor alpha (TNF-α) and/or interleukin-6 (IL-6) by PBMCs stimulated with lipopolysaccharide (LPS), lipoteichoic acid (LTA), and heat-killed bacteria in a concentration-dependent manner without cytotoxic effects. The addition of moxifloxacin reduced the population of cells positive for CD-14 and TNF-α and for CD-14 and IL-6 among the LPS- or LTA-stimulated PBMCs. By Western blot analysis, moxifloxacin pretreatment reduced the degradation of IκBα in LPS-stimulated PBMCs. In conclusion, moxifloxacin could interfere with NF-κB activation by inhibiting the degradation of IκBα and reduce the levels of production of proinflammatory cytokines.

Comparison of Quantitative Cytomegalovirus Real-time PCR in Whole Blood and pp65 Antigenemia Assay: Clinical Utility of CMV Real-time PCR in Hematopoietic Stem Cell Transplant Recipients

Successful preemptive therapy for cytomegalovirus (CMV) infection in transplant patients depends on the availability of sensitive, specific, and timely diagnostic tests for CMV infection. Although the pp65 antigenemia assay has been widely used for this purpose, real-time quantification of CMV DNA has recently been recognized as an alternative diagnostic approach. However, the guidelines for antiviral therapy based on real-time quantitative polymerase chain reaction (RQ-PCR) have yet to be established. From November 2004 to March 2005, a total of 555 whole blood samples from 131 hematopoietic stem cell transplant (HSCT) recipients were prospectively collected. RQ-PCR was conducted using an Artus® CMV LC PCR kit (QIAGEN). Both qualitative and quantitative correlations were drawn between the two methods. Exposure to the antiviral agent influenced the results of the two assays. Additionally, the discrepancy was observed at low levels of antigenemia and CMV DNA load. Via ROC curve analysis, the tentative cutoff value for preemptive therapy was determined to be approximately 2×104 copies/mL (sensitivity, 80.0%; specificity, 50.0%) in the high risk patients, and approximately 3×104 copies/mL (sensitivity, 90.0%; specificity, 70.0%) in the patients at low risk for CMV disease. Further study to validate the optimal cutoff value for the initiation of preemptive therapy is currently underway.

Molecular Epidemiological Analysis of Quinolone-Resistant Escherichia coli Causing Bacteremia in Neutropenic Patients with Leukemia in Korea

We analyzed an outbreak of Escherichia coli bacteremia in eight patients with leukemia in a hematology-oncology unit from July to September 1994. The antibiograms and genotypic patterns of the isolates were different, thus suggesting that the outbreak did not originate from a single clone. However, all the isolates were resistant to quinolones, which led us to examine the microbiological records from 1992 to 1994. The incidence of quinolone-resistant E. coli bacteremia in the hematology-oncology unit ranged from 81.8% to 94.6% during this period. We then analyzed 36 more isolates recovered from late 1994 to 1995. Field inversion gel electrophoresis patterns of these isolates were also different. Analysis of the quinolone resistance determining region in gyrA revealed that all the isolates had a double mutation in gyrA. In conclusion, quinolone-resistant E. coli could be an emerging threat to neutropenic patients with leukemia who receive a quinolone prophylactically, and attention must be paid to this trend of resistance.

Risk-Adapted Preemptive Therapy for Cytomegalovirus Disease after Allogeneic Stem Cell Transplantation: A Single-Center Experience in Korea

Cytomegalovirus (CMV) remains a major cause of infection in recipients of hematopoietic stem cell transplants (HSCT) and results in significant mortality and morbidity. We present the results of CMV pp65 antigenemia-guided, risk-adapted preemptive therapy aimed at preventing CMV disease in allogeneic HSCT. Preemptive ganciclovir treatment was started when more than 5 CMV antigen-positive cells were detected in the low-risk group (with grade 0-I acute GVHD and matched related HSCT) and when any antigen-positive cells were seen in the high-risk group (with grade II-IV acute GVHD or matched unrelated HSCT). At least 1 episode of antigenemia was observed in 53 (59.6%) of 89 patients before day 100, and preemptive therapy was performed in 33 patients. CMV disease occurred in 6 patients (5 in the high-risk group and 1 in the low-risk group), and late CMV disease developed in 4 patients. Only 1 patient died of CMV pneumonitis before day 100. Neutropenia was observed in 51.5% of ganciclovir-treated patients, and coinfection/superinfection was observed in 42.4%. A strategy of ganciclovir treatment focusing on patients at higher risk could reduce the toxicity from the antiviral drug and be cost-effective. Extended surveillance for CMV disease using more sensitive diagnostic methods is necessary in high-risk patients.

Efficacies of Vancomycin, Arbekacin, and Gentamicin Alone or in Combination against Methicillin-Resistant Staphylococcus aureus in an In Vitro Infective Endocarditis Model

ABSTRACT We adopted an in vitro infective endocarditis model (IVIEM) to compare the efficacy of vancomycin (VAN), arbekacin (ABK), and gentamicin (GEN) alone or in combination. Using two strains of clinically isolated methicillin-resistant Staphylococcus aureus, one GEN susceptible (GS171) and one GEN resistant (GR153), fibrin clots were prepared and suspended in the IVIEM. Antibiotics were given as boluses every 6 h (q6h), q12h, or q24h or by continuous infusion with VAN, q12h or q24h with ABK, and q8h or q24h with GEN. For combination treatment, VAN q12h plus ABK q24h and VAN q12h plus GEN q24h were given. Fibrin clots were removed from each model at 0, 8, 24, 32, 48, and 72 h, and the bacterial densities were determined. The number of colonies within the fibrin clot was significantly decreased in all study groups compared with control groups (P < 0.001). When VAN and ABK were administered alone, the number of colonies was significantly lower in GS171 than in GR153 by 8 h after administration (P = 0.02) and was lowest in GS171 when ABK was administered q12h (P = 0.01). At 72 h, ABK or VAN alone produced equivalent bacterial reductions regardless of dosing frequency and GEN resistance. In GR153, VAN plus ABK showed an additive effect till 24 h, although VAN plus GEN showed indifference. Our data suggest that ABK could be used as an alternative to VAN in GEN-resistant staphylococcal endocarditis. An additive effect was seen when VAN and ABK were used together in GEN-resistant strains until 24 h; however, further studies are warranted for the clinical application of this combination.

Prognostic Factors Influencing Infection-related Mortality in Patients with Acute Leukemia in Korea

We retrospectively reviewed the medical records of 284 patients with neutropenic fever following chemotherapy for acute leukemia at the Catholic Hematopoietic Stem Cell Transplantation Center from January 1998 to December 1999, to identify prognostic factors for infection related mortality. Twenty-eight patients died of infections. There was no difference in median age, gender ratio, or underlying disease between the dying and surviving groups. Bacteria were the main pathogens following chemotherapy, and Gram positive organisms predominated in the dying group. Pneumonia and sepsis were the main causes of death. There were 72 cases of invasive fungal infection and their mortality was 27.8%. Invasive fungal infection and previous history of fungal infection were independent prognostic factors for outcome. Recovery from neutropenia was the significant protective factor for mortality. In conclusion, the prognostic factors identified in this study could be useful for deciding on more intensive treatment for those patients at greater risk of death. To our knowledge, this is the first Korean study delineating prognostic factors in acute leukemic patients with infectious complications.

Comparison of the Real-time Nucleic Acid Sequence-based Amplification (RTi-NASBA) with Conventional NASBA, and Galactomannan Assay for the Diagnosis of Invasive Aspergillosis

We compared a real time-nucleic acid sequence-based amplification (RTi-NASBA) with conventional NASBA, galactomannan enzyme immunosorbent assay (GM-EIA), and Mycology Study Group of the European Organization for Research and Treatment of Cancer (EORTC/MSG) criteria for the diagnosis of invasive aspergillosis (IA). From May 2004 to May 2005, blood samples (314 in total) were collected twice a week from 78 patients with hematologic diseases during neutropenic fever after chemotherapy or hematopoietic stem cell transplantation. Results were compared with each other on the basis of EORTC/ MSG criteria. The cutoff of conventional NASBA was set to be 3.5; GM 0.5; RTi-NASBA, 20% above the negative control. There were 22 patients with IA (7 probables and 15 possibles) and 56 patients with nonfungal infection. The Kappa statistic for RTi-NASBA versus conventional NASBA was 0.80 (0.66-0.82; p<0.001) indicating that there was fairly good accordance between two tests. RTi-NASBA showed sensitivity 0.96, specificity 0.43, positive- and negative-predictive value 0.40 and 0.96, respectively. GM showed good specificity (0.98), while the sensitivity (0.45) was poor. When we use the combination of GM with either of two NASBAs, the sensitivity was improved up to 100%. In conclusion, RTi-NASBA could be a good alternative to the conventional one for the screening of IA.