Catherine Liu

Clinical Practice Guidelines by the Infectious Diseases Society of America for the Treatment of Methicillin-Resistant Staphylococcus aureus Infections in Adults and Children

Evidence-based guidelines for the management of patients with methicillin-resistant Staphylococcus aureus (MRSA) infections were prepared by an Expert Panel of the Infectious Diseases Society of America (IDSA). The guidelines are intended for use by health care providers who care for adult and pediatric patients with MRSA infections. The guidelines discuss the management of a variety of clinical syndromes associated with MRSA disease, including skin and soft tissue infections (SSTI), bacteremia and endocarditis, pneumonia, bone and joint infections, and central nervous system (CNS) infections. Recommendations are provided regarding vancomycin dosing and monitoring, management of infections due to MRSA strains with reduced susceptibility to vancomycin, and vancomycin treatment failures.

Staphylococcus aureus with Heterogeneous Resistance to Vancomycin: Epidemiology, Clinical Significance, and Critical Assessment of Diagnostic Methods

The first report of Staphylococcus aureus with intermediate-level resistance to vancomycin (VISA) was from Japan in 1997 (20), raising the threat of incurable staphylococcal infections. Since then, a number of cases have been reported worldwide, with eight confirmed cases in the United States as of June 2002 (9, 13). The majority of these cases have occurred in patients who have had prolonged exposure to vancomycin (13). Furthermore, the majority of these strains appear to have evolved from methicillin-resistant S. aureus (MRSA) strains previously infecting the patient, a conclusion that may be drawn from the similarities observed between the pulsed-field gel electrophoresis patterns of the VISA strains and the preexisting MRSA strains (12, 34). Fortunately, since emerging 6 years ago, infection with VISA is still a rare event. However, the phenomenon of vancomycin heteroresistance in S. aureus (hVISA) has been described more frequently in the literature, although the best method to detect hVISA strains and their clinical significance are ill-defined.

Outcomes from pandemic influenza A H1N1 infection in recipients of solid-organ transplants: a multicentre cohort study

BACKGROUND There are few data on the epidemiology and outcomes of influenza infection in recipients of solid-organ transplants. We aimed to establish the outcomes of pandemic influenza A H1N1 and factors leading to severe disease in a cohort of patients who had received transplants. METHODS We did a multicentre cohort study of adults and children who had received organ transplants with microbiological confirmation of influenza A infection from April to December, 2009. Centres were identified through the American Society of Transplantation Influenza Collaborative Study Group. Demographics, clinical presentation, treatment, and outcomes were assessed. Severity of disease was measured by admission to hospital and intensive care units (ICUs). The data were analysed with descriptive statistics. Proportions were compared by use of chi(2) tests. We used univariate analysis to identify factors leading to pneumonia, admission to hospital, and admission to an ICU. Multivariate analysis was done by use of a stepwise logistic regression model. We analysed deaths with Kaplan-Meier survival analysis. FINDINGS We assessed 237 cases of medically attended influenza A H1N1 reported from 26 transplant centres during the study period. Transplant types included kidney, liver, heart, lung, and others. Both adults (154 patients; median age 47 years) and children (83; 9 years) were assessed. Median time from transplant was 3.6 years. 167 (71%) of 237 patients were admitted to hospital. Data on complications were available for 230 patients; 73 (32%) had pneumonia, 37 (16%) were admitted to ICUs, and ten (4%) died. Antiviral treatment was used in 223 (94%) patients (primarily oseltamivir monotherapy). Seven (8%) patients given antiviral drugs within 48 h of symptom onset were admitted to an ICU compared with 28 (22.4%) given antivirals later (p=0.007). Children who received transplants were less likely to present with pneumonia than adults, but rates of admission to hospital and ICU were similar. INTERPRETATION Influenza A H1N1 caused substantial morbidity in recipients of solid-organ transplants during the 2009-10 pandemic. Starting antiviral therapy early is associated with clinical benefit as measured by need for ICU admission and mechanical ventilation. FUNDING None.

A population-based study of the incidence and molecular epidemiology of methicillin-resistant Staphylococcus aureus disease in San Francisco, 2004-2005.

BACKGROUND Methicillin-resistant Staphylococcus aureus (MRSA) infections have become a major public health problem in both the community and hospitals. Few studies have characterized the incidence and clonal composition of disease-causing strains in an entire population. Our objective was to perform a population-based survey of the clinical and molecular epidemiology of MRSA disease in San Francisco, California. METHODS We prospectively collected 3985 MRSA isolates and associated clinical and demographic information over a 12-month period (2004-2005) at 9 San Francisco-area medical centers. A random sample of 801 isolates was selected for molecular analysis. RESULTS The annual incidence of community-onset MRSA disease among San Francisco residents was 316 cases per 100,000 population, compared with 31 cases per 100,000 population for hospital-onset disease. Persons who were aged 35-44 years, were men, and were black had the highest incidence of community-onset disease. The USA300 MRSA clone accounted for 234 cases of community-onset disease and 15 cases of hospital-onset disease per 100,000 population, constituting an estimated 78.5% and 43.4% of all cases of MRSA disease, respectively. Patients with community-onset USA300 MRSA versus non-USA300 MRSA disease were more likely to be male, be of younger age, and have skin and soft-tissue infections. USA300 strains were generally more susceptible to multiple antibiotics, although decreased susceptibility to tetracycline was observed in both community-onset (P = .008) and hospital-onset (P = .03) USA300 compared to non-USA300 strains. CONCLUSIONS The annual incidence of community-onset MRSA disease in San Francisco is substantial, surpassing that of hospital-onset disease. USA300 is the predominant clone in both the community and hospitals. The dissemination of USA300 from the community into the hospital setting has blurred its distinction as a community-associated pathogen.

Chlamydia Pneumoniae and Atherosclerosis: From Koch Postulates to Clinical Trials

Atherosclerosis is increasingly viewed as an inflammatory process. A number of infectious agents have been implicated in the pathogenesis of coronary artery disease. Chlamydia pneumoniae has been the most popular and well-studied of these pathogens. It is difficult to prove a causal relationship which requires the fulfillment of Kochs postulates, first developed in the late 1800s, to establish an infectious agent as the cause of a disease process. This paper reviews the evidence for and against Chlamydia pneumoniae infection as a contributing factor to atherosclerosis disease. It examines seroepidemiologic and histopathologic studies as well as animal models using Kochs postulates and then provides an analysis of current clinical trial data.

Low colonization prevalence of Staphylococcus aureus with reduced vancomycin susceptibility among patients undergoing hemodialysis in the San Francisco Bay area.

BACKGROUND Staphylococcus aureus exhibits varying degrees of reduced vancomycin susceptibility, and strains with intermediate levels of resistance are thought to emerge by antibiotic selection of subpopulations in heterogeneously resistant precursor strains exposed to this antibiotic. We sought to determine the prevalence of and risk factors for carriage of potential heterogeneous vancomycin-intermediate S. aureus (hVISA). METHODS We prospectively observed a cohort of 211 patients undergoing hemodialysis and performed quarterly surveillance cultures for up to 2 years. We screened for reduced vancomycin susceptibility using brain-heart infusion agar with 4 microg/mL vancomycin. RESULTS We identified 10 colonizing potential hVISA isolates recovered from 7 patients among both methicillin-susceptible and methicillin-resistant S. aureus strains. No confirmed hVISA isolates were identified; we can be 95% certain that the prevalence of confirmed hVISA carriage does not exceed 1.4%. When compared with noncolonized hemodialysis patients, neither vancomycin exposure, duration of hospitalization, nor any baseline clinical or demographic factor was found to predict colonization with potential hVISA on univariate analyses; increased number of months receiving hemodialysis was associated with potential hVISA colonization on multivariate analysis. CONCLUSIONS Despite numerous published reports of S. aureus with reduced vancomycin susceptibility, carriage of these isolates remains a rare phenomenon. Given the unclear clinical significance of potential hVISA, it is not clear whether clinical laboratories should identify such strains, or how they should do so.

Pandemic (H1N1) 2009 Infection in Patients with Hematologic Malignancy

To assess outcomes of patients with hematologic malignancy and pandemic (H1N1) 2009 infection, we reviewed cases during June-December 2009 at the University of California San Francisco Medical Center. Seventeen (63%) and 10 (37%) patients had upper respiratory tract infection (URTI) and lower respiratory tract infection (LRTI), respectively. Cough (85%) and fever (70%) were the most common signs; 19% of patients had nausea, vomiting, or diarrhea. Sixty-five percent of URTI patients were outpatients; 35% recovered without antiviral therapy. All LRTI patients were hospitalized; half required intensive care unit admission. Complications included acute respiratory distress syndrome, pneumomediastinum, myocarditis, and development of oseltamivir-resistant virus; 3 patients died. Of the 3 patients with nosocomial pandemic (H1N1) 2009, 2 died. Pandemic (H1N1) 2009 may cause serious illness in patients with hematologic malignancy, primarily those with LRTI. Rigorous infection control, improved techniques for diagnosing respiratory disease, and early antiviral therapy can prevent nosocomial transmission and optimize patient care.

Detection of vancomycin-intermediate Staphylococcus aureus with the updated Trek-Sensititre System and the MicroScan System. Comparison with results from the conventional Etest and CLSI standardized MIC methods.

Vancomycin-intermediate Staphylococcus aureus (VISA) organisms have minimum inhibitory concentrations (MICs) of 4 to 8 microg/mL and are often associated with vancomycin treatment failure. Detection of VISA has remained problematic. A comparison of 4 methods to detect VISA was done. Of the 20 VISA isolates, the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method yielded susceptible end points of 2 microg/mL for 7, MicroScan (Siemens Healthcare Diagnostics, West Sacramento, CA) for 2, Trek Sensititre (Trek Diagnostic Systems, Cleveland, OH) for 1, and Etest (AB Biodisk North America, Piscataway, NJ) for none. Comparison with the CLSI method showed essential agreement for 95% or more for the Etest, MicroScan, and Trek methods; categorical agreement was as follows: Etest, 60%; MicroScan, 65%; and Trek, 60%. Reliance on a single automated method for determining vancomycin MICs could lead to misclassification of some VISA isolates as vancomycin susceptible. At least 2 methods, including the Etest, should be used when confirming VISA because of slight differences in results from different methods around the end points of 2 and 4 microg/mL .

Discord among Performance Measures for Central Line- Associated Bloodstream Infection

BACKGROUND Central line-associated bloodstream infection (CLABSI) is a national target for mandatory reporting and a Centers for Medicare and Medicaid Services target for value-based purchasing. Differences in chart review versus claims-based metrics used by national agencies and groups raise concerns about the validity of these measures. OBJECTIVE Evaluate consistency and reasons for discordance among chart review and claims-based CLABSI events. METHODS We conducted 2 multicenter retrospective cohort studies within 6 academic institutions. A total of 150 consecutive patients were identified with CLABSI on the basis of National Healthcare Safety Network (NHSN) criteria (NHSN cohort), and an additional 150 consecutive patients were identified with CLABSI on the basis of claims codes (claims cohort). All events had full-text medical record reviews and were identified as concordant or discordant with the other metric. RESULTS In the NHSN cohort, there were 152 CLABSIs among 150 patients, and 73.0% of these cases were discordant with claims data. Common reasons for the lack of associated claims codes included coding omission and lack of physician documentation of bacteremia cause. In the claims cohort, there were 150 CLABSIs among 150 patients, and 65.3% of these cases were discordant with NHSN criteria. Common reasons for the lack of NHSN reporting were identification of non-CLABSI with bacteremia meeting Centers for Disease Control and Prevention (CDC) criteria for an alternative infection source. CONCLUSION Substantial discordance between NHSN and claims-based CLABSI indicators persists. Compared with standardized CDC chart review criteria, claims data often had both coding omissions and misclassification of non-CLABSI infections as CLABSI. Additionally, claims did not identify any additional CLABSIs for CDC reporting. NHSN criteria are a more consistent interhospital standard for CLABSI reporting.

Ertapenem Prophylaxis Associated With an Increased Risk of Clostridium difficile Infection Among Surgical Patients.

A case-control study was conducted to determine risk factors for hospital-onset Clostridium difficile infection among patients admitted to 2 surgical units. Ertapenem prophylaxis was significantly associated with C. difficile infection risk (odds ratio, 3.13 [95% CI, 1.13-8.68], P=.028) and may offer an antimicrobial stewardship target among surgical patients.