MRSA Bloodstream Infections Research Articles

Methicillin-Resistant Staphylococcus aureus and Vancomycin: Minimum Inhibitory Concentration Matters

These investigators found that elevated vancomycin MICs were associated with increased mortality in patients with MRSA infections, a result mostly driven by outcomes of bloodstream infections (BSIs). In contrast, excess mortality in association with elevated MICs was not seen in non-BSI MRSA infections. Among patients with MRSA BSI, although an Etest MIC $2 lg/mL was associated with increased mortality, an Etest MIC of 1.5 lg/mL was not. Throughout the analysis of van Hal

A stick to beat MRSA

Trafford Healthcare NHS Trust's infection control scheme has resulted in more than two years without a case of MRSA bloodstream infection.

Prediction of Failure in Vancomycin-Treated Methicillin-Resistant Staphylococcus aureus Bloodstream Infection: a Clinically Useful Risk Stratification Tool

Methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of bloodstream infection (BSI) and is often associated with invasive infections and high rates of mortality. Vancomycin has remained the mainstay of therapy for serious Gram-positive infections, particularly MRSA BSI; however, therapeutic failures with vancomycin have been increasingly reported. We conducted a comprehensive evaluation of the factors (patient, strain, infection, and treatment) involved in the etiology and management of MRSA BSI to create a risk stratification tool for clinicians. This study included consecutive patients with MRSA BSI treated with vancomycin over 2 years in an inner-city hospital in Detroit, MI. Classification and regression tree analysis (CART) was used to develop a risk prediction model that characterized vancomycin-treated patients at high risk of clinical failure. Of all factors, the Acute Physiology and Chronic Health Evaluation II (APACHE-II) score, with a cutoff point of 14, was found to be the strongest predictor of failure and was used to split the population into two groups. Forty-seven percent of the population had an APACHE-II score < 14, a value that was associated with low rates of clinical failure (11%) and mortality (4%). Fifty-four percent of the population had an APACHE-II score ≥ 14, which was associated with high rates of clinical failure (35%) and mortality (23%). The risk stratification model identified the interplay of three other predictors of failure, including the vancomycin MIC as determined by Vitek 2 analysis, the risk level of the source of BSI, and the USA300 strain type. This model can be a useful tool for clinicians to predict the likelihood of success or failure in vancomycin-treated patients with MRSA bloodstream infection.

Drug-Susceptible S. aureus Still Dangerous

Bruce Jancin is with the Denver bureau of Elsevier Global Medical News. VIENNA – Methicillin-resistant Staphylococcus aureus bloodstream infections grab the headlines and are the focus of many infection-prevention directives, but methicillin-susceptible S. aureus infections, which receive far less attention, have comparable morbidity and mortality, according to two European studies. “MSSA bloodstream infection is MRSA's evil twin,” Michael Laum, MD, said at the European Congress of Clinical Microbiology and Infectious Diseases. He compared key outcomes for 52 patients with MSSA bloodstream infection and 16 with MRSA bloodstream infection at Blackpool Victoria Hospital in Lancashire, England, during a 20-month period starting in November 2007. There were far fewer cases of MRSA infection because incidence plunged by 78% in the year after the hospital introduced a comprehensive MRSA containment program. The average length of stay was 23.2 days for patients with MSSA infection and 26.3 days with MRSA. The MSSA patients averaged 61 years of age, the MRSA patients 71. Eighteen percent of MSSA patients were admitted to intensive care, as were 19% with MRSA. In-hospital mortality was 34% in the MSSA patients and 44% in the MRSA group. The average Acute Physiology and Chronic Health Evaluation (APACHE) II score at the time blood cultures were obtained was 13 points in the MSSA group and 16 for the MRSA patients. Eighty-four percent of the MSSA patients had optimal antibiotics initiated before their blood culture results were known, as did just 54% of those with MRSA. Seventy-one percent of MSSA infections and 80% of MRSA infections had their onset less than 48 hours after patient hospitalization, strongly suggesting community-acquired infection. The lesson of the study is mandatory MRSA screening and surveillance program ought to be expanded to incorporate MSSA, concluded Dr. Lau of the hospital's general surgery department. A similar point was made in the Burden of Resistance and Disease in European Nations (BURDEN) study presented by Marlieke de Kraker of the National Institute for Public Health and the Environment, Bilthoven, the Netherlands. BURDEN included all adult patients with MRSA or MSSA bloodstream infection at a tertiary care hospital in each of 13 European countries during a 1-year period. The study population comprised 248 patients with MRSA and 453 controls matched for age, Charlson Comorbidity Index score, and duration of hospital stay before infection, along with 618 patients with MSSA and 1,170 matched controls. Patients with MSSA often present with a different clinical picture than do those with MRSA, Ms. de Kraker said. Patients with MRSA infection tend to be older and have more comorbidities. In-hospital mortality occurred in 36% of the MRSA group and 9% of their controls, and in 23% of the MSSA group and 7% of their controls. In a multivariate analysis, MRSA infection was associated with a 3.5-fold increased risk of in-hospital mortality, and MSSA carried a 3.1-fold increased mortality risk compared with controls. Another multivariate analysis demonstrated that bloodstream infection with MRSA added an average of 9.2 days to the length of a hospital stay, while MSSA resulted in an extra 8.6 days, she reported. “The burden of S. aureus bloodstream infections in the hospital is high, for MRSA as well as MSSA. Methicillin resistance does not seem to be associated with excess length of stay or mortality. Infection prevention should be aimed at decreasing the number of S. aureus bloodstream infections, irrespective of methicillin susceptibility,” Ms. de Kraker said. Dr. Lau and Ms. de Kraker each reported having no financial conflict.

Carriage of Community-Associated Methicillin-Resistant Staphylococcus aureus in a Cohort of Infants in Southern Israel: Risk Factors and Molecular Features

There are few data about the epidemiology of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) among children in Israel. This study was intended to identify risk factors for CA-MRSA colonization in healthy infants, to characterize the molecular features of colonizing organisms, and to determine whether they are responsible for health care-associated (HA) infections. Nasal cultures and demographic details were collected from a cohort of healthy infants at 5 visits between the ages of 2 and 12 months. Clinical characteristics of pediatric MRSA bloodstream infections (2001 to 2006) and wound cultures collected over 6 months were also studied. Clonal structure was evaluated by multilocus sequence typing. Isolates were studied for the staphylococcal cassette chromosome mec (SCCmec) type and for the presence of Panton-Valentine leukocidin (PVL) genes. MRSA was cultured at least once from 45 of 659 infants (346 Jewish and 313 Bedouin infants). Forty of 45 (89%) isolates were from Bedouin infants. Twenty-nine of 45 (64.4%) belonged to a new clonal complex, designated CC913, that carries SCCmec IV but not the PVL genes. CC913 was also isolated from 9/14 blood cultures and 7/8 wounds. All CC913 infections occurred in Bedouin children, and all but two were HA. In conclusion, Bedouin origin was the main risk factor for carriage of CA-MRSA. CC913 was dominant both in healthy carriers and as a cause of pediatric HA-MRSA bloodstream infections.

Emergence of Community-Associated Methicillin-ResistantStaphylococcus aureusStrains as a Cause of Healthcare-Associated Bloodstream Infections in Korea

The prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains causing bloodstream infection (BSI) has not been studied in Korea. 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. 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. 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. 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.

Investigating an Increase in Methicillin Resistant Staphyloccus aurues (MRSA) Infections in a Free Standing Outpatient Hemodialysis Center

BACKGROUND/OBJECTIVES: In September of 2006, 3 MRSA positive blood stream infections (BSI) were identified among the chronic hemodialysis patients at Barnes-Jewish Dialysis Center. Despite dialysis patients being at high risk for MRSA, there had only been 2 identified MRSA BSI's in the previous 12 months. Because hemodialysis patients are at higher risk for serious comobidities and prolonged colonization following a MRSA infection, surveillance cultures on the entire dialysis center population were obtained in October of 2006.

Staphylococcus aureus Strains Isolated from Bloodstream Infections Changed Significantly in 2006

We studied 358 Staphylococcus aureus strains isolated from bloodstream infections (BSI) observed during an epidemiological study covering 2,007,681 days of hospitalization in 32 healthcare institutions (HCIs) between 2004 and 2006. The strains were tested for antibiotic susceptibility and characterized genetically. The incidence of S. aureus BSI declined regularly through 2004 and 2005 and then significantly increased in 2006 (+80%). This was largely due to an increase in BSI involving methicillin-sensitive S. aureus (MSSA) strains and nonmultiresistant methicillin-resistant S. aureus (NORSA) strains. Ninety-six percent of the NORSA strains were resistant only to methicillin and fluoroquinolones. Most of the MSSA strains belonged to a small number of pulsed-field gel electrophoresis (PFGE) divisions and were associated with epidemic phenomena in HCIs. The NORSA strains also clustered into a limited number of PFGE divisions but could not be related to any local outbreak in HCIs. In 2006, there was a significant increase in the incidence of BSI associated with tst gene-positive MSSA strains (+275%) and the first three BSI associated with tst gene-positive MRSA were observed. PFGE data revealed a limited heterogeneity among the tst gene-positive strains without any outbreak in the HCIs. Our study underlines the need for infection control teams to focus efforts on preventing both MRSA and MSSA BSI. As recently demonstrated in vitro, fluoroquinolones may enhance horizontal transfer of virulence and antibiotic resistance genes. These antibiotics are widely used in France, so our findings raise the issue of whether their use has contributed to the acquisition of mecA and tst genes by S. aureus strains.

Correlation between reduced susceptibility to vancomycin and clinical outcome in MRSA blood stream infections

Correlation between reduced susceptibility to vancomycin and clinical outcome in MRSA blood stream infections

Determinants of vancomycin use in adult intensive care units in 41 United States hospitals.

We analyzed data from a prospective observational cohort study that included 108 adult intensive care units (ICUs) in 41 United States hospitals. Use of vancomycin (defined daily doses per 1,000 patient-days), nosocomial infection rates, and proportion of all Staphylococcus aureus isolates resistant to methicillin (MRSA rate) were recorded from January 1996 through November 1997. The median rate of vancomycin use was lowest in coronary care ICUs and highest in general surgical ICUs. Prior approval before use of vancomycin was required in only 26 (24%) of the 108 ICUs. In a multivariate linear regression model, rates of MRSA, central line-associated bloodstream infection, and the type of ICU were independent predictors of vancomycin use. None of the vancomycin control practices was associated with lower rates of vancomycin use; however, it is important to recognize that this database was not designed to measure rates of inappropriate use. Vancomycin use is heavily determined by rates of endemic MRSA and central line-associated bloodstream infection. Efforts to reduce these rates through infection control activities should be included in hospitals' efforts to reduce vancomycin use.