Staphylococcus aureus bacteremia at 5 US academic medical centers, 2008-2011: significant geographic variation in community-onset infections

Reduced Vancomycin Susceptibility of Methicillin-Susceptible Staphylococcus aureus Has No Significant Impact on Mortality but Results in an Increase in Complicated Infection

Methicillin-susceptible Staphylococcus aureus (MSSA) bloodstream infections (BSIs) often lead to severe complications despite the availability of effective antibiotics. It remains unclear whether elevated vancomycin MICs are associated with worse outcomes. We conducted a 2-year retrospective cohort study (n = 252) of patients with MSSA BSIs at a tertiary care hospital. We defined reduced vancomycin susceptibility (RVS) as a Microscan MIC of 2 mg/liter. All strains were genotyped (spa) and assessed for agr functionality. Multivariable logistic regression models were used to examine the impact of RVS phenotype and strain genotype on 30-day all-cause mortality and complicated bacteremia (metastatic spread, endovascular infection, or duration ≥3 days). One-third of patients (84/252) were infected with RVS isolates. RVS Infections were more frequently associated with metastatic or embolic sites of infection (36% versus 17%, P < 0.001), and endovascular infection (26% versus 12%, P = 0.004). These infections occurred more often in patients with fewer underlying comorbidities (Charlson comorbidity index of ≥3 [73% versus 88%, P = 0.002]). Genotyping identified 127 spa-types and 14 Spa-clonal complexes (Spa-CCs). Spa-CC002 and Spa-CC008 were more likely to exhibit the RVS phenotype versus other Spa-CCs (OR = 2.2, P < 0.01). The RVS phenotype was not significantly associated with 30-day mortality; however, it was associated with complicated bacteremia (adjusted odds ratio of 2.35 [range, 1.26 to 4.37]; P = 0.007) in adjusted analyses. The association of RVS strains with complicated infection and fewer underlying comorbidities suggests the phenotype as a potential marker of strain virulence in MSSA BSIs. The RVS phenotype itself was not a significant predictor of mortality in this patient cohort. Further studies are necessary to explore this host-pathogen relationship.

Life After USA300: The Rise and Fall of a Superbug

The community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) epidemic in the United States is largely attributable to the meteoric rise of a single clone, referred to as USA300. This strain not only spread across the United States in just a few years to become the predominant cause of staphylococcal disease, but it also appears to have increased the overall number of skin and soft-tissue infections (SSTIs), increasing the overall disease burden. While USA300 still constitutes a major public health burden, its prevalence may be decreasing in some parts of the United States. Other than an epidemic in South America due to a closely related strain, USA300 also seems to have been largely unable to establish itself as an endemic infection in other geographic locations. While there have been several hypotheses put forward to explain the enormous success of USA300, the reasons for its failures and its potential fall remain obscure. Far from being unique to USA300, the rise and fall of specific clones of S. aureus in human populations seems to be a common process that has occurred multiple times and in multiple locations. This review charts the rise of USA300 and the evidence that suggests that it may be in decline, and it considers how best to understand the future spread, containment, and possible extinction of CA-MRSA.

Implementation of a cefazolin-based stewardship pathway for methicillin-susceptible Staphylococcus aureus bloodstream infections paired with infectious diseases consultation

Methicillin-susceptible Staphylococcus aureus (MSSA) infections have been successfully treated both with cefazolin and antistaphylococcal penicillins; cefazolin appears effective in MSSA bloodstream infections (BSIs). Thus, our antimicrobial stewardship programme (ASP) implemented a clinical pathway supporting cefazolin use in MSSA-BSIs and restricting oxacillin use to infectious diseases (ID) consultation due to cefazolin's lower cost and more convenient dosing. This before and after quasi-experimental study was conducted to describe the impact on outcomes and process of care measures associated with implementing this pathway among patients with MSSA-BSI. Definitive treatment with cefazolin increased over the study period from 17.3% to 69.8% post-implementation. Clinical failure (5.8% vs. 2.3%; P = 0.62) and in-hospital mortality (3.8% vs. 0%; P = 0.50) were rare pre- and post-implementation. Median hospital length of stay among survivors was similar between pre- and post-implementation periods (P = 0.31). Duration of bacteraemia [median (IQR) 3 (2-4) days vs. 2 (2-3) days; P = 0.002] and rates of re-infection after culture clearance (9.6% vs. 0%; P = 0.06) were reduced post-implementation. Frequency of source control (P = 0.71) and time to source control (P = 0.52) were similar between study periods. Significant increases in ID consultations (33.3% [3/9] vs. 73.3% [22/30]; P = 0.047) and median (IQR) 24-h daily doses [2 (1-3) g vs. 6 (3-6) g; P < 0.01] were seen for patients treated with cefazolin post-implementation. ASPs may find implementation of a similar pathway to be an effective means of improving the care of patients infected with MSSA.

Paediatric Staphylococcus aureus bacteraemia: A single-centre retrospective cohort

AIM

We aimed to describe the clinical epidemiology of Staphylococcus aureus bacteraemia (SAB) at a large, tertiary/quaternary children's hospital in Australia.

METHODS

We performed a retrospective chart review of SAB cases at the Children's Hospital at Westmead (CHW) over 5 years; 2006-2011. We compared frequency, clinical profile and outcomes of SAB with published data from CHW; 1994-1998. We compared health-care associated with community-associated (HCA-SAB and CA-SAB; defined epidemiologically) and methicillin-resistant with methicillin susceptible S. aureus (MRSA and MSSA).

RESULTS

We identified 174 episodes of paediatric SAB with an average annual admission rate of 1.3/1000 which has not increased compared with a decade earlier. Half of the cases (49%) were CA-SAB; 18% were MRSA. The proportion of CA-MRSA bacteraemia (22%) has increased. The proportion of SAB associated with central venous access devices (CVADs; 40%) has increased. CA-SAB cases were more likely to present with a tissue focus of disease (e.g. osteo-articular, pneumonia) and often required surgery. HCA-SAB less frequently required surgery, a minority is MRSA, and vascular device intervention (removal, sterilisation) is common. Six cases (4%) of infective endocarditis (IE) were identified; three with a history of congenital heart disease, two with CVADs in situ. There were no deaths in this cohort.

CONCLUSIONS

Over an 18-year period, the proportion of SAB due to CA-MRSA and SAB associated with CVADs has increased. Categorisation of SAB as HCA and CA reveals two broad phenotypes of paediatric SAB. SAB in children is infrequently associated with IE. The health-care burden of paediatric SAB is considerable', but mortality is low.

Treatment of Staphylococcus aureus Infections

Staphylococcus aureus, although generally identified as a commensal, is also a common cause of human bacterial infections, including of the skin and other soft tissues, bones, bloodstream, and respiratory tract. The history of S. aureus treatment is marked by the development of resistance to each new class of antistaphylococcal antimicrobial drugs, including the penicillins, sulfonamides, tetracyclines, glycopeptides, and others, complicating therapy. S. aureus isolates identified in the 1960s were sometimes resistant to methicillin, a ß-lactam antimicrobial active initially against a majority S. aureus strains. These MRSA isolates, resistant to nearly all ß-lactam antimicrobials, were first largely confined to the health care environment and the patients who attended it. However, in the mid-1990s, new strains, known as community-associated (CA-) MRSA strains, emerged. CA-MRSA organisms, compared with health care-associated (HA-) MRSA strain types, are more often susceptible to multiple classes of non ß-lactam antimicrobials. While infections caused by methicillin-susceptible S. aureus (MSSA) strains are usually treated with drugs in the ß-lactam class, such as cephalosporins, oxacillin or nafcillin, MRSA infections are treated with drugs in other antimicrobial classes. The glycopeptide drug vancomycin, and in some countries teicoplanin, is the most common drug used to treat severe MRSA infections. There are now other classes of antimicrobials available to treat staphylococcal infections, including several that have been approved after 2009. The antimicrobial management of invasive and noninvasive S. aureus infections in the ambulatory and in-patient settings is the topic of this review. Also discussed are common adverse effects of antistaphylococcal antimicrobial agents, advantages of one agent over another for specific clinical syndromes, and the use of adjunctive therapies such as surgery and intravenous immunoglobulin. We have detailed considerations in the therapy of noninvasive and invasive S. aureus infections. This is followed by sections on specific clinical infectious syndromes including skin and soft tissue infections, bacteremia, endocarditis and intravascular infections, pneumonia, osteomyelitis and vertebral discitis, epidural abscess, septic arthritis, pyomyositis, mastitis, necrotizing fasciitis, orbital infections, endophthalmitis, parotitis, staphylococcal toxinoses, urogenital infections, and central nervous system infections.

Safety of Dalbavancin in the Treatment of Skin and Skin Structure Infections: A Pooled Analysis of Randomized, Comparative Studies

Introduction

Dalbavancin is a new lipoglycopeptide that is active against Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus. It has a half-life of 14.4 days, permitting intravenous treatment of acute bacterial skin and skin structure infections without the need for daily dosing.

Objective

The objective of these analyses was to compare the adverse event profile of dalbavancin with that of the comparator agents in the treatment of skin and skin structure infections.

Methods

Data on adverse events and laboratory assessments collected from 3002 patients enrolled in seven late-stage, randomized clinical trials were analyzed for patients receiving dalbavancin or a comparator antibiotic.

Results

Overall adverse event rates were similar or lower for patients receiving dalbavancin (799/1778; 44.9 %) compared with those receiving comparator agents (573/1224; 46.8 %, p = 0.012). The most common treatment-emergent adverse events were nausea, headache, diarrhea, constipation, vomiting, rash, urinary tract infection, pruritus, and insomnia. The duration and timing of the onset of adverse events were similar for patients receiving dalbavancin relative to the comparators.

Conclusion

Dalbavancin exhibits a favorable overall safety profile for treatment of acute bacterial skin and skin structure infections due to Gram-positive bacteria.

The Impact of Reporting a Prior Penicillin Allergy on the Treatment of Methicillin-Sensitive Staphylococcus aureus Bacteremia

BACKGROUND

Methicillin-sensitive Staphylococcus aureus (MSSA) bacteremia is a morbid infection with mortality benefit from receipt of parenteral β-lactam therapy. A substantial portion of MSSA bacteremia patients report penicillin allergy, but infrequently have true allergy.

OBJECTIVE

To determine the frequency and predictors of optimal and adequate therapy in patients with MSSA bacteremia.

DESIGN

Retrospective cohort.

PARTICIPANTS

Adult inpatients with MSSA bacteremia, January 2009 through October 2013.

MAIN MEASURES

The primary measure was a trial of optimal therapy (OT), defined as ≥3 inpatient days or discharge on any first-line agents (nafcillin, oxacillin, cefazolin, or penicillin G, if susceptible). The secondary measure was completion of adequate therapy (AT), defined as ≥10 inpatient days or discharge on an agent appropriate for MSSA bacteremia. Data were electronically gathered with key variables manually validated through chart review. Log-binomial regression models were used to determine the frequency and predictors of outcomes.

KEY RESULTS

Of 456 patients, 346 (76%) received a trial of OT. Patients reporting penicillin allergy (13%) were less likely to receive OT trial than those without penicillin allergy (47% vs. 80%, p <0.001). Adjusting for other factors, penicillin allergy was the largest negative predictor of OT trial (RR 0.64 [0.49, 0.83]). Infectious Disease (ID) consultation was the largest positive predictor of OT trial across all patients (RR 1.34 [1.14, 1.57]). Allergy/Immunology consultation was the single most important predictor of OT trial among patients reporting penicillin allergy (RR 2.33 [1.44, 3.77]). Of 440 patients, 391 (89%) completed AT, with ID consultation the largest positive predictor of the outcome (RR 1.28 [1.15, 1.43]).

CONCLUSIONS

Nearly 25% of patients with MSSA bacteremia did not receive OT trial and about 10% did not receive AT completion. Reported penicillin allergy reduced, and ID consult increased, the likelihood of OT. Allergy evaluation, coupled with ID consultation, may improve outcomes in MSSA bacteremic patients.

Time trends in Staphylococcus aureus bacteremia, 1988-2010, in a tertiary center with high methicillin resistance rates

INTRODUCTION

Changes in the epidemiology of Staphylococcus aureus bacteremia (SAB) have been described in recent decades. Decreased mortality has been reported over time, mostly from countries with low methicillin resistance rates. We aimed to describe time trends in SAB in a tertiary center with high methicillin resistance rates.

METHODS

We retrospectively analyzed 1692 patients with SAB, and compared between three time periods: 1988-1994 (342 patients), 1998-2004 (597 patients) and 2005-2010 (753 patients).

RESULTS

In our cohort, 30 days mortality increased significantly with time, reaching 42.9 % during 2005-2010. The latter period was characterized by higher rates of older patients (35.1 % aged 80 years and older), with lower functional capacity (46.5 % bedridden) and higher rates of comorbidities (33.6 % renal disease, 24.8 % heart failure, 19.0 % dementia). These patients were more likely to be ventilated (18.7 %) and carry a urinary catheter at presentation (46.6 %); present with septic shock (15.9 %) and have pneumonia (20.5 %) or endocarditis (7.2 %) as source. Similar characteristics were found among patients younger than 50 years and with independent functional status. No significant increase in methicillin resistant Staph aureus (MRSA) rates or inappropriate empirical therapy was demonstrated during 2005-2010.

CONCLUSIONS

In our cohort, increased mortality in recent years in patients with SAB can be explained by baseline condition of patients. MRSA or inappropriate empiric therapy did not explain the increase in mortality. The patients afflicted with SAB changed over time. Epidemiology and outcomes of SAB vary with time and according to geographical location. External validity of studies should be taken into consideration.

National Bloodstream Infection Surveillance in Switzerland 2008-2014: Different Patterns and Trends for University and Community Hospitals

OBJECTIVE To characterize the epidemiology of bloodstream infections in Switzerland, comparing selected pathogens in community and university hospitals. DESIGN Observational, retrospective, multicenter laboratory surveillance study. METHODS Data on bloodstream infections from 2008 through 2014 were obtained from the Swiss infection surveillance system, which is part of the Swiss Centre for Antibiotic Resistance (ANRESIS). We compared pathogen prevalences across 26 acute care hospitals. A subanalysis for community-acquired and hospital-acquired bloodstream infections in community and university hospitals was performed. RESULTS A total of 42,802 bloodstream infection episodes were analyzed. The most common etiologies were Escherichia coli (28.3%), Staphylococcus aureus (12.4%), and polymicrobial bloodstream infections (11.4%). The proportion of E. coli increased from 27.5% in 2008 to 29.6% in 2014 (P = .04). E. coli and S. aureus were more commonly reported in community than university hospitals (34.3% vs 22.7%, P<.001 and 13.9% vs 11.1%, P<.001, respectively). Fifty percent of episodes were community-acquired, with E. coli again being more common in community hospitals (41.0% vs 32.4%, P<.001). The proportion of E. coli in community-acquired bloodstream infections increased in community hospitals only. Community-acquired polymicrobial infections (9.9% vs 5.6%, P<.001) and community-acquired coagulase-negative staphylococci (6.7% vs 3.4%, P<0.001) were more prevalent in university hospitals. CONCLUSIONS The role of E. coli as predominant pathogen in bloodstream infections has become more pronounced. There are distinct patterns in community and university hospitals, potentially influencing empirical antibiotic treatment. Infect Control Hosp Epidemiol 2016;37:1060-1067.

Changing Susceptibility of Staphylococcus aureus in a US Pediatric Population

BACKGROUND

Staphylococcus aureus is a major cause of infection in both adult and pediatric populations. After several decades of increasing prevalence, the proportion of S aureus infections due to methicillin-resistant S aureus has been reported to be in decline in adults. Data for similar changes in pediatric populations are limited.

METHODS

Evaluation of S aureus susceptibility data for pediatric patients receiving care in the US Military Health System was performed. Microbiology and demographic data were collected for years 2005 through 2014. Trends in antibiotic susceptibility results were evaluated. Clinical and demographic characteristics were explored to assess for association with antibiotic susceptibilities.

RESULTS

In this study, 41 745 S aureus isolates from 39 207 pediatric patients were included. An overall increase in susceptibility of isolates to oxacillin was noted over this 10-year period; with over 60% of isolates oxacillin-susceptible in 2014. S aureus susceptibility to clindamycin declined over the study period; notably methicillin-susceptible S aureus susceptibility to clindamycin declined from 90% to 83% (P < .0001). Differences in oxacillin susceptibility between US regions decreased over time.

CONCLUSIONS

Similar to recent trends seen in adults, the proportion of pediatric S aureus infections secondary to methicillin-resistant S aureus appear to be decreasing, as is variability in US geographical resistance rates. Increasing clindamycin resistance among methicillin-susceptible S aureus should raise caution in the use of empirical clindamycin in presumed S aureus infection. Clinicians should be aware of regional susceptibility patterns when choosing empirical regimens.

Epidemiology of Surgical Site Infection in a Community Hospital Network

OBJECTIVE

To describe the epidemiology of complex surgical site infection (SSI) following commonly performed surgical procedures in community hospitals and to characterize trends of SSI prevalence rates over time for MRSA and other common pathogens

METHODS

We prospectively collected SSI data at 29 community hospitals in the southeastern United States from 2008 through 2012. We determined the overall prevalence rates of SSI for commonly performed procedures during this 5-year study period. For each year of the study, we then calculated prevalence rates of SSI stratified by causative organism. We created log-binomial regression models to analyze trends of SSI prevalence over time for all pathogens combined and specifically for MRSA.

RESULTS

A total of 3,988 complex SSIs occurred following 532,694 procedures (prevalence rate, 0.7 infections per 100 procedures). SSIs occurred most frequently after small bowel surgery, peripheral vascular bypass surgery, and colon surgery. Staphylococcus aureus was the most common pathogen. The prevalence rate of SSI decreased from 0.76 infections per 100 procedures in 2008 to 0.69 infections per 100 procedures in 2012 (prevalence rate ratio [PRR], 0.90; 95% confidence interval [CI], 0.82-1.00). A more substantial decrease in MRSA SSI (PRR, 0.69; 95% CI, 0.54-0.89) was largely responsible for this overall trend.

CONCLUSIONS

The prevalence of MRSA SSI decreased from 2008 to 2012 in our network of community hospitals. This decrease in MRSA SSI prevalence led to an overall decrease in SSI prevalence over the study period.

Determinants of Outcome in Hospitalized Patients With Methicillin-Resistant Staphylococcus aureus Bloodstream Infection: Results From National Surveillance in Canada, 2008-2012

BACKGROUND Bloodstream infection (BSI) due to methicillin-resistant Staphylococcus aureus (MRSA) is associated with considerable morbidity and mortality. OBJECTIVE To determine the incidence of MRSA BSI in Canadian hospitals and to identify variables associated with increased mortality. METHODS Prospective surveillance for MRSA BSI conducted in 53 Canadian hospitals from January 1, 2008, through December 31, 2012. Thirty-day all-cause mortality was determined, and logistic regression analysis was used to identify variables associated with mortality. RESULTS A total of 1,753 patients with MRSA BSI were identified (incidence, 0.45 per 1,000 admissions). The most common sites presumed to be the source of infection were skin/soft tissue (26.6%) and an intravascular catheter (22.0%). The most common spa types causing MRSA BSI were t002 (USA100/800; 55%) and t008 (USA300; 29%). Thirty-day all-cause mortality was 23.8%. Mortality was associated with increasing age (odds ratio, 1.03 per year [95% CI, 1.02-1.04]), the presence of pleuropulmonary infection (2.3 [1.4-3.7]), transfer to an intensive care unit (3.2 [2.1-5.0]), and failure to receive appropriate antimicrobial therapy within 24 hours of MRSA identification (3.2 [2.1-5.0]); a skin/soft-tissue source of BSI was associated with decreased mortality (0.5 [0.3-0.9]). MRSA genotype and reduced susceptibility to vancomycin were not associated with risk of death. CONCLUSIONS This study provides additional insight into the relative impact of various host and microbial factors associated with mortality in patients with MRSA BSI. The results emphasize the importance of ensuring timely receipt of appropriate antimicrobial agents to reduce the risk of an adverse outcome.

Bacteremia in Early Infancy: Etiology and Management

We reviewed the literature regarding bacteremia in early infancy (age ≤ 90 days). Bacteremia remains a major cause of morbidity and mortality in young infants. However, recent epidemiologic data suggest that the incidence of bacteremia is decreasing and the pathogens responsible for invasive disease are changing. These changes will impact the evaluation and management of young infants. We review the current epidemiology of community-acquired bacteremia in early infancy with particular emphasis on the causative agents, diagnostic evaluation, and empiric and definitive antimicrobial treatment.

In Vitro Activity of Ceftaroline against Staphylococcus aureus Isolates Collected in 2012 from Latin American Countries as Part of the AWARE Surveillance Program

The in vitro activities of ceftaroline and comparators, using broth microdilution, were determined against 1,066 Staphylococcus aureus isolates from hospitalized patients. Seventeen medical centers from Latin American countries contributed isolates. Methicillin-resistant S. aureus (MRSA) percentages ranged from 46% (Brazil) to 62% (Argentina). All methicillin-susceptible S. aureus (MSSA) isolates were susceptible to ceftaroline. Ceftaroline activity against MRSA varied with MIC90s of 0.5 (Venezuela) to 2 (Brazil, Chile, and Colombia) μg/ml, which was the highest MIC value. ST-5 was the most common sequence type.

A Randomized Clinical Trial of Single-Dose Versus Weekly Dalbavancin for Treatment of Acute Bacterial Skin and Skin Structure Infection

BACKGROUND

Acute bacterial skin and skin structure infections (ABSSSIs) are a cause of significant morbidity and therapy can be a burden to the healthcare system. New antibiotics that simplify treatment and avoid hospitalization are needed. This study compared the safety and efficacy of a single intravenous infusion of 1500 mg of dalbavancin to the 2-dose regimen.

METHODS

This study was a randomized, double-blind trial in patients aged >18 years with ABSSSIs. Patients were randomized to dalbavancin 1500 mg either as a single intravenous (IV) infusion or 1000 mg IV on day 1 followed 1 week later by 500 mg IV. The primary endpoint was a ≥20% reduction in the area of erythema at 48-72 hours in the intent-to-treat population. Noninferiority was to be declared if the lower limit of the 95% confidence interval (CI) on the difference in the outcomes was greater than -10%. Clinical outcome was also assessed at days 14 and 28.

RESULTS

Six hundred ninety-eight patients were randomized. Demographic characteristics were similar on each regimen, although there were more patients with methicillin-resistant Staphylococcus aureus (MRSA) at baseline on the 2-dose regimen (36/210 [17.1%] vs 61/220 [27.7%]). Dalbavancin delivered as a single dose was noninferior to a 2-dose regimen (81.4% vs 84.2%; difference, -2.9% [95% CI, -8.5% to 2.8%]). Clinical outcomes were also similar at day 14 (84.0% vs 84.8%), day 28 (84.5% vs 85.1%), and day 14 in clinically evaluable patients with MRSA in a baseline culture (92.9% vs 95.3%) in the single- and 2-dose regimens, respectively. Treatment-emergent adverse events occurred in 20.1% of the single-dose patients and 19.9% on the 2-dose regimen.

CONCLUSIONS

A single 1500-mg infusion of dalbavancin is noninferior to a 2-dose regimen, has a similar safety profile, and removes logistical constraints related to delivery of the second dose.

CLINICAL TRIALS REGISTRATION

NCT02127970.

Performance of BD Max StaphSR for Screening of Methicillin-Resistant Staphylococcus aureus Isolates among a Contemporary and Diverse Collection from 146 Institutions Located in Nine U.S. Census Regions: Prevalence of mecA Dropout Mutants

This study determined the performance of BD Max StaphSR and the rate of methicillin-resistant Staphylococcus aureus (MRSA) with an unrecognized staphylococcal cassette chromosome mec (SCCmec) right-extremity junction (MREJ) region among 907 methicillin-resistant S. aureus (MRSA) and 900 methicillin-susceptible S. aureus (MSSA) isolates. The rate of mecA/mecC dropout mutants was also evaluated. Only three MRSA isolates (99.7% sensitivity; 904/907) were classified as MSSA by the BD Max StaphSR assay, due to negative results for MREJ. Eight MSSA isolates (99.1% sensitivity; 892/900) were assigned as MRSA. However, six of these MSSA isolates had the mecA gene confirmed by PCR and sequencing (99.8% sensitivity; 898/900). Overall, 7.1% (64/900) of MSSA isolates showed results compatible with a mecA dropout genotype.

Nonimpact of Decolonization as an Adjunctive Measure to Contact Precautions for the Control of Methicillin-Resistant Staphylococcus aureus Transmission in Acute Care

This was an observational study comparing methicillin-resistant Staphylococcus aureus (MRSA) transmission with no decolonization of medical patients to required decolonization of all MRSA carriers during two consecutive periods: baseline with no decolonization of medical patients (16 months) and universal MRSA carrier decolonization (13 months). The setting was a one-hospital, 156-bed facility with 9,200 annual admissions. Regression models were used to compare rates of MRSA acquisition. The chi-square test was used to compare event frequencies. We used rates of MRSA clinical disease as an outcome monitor of the program. Analysis was done on 15,666 patients who had admission and discharge tests; 27.9% of inpatient days were occupied by a MRSA-positive patient (colonized patient-days) who received decolonization while hospitalized during the baseline period (this 27.9% represented those who had planned surgery) compared to 76.0% during the intervention period (P < 0.0001). The rate of MRSA transmission was 97 events (1.0%) for 9,415 admissions (2.0 transmission events/1,000 patient-days) during baseline and was 87 (1.4%) for 6,251 admissions (2.7 transmission events/1,000 patient-days) during intervention (P = 0.06; rate ratio, 0.74; 95% confidence interval [CI], 0.55 to 1.00). The MRSA nosocomial clinical disease rate was 5.9 infections/10,000 patient-days in the baseline period and was 7.2 infections/10,000 patient-days for the intervention period (rate ratio, 0.82; 95% CI, 0.46 to 1.45; P = 0.49). Decolonization of MRSA patients does not add benefit when contact precautions are used for patients colonized with MRSA in acute (hospital) care.

Evolving Epidemiology of Staphylococcus aureus Bacteremia

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) infections due to USA300 have become widespread in community and healthcare settings. It is unclear whether risk factors for bloodstream infections (BSIs) differ by strain type.

OBJECTIVE

To examine the epidemiology of S. aureus BSIs, including USA300 and non-USA300 MRSA strains.

DESIGN

Retrospective observational study with molecular analysis.

SETTING

Large urban public hospital.

PATIENTS

Individuals with S. aureus BSIs from January 1, 2007 through December 31, 2013.

METHODS

We used electronic surveillance data to identify cases of S. aureus BSI. Available MRSA isolates were analyzed by pulsed-field gel electrophoresis. Poisson regression was used to evaluate changes in BSI incidence over time. Risk factor data were collected by medical chart review and logistic regression was used for multivariate analysis of risk factors.

RESULTS

A total of 1,015 cases of S. aureus BSIs were identified during the study period; 36% were due to MRSA. The incidence of hospital-onset (HO) MRSA BSIs decreased while that of community-onset (CO) MRSA BSIs remained stable. The rate of CO- and HO- methicillin-susceptible S. aureus infections both decreased over time. More than half of HO-MRSA BSIs were due to the USA300 strain type and for 4 years, the proportion of HO-MRSA BSIs due to USA300 exceeded 60%. On multivariate analysis, current or former drug use was the only epidemiologic risk factor for CO- or HO-MRSA BSIs due to USA300 strains.

CONCLUSIONS

USA300 MRSA is endemic in communities and hospitals and certain populations (eg, those who use illicit drugs) may benefit from enhanced prevention efforts in the community.

Molecular and clinical characteristics of hospital and community onset methicillin-resistant Staphylococcus aureus strains associated with bloodstream infections

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSI) are classified epidemiologically as health care-associated hospital onset (HAHO)-, health care-associated community onset (HACO)-, or community-associated (CA)-MRSA. Clinical and molecular differences between HAHO- and HACO-MRSA BSI are not well known. Thus, we evaluated clinical and molecular characteristics of MRSA BSI to determine if distinct features are associated with HAHO- or HACO-MRSA strains. Molecular genotyping and medical record reviews were conducted on 282 MRSA BSI isolates from January 2007 to December 2009. MRSA classifications were 38% HAHO-, 54% HACO-, and 8% CA-MRSA. Comparing patients with HAHO-MRSA to those with HACO-MRSA, HAHO-MRSA patients had significantly higher rates of malignancy, surgery, recent invasive devices, and mortality and longer hospital stays. Patients with HACO-MRSA were more likely to have a history of renal failure, hemodialysis, residence in a long-term-care facility, long-term invasive devices, and higher rate of MRSA relapse. Distinct MRSA molecular strain differences also were seen between HAHO-MRSA (60% staphylococcal cassette chromosome mec type II [SCCmec II], 30% SCCmec III, and 9% SCCmec IV) and HACO-MRSA (47% SCCmec II, 35% SCCmec III, and 16% SCCmec IV) (P < 0.001). In summary, our study reveals significant clinical and molecular differences between patients with HAHO- and HACO-MRSA BSI. In order to decrease rates of MRSA infection, preventive efforts need to be directed toward patients in the community with health care-associated risk factors in addition to inpatient infection control.

Impact of prior healthcare-associated exposure on clinical and molecular characterization of methicillin-susceptible Staphylococcus aureus bacteremia: results from a retrospective cohort study

By virtue of medical advances and an aging society, people have increased opportunities for healthcare exposure. Little is known about the impact of healthcare exposure on the clinical features and molecular typing of methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia. We classified the onset of MSSA bacteremia into 3 mutually exclusive categories according to the Centers for Disease Control definition, and conducted a retrospective cohort study to investigate the differences among patients with community-associated (CA), healthcare-associated community onset (HACO), and hospital onset (HO) MSSA bacteremia at a medical center from January 1, 2002 through December 31, 2011. Antibiotic susceptibilities and multilocus sequence typing of MSSA isolates were also determined. A total of 290 patients with MSSA bacteremia, including of 165 (56.9%), 91 (31.4%), and 34 (11.7%) of HACO, HO, and CA, respectively, were studied. ST188 (29.3%) was the most common sequence type regardless of classification. Patients with HACO bacteremia were significantly older, had more solid tumors, higher Charlson scores, and more catheter-related bloodstream infections than those with CA bacteremia. The proportions of osteoarticular infections among patients with both HACO and CA bacteremia were higher than that of patients with HO bacteremia. By univariate analysis, patients with HO bacteremia had significantly higher in-hospital mortality compared to those with CA or HACO bacteremia (31.9% vs 18.8% and 20.4%). Multivariate analysis showed that Charlson score (odds ratio [OR], 1.29; 95% confidence interval [CI], 1.10-1.52), septic shock (OR, 5.28; 95% CI, 2.37-11.78), liver cirrhosis (OR, 3.57; 95% CI, 1.14-11.24), receipt of β-lactams other than oxacillin and cefazolin as definitive therapy (OR, 9.27; 95% CI, 4.25-20.23), and higher oxacillin minimum inhibitory concentration (MIC) (≥0.5 mg/L) (OR, 2.35; 95% CI, 1.05-5.25) of the causative pathogen were independently associated with in-hospital mortality. In conclusion, patients with HACO bacteremia had different host factors compared with those with CA bacteremia. Infection foci varied with different onset settings. Overall, ST188 was the most predominant sequence type. Onset settings were not independently associated with outcomes.

Extended-duration dosing and distribution of dalbavancin into bone and articular tissue

Dalbavancin is an intravenous lipoglycopeptide with activity against Gram-positive pathogens and an MIC90 for Staphylococcus aureus of 0.06 μg/ml. With a terminal half-life of >14 days, dosing regimens with infrequent parenteral administration become available to treat infectious diseases such as osteomyelitis and endocarditis that otherwise require daily dosing for many weeks. In order to support a rationale for these novel regimens, the pharmacokinetics over an extended dosing interval and the distribution of dalbavancin into bone and articular tissue were studied in two phase I trials and pharmacokinetic modeling was performed. Intravenous administration of 1,000 mg of dalbavancin on day 1 followed by 500 mg weekly for seven additional weeks was well tolerated and did not demonstrate evidence of drug accumulation. In a separate study, dalbavancin concentrations in cortical bone 12 h after infusion of a single 1,000-mg intravenous infusion were 6.3 μg/g and 2 weeks later were 4.1 μg/g. A two-dose, once-weekly regimen that would provide tissue exposure over the dalbavancin MIC for Staphylococcus aureus for 8 weeks, maximizing the initial exposure to treatment while minimizing the frequency of intravenous therapy, is proposed.

Preventing the introduction of meticillin-resistant Staphylococcus aureus into hospitals

The objective of this review was to provide an up-to-date account of the interventions used to prevent the introduction of meticillin-resistant Staphylococcus aureus (MRSA) from the expanding community and livestock reservoirs into hospitals in the USA, Denmark, The Netherlands and Western Australia. A review of existing literature and local guidelines for the management of MRSA in hospitals was performed. In Denmark, The Netherlands and Western Australia, where the prevalence of MRSA is relatively low, targeted admission screening and isolation of predefined high-risk populations have been used for several decades to successfully control MRSA in the hospital. Furthermore, in Denmark and The Netherlands, all identified MRSA carriers undergo routine decolonisation, whereas only carriers of particularly transmissible or virulent MRSA clones are subjected to decolonisation in Western Australia. In the USA, which continues to be a high-prevalence MRSA country, policies vary by state and even by hospital, and whilst guidelines from professional organisations provide a framework for infection control practices, these guidelines lack the authority of a legislative mandate. In conclusion, the changing epidemiology of MRSA, exemplified by the recent emergence of MRSA in the community and in food animals, makes it increasingly difficult to accurately identify specific high-risk groups to screen for MRSA carriage. Understanding the changing epidemiology of MRSA in a local as well as global context is fundamental to prevent the introduction of MRSA into hospitals.