Changing epidemiology of methicillin-resistant Staphylococcus aureus in the Veterans Affairs Healthcare System, 2002–2009

Impact of Community-Onset Methicillin-Resistant Staphylococcus aureus on Staphylococcus aureus Bacteremia in a Central Korea Veterans Health Service Hospital

BACKGROUND

No study has examined the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia in Korean veterans' hospitals. We investigated the microbiological and clinical epidemiology of S. aureus bacteremia at the central Veterans Health Services (VHS) hospital in Korea.

METHODS

Patients with S. aureus bacteremia were consecutively enrolled from February to August 2015. Bacteremia was classified as hospital-acquired (HA), community-onset healthcare-associated (COHA), or community-acquired (CA). MRSA bacteremia risk factors were analyzed. Species identification, antimicrobial susceptibility, and presence of luk and tst were tested. Staphylococcal cassette chromosome mec (SCCmec) typing, spa sequence typing agr polymorphism typing, and multilocus sequence typing were performed. Biofilm production and δ-hemolysin activity were measured to determine agr function.

RESULTS

In total, 60 patients were enrolled (30 HA, 23 COHA, and seven CA bacteremia); 44 (73.3%) had MRSA bacteremia (26 HA, 16 COHA, and two CA). MRSA bacteremia occurred more frequently in non-CA patients and those who had received antibiotic treatment within the past month (P<0.05). The major MRSA strains comprised 24 ST5-agr2-SCCmecII, 11 ST72-agr 1-SCCmecIV, and five ST8-agr1-SCCmecIV strains. Of 26 agr2-SCCmecII strains, including two MSSA strains, 25 were multidrug-resistant, 18 were tst-positive, and 13 were agr-defective, whereas only five of the 18 agr1-SCCmecIV strains were multidrug-resistant, and all were tst-negative and agr-intact. agr1-SCCmecIV and ST8-agr1-SCCmecIV strains were more likely than agr2-SCCmecII strains to be COHA.

CONCLUSIONS

MRSA was highly prevalent in both COHA and HA bacteremia. The introduction of virulent CA-MRSA strains may be an important cause of increased HA-MRSA bacteremia in VHS hospitals.

Background Information: Isolation Routines

The isolation of patients with suspected or documented infections—to not spread to others—has been discussed for hundreds of years. Guidelines are many, methods are different, attitudes show vide variations, routines and procedures are still changing, regulations by law may be absent, and some healthcare professionals may be afraid of adverse outcomes of isolation [1–44]. Microbes that are spread in the environment, on the hands and equipment are invisible. The invisible agent does not call on attention before the infection; clinical disease, hospital infection or nosocomial infection is a factum that can be registered [23, 28, 29, 35–37]. How to stop the transmission is often “to believe and not believe” in infection control.

Effect of Hand Antisepsis Agent Selection and Population Characteristics on Surgical Site Infection Pathogens

BACKGROUND

Selection of a pre-operative hand antisepsis agent has not been studied in relation to surgical site infection (SSI) culture data. In our hospital, we introduced an alcohol-based hand rub (ABR) in 2012 as an alternative to traditional aqueous surgical scrubs (TSS). It was the goal of this study to review any effect of this implementation on SSI pathogen characteristics. In addition, we sought to compare our SSI culture data with available National Healthcare Safety Network (NHSN) data. We hypothesized that SSI pathogens and resistant isolates are affected by surgical hand antisepsis technique.

METHODS

Data collected prospectively between 2007 and 2014 were retrospectively analyzed for two time periods at the Veterans Affairs Boston Healthcare System (VABHS): Before ABR implementation (TSS group) and after (ABR group). Pathogen distribution and pathogenic isolate resistance profiles were compared for TSS and ABR, and similar comparisons, along with procedure-associated SSI comparisons, were made between VABHS and NHSN. All VABHS data were interpreted and categorized according to NHSN definitions.

RESULTS

Compared with TSS (n = 4,051), ABR (n = 2,293) had a greater rate of Staphylococcus aureus (42.6% vs. 38.0%), Escherichia coli (12.8% vs. 9.9%), Pseudomonas aeruginosa (8.5% vs. 2.8%), and Enterobacter spp. (10.6% vs. 2.8%), and a lower rate of Klebsiella pneumoniae/K. oxytoca (4.3% vs. 8.5%) cultured from superficial and deep SSIs (p < 0.05). Of the S. aureus isolates, 35.0% and 44.4% were resistant to oxacillin/methicillin (MRSA) in ABR and TSS, respectively (p = 0.06). Looking at all SSIs, coagulase-negative staphylococci and K. pneumoniae/K. oxytoca at VABHS (4.0% and 10.4%, respectively) accounted for the biggest difference from NHSN (11.7% and 4.0%, respectively). Aside from MRSA, where there was no difference between VABHS and NHSN (42.9% vs. 43.7%, respectively; p = 0.87), statistically significant (p < 0.05) differences were observed among multi-drug-resistant K. pneumoniae/K. oxytoca (0% vs. 6.8%, respectively) and Escherichia coli (10.0% vs. 1.6%, respectively), as well as among extended-spectrum cephalosporin-resistant K. pneumoniae/K. oxytoca (4.8% vs. 13.2%, respectively) and Enterobacter (58.3% vs. 27.7%, respectively). VABHS had a greater proportion of SSIs in abdominal and vascular cases than did NHSN (48.6% vs. 22.5% and 13.2% vs. 1.5%, respectively). Overall, these differences were significant (p < 0.05).

CONCLUSIONS

The TSS and ABR groups differed in the distribution of pathogens recovered. Those differences, along with SSI pathogen distribution, pathogenic isolate resistance profiles, and procedure-associated SSIs between VABHS and NHSN, warrant further investigation.

Multiclonal methicillin-resistant Staphylococcus aureus (MRSA) outbreak and its control after use of the Veterans Affairs (VA) MRSA bundle in a VA long-term care facility, 2004-2014

A multiclonal methicillin-resistant Staphylococcus aureus (MRSA) outbreak with 91 infections occurred in our Veterans Affairs (VA) community living center over 46 months. Both similar and unique strains were shown by repetitive polymerase chain reaction to contribute to the outbreak, including 1 strain causing infections over a 33-month period. Most infections were soft tissue infections (67%). For 21 months after the initiation of the VA MRSA bundle, no infections were identified, and low rates of infection have been sustained an additional 4 years. The average annual rate of MRSA infection decreased by 62% (P < .001) from 0.6 per 1,000 resident days for 4 years prior to the bundle implementation to 0.09 per 1,000 resident days for 4 years after the bundle implementation.

Replacement of HA-MRSA by CA-MRSA infections at an academic medical center in the midwestern United States, 2004-5 to 2008

We noted anecdotally that infections designated as health care-associated (HA-) MRSA by epidemiologic criteria seemed to be decreasing in incidence at the University of Chicago Medical Center (UCMC) after 2004. We compared MRSA patients seen at any site of clinical care at UCMC and the isolates that caused their infections in 2004-5 (n = 545) with those in 2008 (n = 135). The percent of patients with MRSA infections cultured > 2 days after hospital admission decreased from 19.5% in 2004-5 to 7.4% in 2008 (p = 0.001). The percent in 2004-5 compared with 2008 who had a hospitalization (49.1% to 26.7%, p = 0.001) or surgery (43.0% to 14.1%, p<0.001) in the previous year decreased. In 2008 a greater percent of patients was seen in the emergency department (23.1% vs. 39.3%) and a smaller percent both in intensive care units (15.6% vs. 6.7%) and in other inpatient units (40.7% vs. 32.6%) (p<0.001). The percent of patients with CA-MRSA infections by the CDC epidemiologic criteria increased from 36.5% in 2004-5 to 62.2% in 2008 (p<0.001). The percent of MRSA isolates sharing genetic characteristics of USA100 decreased from 27.9% (152/545) to 12.6% (17/135), while the percent with CA-MRSA (USA300) characteristics increased from 53.2% (290/545) to 66.7% (90/135). The percent of infections that were invasive did not change significantly. Our data suggest that HA-MRSA infections, both by epidemiologic and microbiologic criteria, relative to CA-MRSA, decreased between 2004-5 and 2008 at UCMC.

Epidemiology of pneumococcal disease in a national cohort of older adults

Introduction

Streptococcus pneumoniae is a major cause of morbidity and mortality. We sought to describe the epidemiology of non-invasive and invasive pneumococcal disease in a national Veterans Affairs population within the United States.

Methods

We conducted a retrospective study in older patients (aged ≥50 years) with positive pneumococcal cultures from any site between 2002 and 2011. We described outpatient and inpatient pneumococcal disease incidence per 100,000 clinic visits/hospitalizations. Repeat cultures within a 30-day period were considered to represent the same episode. To describe the epidemiology of serious pneumococcal infections (bacteremia, meningitis, pneumonia), we assessed demographics, clinical characteristics, and risk factors for S. pneumoniae. Pneumonia was defined as a positive respiratory culture with a pneumonia diagnosis code. Bacteremia and meningitis were identified from positive cultures. Generalized linear mixed models were used to quantify changes over time.

Results

Over the study period, we identified 45,983 unique episodes of pneumococcal disease (defined by positive cultures). Incidence decreased significantly by 3.5% per year in outpatients and increased non-significantly by 0.2% per year in inpatients. In 2011, the outpatient and inpatient incidence was 2.6 and 328.1 infections per 100,000 clinic visits/hospitalizations, respectively. Among inpatients with serious infections, chronic disease risk factors for pneumococcal disease increased significantly each year, including respiratory disease (1.9% annually), diabetes (1.3%), and renal failure (1.0%). Overall, 30.2% of inpatients with serious infections had a pneumococcal immunization in the previous 5 years. Invasive disease (37.4% versus 34.9%, P = 0.004) and mortality (14.0% versus 12.7%, P = 0.045) were higher in non-vaccinated patients compared to vaccinated patients.

Conclusions

In our national study of older adults, the baseline health status of those with serious pneumococcal infections worsened over the study period. As the population ages and the chronic disease epidemic grows, the burden of pneumococcal disease is likely to increase thus highlighting the importance of pneumococcal vaccination.

Electronic supplementary material

The online version of this article (doi:10.1007/s40121-014-0025-y) contains supplementary material, which is available to authorized users.

Predictors of clinical success among a national Veterans Affairs cohort with methicillin-resistant Staphylococcus aureus pneumonia

BACKGROUND

The treatment of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia is exceedingly complicated, which is concerning because of the high mortality rate associated with the infection. Identification of independent predictors of clinical success can optimize patient care by assisting clinicians in treatment decisions.

OBJECTIVES

Our goal was to identify independent predictors of clinical success in a national Veterans Affairs (VA) cohort of patients with MRSA pneumonia.

METHODS

A nested case-control study was conducted among a cohort of VA patients with MRSA pneumonia receiving linezolid or vancomycin between January 2002 and September 2010. Cases included those demonstrating clinical success, defined as discharge from the hospital or intensive care unit by day 14 after treatment initiation, in the absence of death, therapy change, or intubation by day 14. Control subjects represented nonsuccess, defined as therapy change, intubation, intensive care unit admission, readmission, or death between treatment initiation and day 14. The potential predictors assessed included treatment, patient demographic and admission characteristics, previous health care and medication exposures, comorbidities, and medical history. Odds ratios (ORs) and 95% CIs were calculated from logistic regression.

RESULTS

Our study included 2442 cases of clinical success and 1290 control subjects. Demographic characteristics varied between the clinical success and nonsuccess groups, including age, race, and region of facility. A current diagnosis of chronic respiratory disease (46% vs 42%) and diagnosis of pneumonia in the year before the MRSA pneumonia admission (37% vs 32%) were both more common in the clinical success group. Despite these significant differences, only 2 predictors of clinical success were identified in our study: previous complication of an implant or graft, including mechanical complications and infections, in the year before the MRSA pneumonia admission (adjusted OR, 1.55 [95% CI, 1.17-2.06]) and treatment with linezolid (adjusted OR, 1.53 [95% CI, 1.12-2.10]). Predictors of nonsuccess (adjusted OR [95% CI) included diagnosis of concomitant urinary tract infection (0.82 [0.70-0.96]), intravenous line (0.76 [0.66-0.89]), previous coagulopathy (0.74 [0.56-0.96]), previous amputation procedure (0.72 [0.53-0.98]), current coagulopathy diagnosis (0.71 [0.53-0.96]), dialysis (0.54 [0.38-0.76]), multiple inpatient procedures (0.53 [0.45-0.62]), inpatient surgery (0.48 [0.41-0.57]), and previous endocarditis (0.24 [0.07-0.81]).

CONCLUSIONS

MRSA pneumonia tends to affect patients with complex care, and identification of the predictors of clinical success is useful when considering different therapeutic approaches. In this national cohort of VA patients with MRSA pneumonia, treatment was the only modifiable variable predicting clinical success.

Infection after primary total hip arthroplasty

The number of primary total hip arthroplasties (THAs) performed in the United States each year continues to climb, as does the incidence of infectious complications. The changing profile of antibiotic-resistant bacteria has made preventing and treating primary THA infections increasingly complex. The goal of this review was to summarize (1) the published data concerning the risk of surgical site infection (SSI) after primary THA by type of bacteria and (2) the effect of potentially modifying factors. The Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects, EMBASE, Web of Science, and PubMed were searched. Studies dated between 2001 and 2011 examining primary THA in adults were included. Meta-analysis of the collected data was performed. The pooled SSI rate was 2.5% (95% confidence interval [Cl], 1.4%-4.4%; P<.001; n=28,883). The pooled deep prosthetic joint infection (PJI) rate was 0.9% (95% Cl, 0.4%-2.2%; P<.001; n=28,883). The pooled rate of methicillin-resistant Staphylococcus aureus SSI was 0.5% (95% Cl, 0.2%-1.5%; P<.001; n=26,703). This is approximately 20% of all SSI cases. The pooled rate of intraoperative bacterial wound contamination was 16.9% (95% Cl, 6.6%-36.8%; P=.003; n=2180). All these results had significant heterogeneity. The postoperative risk of SSI was significantly associated with intraoperative bacterial surgical wound contamination (pooled rate ratio, 2.5; 95% Cl, 1.4%-4.6%; P=.001; n=19,049).

Comparative effectiveness of linezolid and vancomycin among a national veterans affairs cohort with methicillin-resistant Staphylococcus aureus pneumonia

STUDY OBJECTIVE

As variability in vancomycin dosing, susceptibility, and tolerability has driven the need to compare newer agents with vancomycin in real-world clinical settings, we sought to quantify the effectiveness of linezolid compared with vancomycin on clinical outcomes for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia.

DESIGN

Retrospective cohort study.

DATA SOURCE

Veterans Health Administration national databases.

PATIENTS

Adults admitted to Veterans Affairs hospitals between January 2002 and September 2010 with diagnosis codes for MRSA and pneumonia, plus initiation and receipt of at least 3 days of continuous intravenous vancomycin therapy (4943 patients) or intravenous or oral linezolid therapy (328 patients) while in the hospital.

MEASUREMENTS AND MAIN RESULTS

Propensity score-adjusted Cox proportional hazards regression models quantified the effect of linezolid compared with vancomycin on time to 30-day mortality (primary outcome), therapy change, hospital discharge, discharge from intensive care, intubation, 30-day readmission, and 30-day MRSA reinfection. In addition, a composite outcome of clinical success was defined as discharge from the hospital or intensive care unit by day 14 after treatment initiation, in the absence of death, therapy change, or intubation by day 14. Subgroup analyses were performed in a validated microbiology-confirmed MRSA subgroup and clinical subgroup meeting clinical criteria for infection. Although a number of baseline variables differed significantly between the vancomycin and linezolid treatment groups, balance was achieved within propensity score quintiles. A significantly lower rate of therapy change was observed in the linezolid group (adjusted hazard ratio [HR] 0.68, 95% confidence interval [CI] 0.48-0.96). The clinical success rate was significantly higher among patients treated with linezolid (adjusted HR 1.25, 95% CI 1.07-1.47). Comparable findings were observed in the subgroup analyses.

CONCLUSION

Individual clinical outcomes were similar among patients treated for MRSA pneumonia with linezolid compared with vancomycin. A significantly higher rate of the composite outcome of clinical success was observed, however, among patients treated with linezolid compared with vancomycin.

Relationships between the importation, transmission, and nosocomial infections of methicillin-resistant Staphylococcus aureus: an observational study of 112 Veterans Affairs Medical Centers

BACKGROUND

The study of hospital methicillin-resistant Staphylococcus aureus (MRSA) epidemiology is complicated by its transmissibility. Our objective was to understand how MRSA importation and transmission influence MRSA nosocomial infections in Veterans Affairs Medical Centers (VAMCs).

METHODS

We performed hospital-level analyses of acute-care MRSA admission prevalence, acquisition rates, and incident nosocomial clinical culture (INCC) rates, each a surrogate measure of importation, transmission, and nosocomial infection, respectively. We studied 112 VAMCs from October 2007 through September 2010, after the start of a bundled intervention including active surveillance for MRSA. We analyzed data using generalized linear mixed models.

RESULTS

A total of 2.9 million surveillance tests were collected from 1.4 million patient admissions. Overall MRSA admission prevalence was 11.4%, acquisition was 5.2 per 1000 patient-days at risk, and INCC was 1.8 per 1000 patient-days at risk. A 10% increase in a hospital's average admission prevalence was associated with a 9.7% increase in its weekly acquisition rates (P < .001) and a 9.8% increase in its weekly INCC rates (P < .001). Significant decreases were observed in all 3 measures during the study period (P < .001). When INCC rates were stratified by nasal MRSA carriage at admission, a significant downward trend was observed only among those initially negative.

CONCLUSIONS

Measured associations between MRSA admission prevalence, acquisition rate, and INCC rate were consistent with the hypothesis that decreased acquisition led to decreased importation, which in turn further abated acquisition. The downward trend in INCC rate specifically among individuals with negative admission surveillance tests suggests that decreasing transmission contributed to lower rates of nosocomial MRSA infection.

Patient-days used for isolation in a community hospital

BACKGROUND

Isolation of patients with known or suspected infection strains the resources of hospitals, but little information exists on the actual utilization of isolation beds.

METHODS

The infection control team of a community hospital keeps a log of hospital days used for isolation. We obtained information from this log for August 2009 through August 2010 on hospital days for isolation due to methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, Clostridium difficile, other multidrug-resistant organisms, and disorders necessitating droplet or airborne isolation, such as tuberculosis, meningococcal meningitis, varicella, and influenza. We also included days of isolation used to rule out the presence of these infections. All data from the medical-surgical and intensive care units were included unless the start date or end date of isolation was missing. Utilization percentages (isolation days divided by total hospital days) were calculated for the total period, for each month, and for each category of isolation.

RESULTS

During the study period, 18.1% of hospital days were devoted to isolation (13.7% for definite infection and 4.4% to rule out infection). Monthly utilization ranged from 13.4% to 22%. Patients with confirmed methicillin-resistant S aureus or C difficile infections and patients with possible C difficile infection accounted for 75% of the isolation days.

CONCLUSIONS

Isolation beds were required for a substantial portion of total patient-days in our study. Our data may help hospitals use hospital beds efficiently and predict nursing needs, hospital supply needs, and workload for environmental services.

Impact of preoperative MRSA screening and decolonization on hospital-acquired MRSA burden

BACKGROUND

Hospital-acquired infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are a source of morbidity and mortality. S. aureus is the most common pathogen in prosthetic joint infections and the incidence of MRSA is increasing.

QUESTIONS/PURPOSES

The purposes of this study were (1) to determine the MRSA prevalence density rate at a specialty orthopaedic hospital before and after the implementation of a screening and decolonization protocol,(2) to compare our prevalence density to that of an affiliated university hospital, to control for changes in MRSA prevalence density that might have been independent of the decolonization protocol, and (3) to measure the admission prevalence density rate of MRSA in an elective orthopaedic surgery population and the compliance rate of 26 patients with the protocol [corrected].

METHODS

In October 2008, we implemented a MRSA screening and decolonization protocol for patients undergoing elective orthopaedic surgery. Nasal swabs were used for screening and mupirocin nasal ointment and chlorhexidine skin antisepsis where prescribed for decolonization to all patients. At the surgical visit, compliance was measured and the patients who were MRSA positive received vancomycin for antibiotic prophylaxis. Institution wide surveillance for multidrug-resistant organisms, including MRSA provided a comparison of the change in MRSA burden at the orthopaedic hospital versus the university hospital.

RESULTS

Before implementation of the preoperative staphylococcal decolonization protocol there were 79 MRSA-positive cultures in 64,327 patient-days for a prevalence density rate of 1.23 per 1000 patient-days. After protocol implementation, 53 MRSA-positive cultures were identified in 63,860 patient-days for a rate of 0.83 per 1000 patient-days. Before the protocol, the MRSA prevalence density at the specialty hospital was similar to that of the university hospital; after implementation of the protocol, the prevalence density at the specialty hospital was 33% lower than that of the university hospital. The MRSA admission prevalence was 3.02%. The compliance rate was greater than 95%.

CONCLUSIONS

Implementation of a staphylococcal decolonization protocol at a single specialty orthopaedic hospital decreased the prevalence density of MRSA.

MRSA nasal colonization burden and risk of MRSA infection

BACKGROUND

Staphylococcus aureus nasal colonization burden has been identified as a risk factor for infection. This study evaluates methicillin-resistant S aureus (MRSA) nasal burden, as defined by the cycle threshold (Ct) and risk of subsequent infection.

METHODS

In a retrospective cohort study, United States veterans were classified into 3 MRSA nasal colonization groups: noncarriers, low burden (Ct > 24 cycles), and high burden (Ct ≤ 24 cycles). MRSA infections were identified prospectively, and clinical information was obtained by chart review. Multivariate logistic regression assessed the association of MRSA nasal burden and risk of MRSA infection.

RESULTS

During 4-years of follow-up, 4.3% of noncarriers, 18.5% of low burden, and 17.2% of high burden developed a MRSA infection. In multivariate analysis, MRSA nasal colonization was a risk factor for MRSA infection (P = .008) with low burden (risk ratio [RR], 3.62; 95% confidence interval [CI]: 1.47-8.93) and high burden (RR, 2.71; 95% CI: 0.95-7.72) associated with subsequent MRSA infection when compared with noncarriers. When compared with low burden, high burden nasal carriers were not at increased risk of infection (RR, 0.75; 95% CI 0.36-1.55).

CONCLUSION

MRSA nasal colonization was a risk factor for MRSA infection. High nasal burden of MRSA did not increase the risk of infection.

A population-based study of the epidemiology and clinical features of methicillin-resistant Staphylococcus aureus infection in Pennsylvania, 2001-2010

No U.S. general population-based study has characterized the epidemiology and risk factors, including skin and soft tissue infection (SSTI), for healthcare-associated (HA) and community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA). We estimated the incidence of HA- and CA-MRSA and SSTI over a 9-year period using electronic health record data from the Geisinger Clinic in Pennsylvania. MRSA cases were frequency-matched to SSTI cases and controls in a nested case-control analysis. Logistic regression was used to assess risk factors, while accounting for antibiotic administration. We identified 1713 incident CA- and 1506 HA-MRSA cases and 78 216 SSTI cases. On average, from 2005 to 2009, the annual incidence of CA-MRSA increased by 34%, HA-MRSA by 7%, and SSTI by 4%. Age, season, community socioeconomic deprivation, obesity, smoking, previous SSTI, and antibiotic administration were identified as independent risk factors for CA-MRSA.

Reduction of methicillin-resistant Staphylococcus aureus infection among veterans in Atlanta

OBJECTIVE

Describe local changes in the incidence of community-onset and hospital-onset methicillin-resistant Staphylococcus aureus (MRSA) infection and evaluate the impact of MRSA active surveillance on hospital-onset infection.

DESIGN

Observational study using prospectively collected data.

SETTING

Atlanta Veterans Affairs Medical Center (AVAMC).

PATIENTS

All patients seen at the AVAMC over an 8-year period with clinically and microbiologically proven MRSA infection.

METHODS

All clinical cultures positive for MRSA were prospectively identified, and corresponding clinical data were reviewed. MRSA infections were classified into standard clinical and epidemiologic categories. The Veterans Health Administration implemented the MRSA directive in October 2007, which required active surveillance cultures in acute care settings.

RESULTS

The incidence of community-onset MRSA infection peaked in 2007 at 5.45 MRSA infections per 1,000 veterans and decreased to 3.14 infections per 1,000 veterans in 2011 ([Formula: see text] for trend). Clinical and epidemiologic categories of MRSA infections did not change throughout the study period. The prevalence of nasal MRSA colonization among veterans admitted to AVAMC decreased from 15.8% in 2007 to 11.2% in 2011 ([Formula: see text] for trend). The rate of intensive care unit (ICU)-related hospital-onset MRSA infection decreased from October 2005 through March 2007, before the MRSA directive. Rates of ICU-related hospital-onset MRSA infection remained stable after the implementation of active surveillance cultures. No change was observed in rates of non-ICU-related hospital-onset MRSA infection.

CONCLUSIONS

Our study of the AVAMC population over an 8-year period shows a consistent trend of reduction in the incidence of MRSA infection in both the community and healthcare settings. The etiology of this reduction is most likely multifactorial.

Impact of strain typing methods on assessment of relationship between paired nares and wound isolates of methicillin-resistant Staphylococcus aureus

The anterior nares are the site of choice for the Veterans Administration methicillin-resistant Staphylococcus aureus (MRSA) surveillance program; however, a correlation between nares colonization and concomitant wound infections has not been well established. The purpose of this study was 3-fold: to determine the relatedness of MRSA isolates from 40 paired wound and nares specimens by four different strain typing methods, to determine concordance of typing methods, and to establish a baseline of MRSA types at this medical center. Isolates were typed by repetitive PCR (rep-PCR) (DiversiLab System; DL) and SpectraCell Raman analysis (SCRA) (commercially available methods that can be performed within a clinical lab), pulsed-field gel electrophoresis (PFGE), and an antibiotic susceptibility profile (AB). Whole-genome optical mapping (WGM) (OpGen, Inc.) was performed on selected isolates. All methods agreed that 26 pairs were indistinguishable and four pairs were different. Discrepant results were as follows: 4 where only SCRA was discordant, 3 where only AB was discordant, 2 where both DL and AB were discordant, and 1 where both DL and SCRA were discordant. All WGM agreed with PFGE. After discrepancy resolution, 80% of the pairs were indistinguishable and 20% were different. A total of 56% of nares results were nonpredictive if negative nares and positive wound cultures are included. Methods agreed 85 to 93% of the time; however, congruence of isolates to a clade was lower. Baseline analysis of types showed that 15 pairs were unique to single patients (30 strains, 38%; 47% of the matching pairs). Twenty-five strains (30%) represented a single clade identical by PFGE, SCRA, and DL, decreasing specificity. Typing method and institutional type frequency are important in assessing MRSA strain relatedness.