Retrospective study of prevalence of Community Associated Methicillin Resistant Staphylococcus Aureus (CA-MRSA) seen in Texas MedClinics, San Antonio, TX from April 2006-August 2009

Purpose. To evaluate the presence of Community Associated–Methicillin Resistant Staphylococcus Aureus, CA-MRSA, in abscesses and skin and soft tissue infections presenting at 9 urgent care clinics in San Antonio, TX. ^ Methods. During the 40-month retrospective study (April 2006 to August 2009), wound cultures collected in 9 urgent care centers were evaluated for MRSA growth, antibiotics prescribed, follow up wound care, and antibiotic prescribing habits by physicians for all patients presenting with abscesses and skin/soft tissue infections. ^ Results. Across 9 urgent care centers in San Antonio, TX, 36,797 abscesses and cases of skin and soft tissue infections were treated during 40 months. Of the 36,797 cases, 9290 patients had wound cultures sent with 5,630 cultures sent to Texas MedClinic’s primary lab. Of the 5630 cultures sent to their primary lab, this reflected a prevalence of 4727 (84 %) cultures were positive for MRSA. Of the 9290 patients who had a wound culture sent (April 10th, 2006 to August 31st, 2009), a total of 4,307 antibiotics were prescribed. The top five antibiotics prescribed for CA-MRSA were Bactrim (55.5%), Clindamycin (18.4%), Bactroban (5%), Amoxicillin (3.5%), and Doxycycline (3%) representing 85.4% of the antibiotics prescribed. 8809/9290 (94.8%) of patients required no more than 3 follow up visits. Of the 33 physicians working full time during the entire study period, 29/33 (87.8%) of the physicians were family medicine physicians and represented varied prescribing rates of antibiotics between 11-76% with 26/33 (78.8%) of physicians prescribing antibiotics greater than 40% of the time.^ Conclusions. Abscesses and soft tissue infections are a common presenting complaint to urgent care centers. This study reveals that antibiotic-prescribing practices can be improved with physician education since this high prevalence was not known previously. Also, treating abscesses with limited packing has been shown to be a viable option in this particular circumstance and would be open field for additional clinical research. Due to the high prevalence of CA-MRSA skin and soft tissue infections among patients presenting to urgent care centers presumptive treatment for MRSA is indicated. Increasing levels of resistance to penicillin antibiotics is concerning and warrants alternative antibiotic management strategies.^

Assessing pediatric nasal carriage of S. aureus & MRSA

Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) has become an increasing problem in the community. Nasal carriage of these bacteria has been shown to be a predisposing factor for infection and environmental contamination. This serious public health concern prompted an investigation to assess the pediatric nasal carriage of these bacteria in an effort to better understand the populations at risk and prevention of infection.^ This prospective study surveys 30 children from the Northwest Assistance Ministries (NAM) pediatric clinic from October 2008 to the present. Two nasal swabs were taken in 2-4 week intervals to determine S. aureus carrier status. Microbiologic tests were conducted to isolate and identify S. aureus from nasal cultures. Children with 2 cultures positive for S. aureus were classified as persistent carriers, those with 1 positive and 1 negative culture were classified as intermittent carriers, and those with 2 negative cultures were classified as noncarriers. This information was related to patient records and statistical analyses (X 2 and t-tests) were performed.^ Distribution of S. aureus carriage related to patient demographics (age, sex, & race) was showed no significant differences between S. aureus positive and S. aureus negative patient populations (p = 0.8). Additionally, the distribution of carrier status related to demographics also showed no significant difference (p = 0.8). Finally, the distribution of carrier status related to relevant medical history (immunizations current, past infection, & antibiotic use at time of swabbing) showed no significant difference (p = 0.4).^ This study is a snapshot of an ongoing study to assess the pediatric nasal carriage of S. aureus and MRSA. The inability to draw any reliable conclusion from the distribution of data is likely a result of an inadequate samples size. This is one of few studies assessing pediatric nasal carriage of S. aureus and targeting an underrepresented, Hispanic population is especially unique. Continuing this study allows for a better understanding of the epidemiology of this bacterium which will hopefully lead to appropriate interventions thus preventing future S. aureus infections.^

Prevalence of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization among dental professionals

Background. MRSA (methicillin-resistant Staphylococcus aureus) is a multi-drug resistant bacterium that is quite prevalent in social environments where close person-to-person contact and crowding are an issue. In dental settings, the likelihood of transmission of MRSA may be higher than among other healthcare practitioners because of the close proximity between a patient's nose (where MRSA colonizes) and the field of procedure (the mouth) to the dental professional. Objective. To estimate the prevalence of MRSA nasal colonization among dental professionals (dentists and dental hygienists) in the Greater Houston Metropolitan Area, Texas, and analyze its associations with demographic, professional and personal protective equipment-related variables. Methods. 800 dental professionals (400 dentists and 400 dental hygienists) were randomly selected in the Greater Houston Metropolitan Area. Multiple waves of nasal swab kits and a self-administered questionnaire were mailed to increase the response rate of the study population. The swabs were cultured on chromagenic agar growth medium and bacterial growth results were evaluated after 18 hours. Positively selected bacterial colonies were confirmed as MRSA by further culturing these isolated bacteria on blood agar plates. Associations between positive nasal swabs and self-reported professional practice patterns, personal protective equipment use and demographics were analyzed using multiple logistic regression. Main Results. Completed questionnaires and nasal swabs were received from 496 study participants (68%). Fourteen cultures were positive for MRSA (4.2% among dentists and 1.6% among dental hygienists, p=0.07). After adjusting for gender, dental hygienists had a significantly lower prevalence of nasal colonization of MRSA as compared to dentists (OR: 0.20, 95% CI: 0.05–0.75). No other significant associations or interactions were found. Conclusion. The prevalence of nasal colonization with MRSA among dentists is similar to that reported for health care workers in general, whereas prevalence among dental hygienists is only slightly above that of the general population (1%). Differences in practice patterns and use of personal protective equipment did not explain this difference in this study, and was possibly due either to residual confounding or unexplored risk factors. Increased prevalence of MRSA among dentists warrants further investigation as to the reason for the increased rate and to allow implementation of measures to avoid transmission and progression to disease. ^

Retrospective analysis of Methicillin-Resistant Staphylococcus Aureus (MRSA) skin and Soft-Tissue Infections (SSTI) in a university hospital emergency department (ED)

Study Objective: Identify the most frequent risk factors of Community Acquired-MRSA (CA-MRSA) Skin and Soft-tissue Infections (SSTIs) using a case series of patients and characterize them by age, race/ethnicity, gender, abscess location, druguse and intravenous drug-user (IVDU), underlying medical conditions, homelessness, treatment resistance, sepsis, those whose last healthcare visit was within the last 12 months, and describe the susceptibility pattern from this central Texas population that have come into the University Medical Center Brackenridge (UMCB) Emergency Department (ED). ^ Methods: This study was a retrospective case-series medical record review involving a convenience sample of patients in 2007 from an urban public hospital's ED in Texas that had a SSTI that tested positive for MRSA. All positive MRSA cultures underwent susceptibility testing to determine antibiotic resistance. The demographic and clinical variables that were independently associated with MRSA were determined by univariate and multivariate analysis using logistic regression to calculate odds ratios (OR), 95% confidence intervals, and significance (p≤ 0.05). ^ Results: In 2007, there were 857 positive MRSA cultures. The demographics were: males 60% and females 40%, with the average age of 36.2 (std. dev. =13) the study population consisted of non-Hispanic white (42%), Hispanics (38%), and non-Hispanic black (18.8%). Possible risk factors addressed included using recreational drugs (not including IVDU) (27%) homelessness (13%), diabetes status (12.6%) or having an infectious disease, and IVDU (10%). The most frequent abscess location was the leg (26.6%), followed by the arm and torso (both 13.7%). Eighty-three percent of patients had one prominent susceptibility pattern that had a susceptibility rate for the following antibiotics: trimethoprim/sulfamethoxazole (TMP-SMX) and vancomycin had 100%, gentamicin 99%, clindamycin 96%, tetracycline 96%, and erythromycin 56%. ^ Conclusion: The ED is becoming an important area for disease transmission between the sterile hospital environment and the outside environment. As always, it is important to further research in the ED in an effort to better understand MRSA transmission and antibiotic resistance, as well as to keep surveillance for the introduction of new opportunistic pathogens into the population. ^

Cost-effectiveness of intensified interventions to control healthcare-associated MRSA infections -- A systematic literature review

Methicillin Resistant Staphylococcus aureus healthcare-associated infections (MRSA HAIs) are a major cause of morbidity in hospitalized patients. They pose great economic burden to hospitals caring for these patients. Intensified Interventions aim to control MRSA HAIs. Cost-effectiveness of Intensified Interventions is largely unclear. We performed a review of cost-effectiveness literature on Intensified Interventions , and provide a summary of study findings, the status of economic research in the area, and information that will help decision-makers at regional level and guide future research.^ We conducted literature search using electronic database PubMed, EBSCO, and The Cochrane Library. We limited our search to English articles published after 1999. We reviewed a total of 1,356 titles, and after applying our inclusion and exclusion criteria selected seven articles for our final review. We modified the Economic Evaluation Abstraction Form provided by CDC, and used this form to abstract data from studies.^ Of the seven selected articles two were cohort studies and the remaining five were modeling studies. They were done in various countries, in different study settings, and with different variations of the Intensified Intervention . Overall, six of the seven studies reported that Intensified Interventions were dominant or at least cost-effective in their study setting. This effect persisted on sensitivity testing.^ We identified many gaps in research in this field. The cost-effectiveness research in the field is mostly composed of modeling studies. The studies do not always clearly describe the intervention. The intervention and infection costs and the sources for these costs are not always explicit or are missing. In modeling studies, there is uncertainty associated with some key model inputs, but these inputs are not always identified. The models utilized in the modeling studies are not always tested for internal consistency or validity. Studies usually test the short term cost-effectiveness of Intensified Interventions but not the long results.^ Our study limitation was the inability to adjust for differences in study settings, intervention costs, disease costs, or effectiveness measures. Our study strength is the presentation of a focused literature review of Intensified Interventions in hospital settings. Through this study we provide information that will help decision makers at regional level, help guide future research, and might change clinical care and policies. ^

Host-pathogen interactions of secreted and surface Staphylococcus aureus factors

Staphylococcus aureus is an opportunistic bacterial pathogen that can infect humans and other species. It utilizes an arsenal of virulence factors to cause disease, including secreted and cell wall anchored factors. Secreted toxins attack host cells, and pore-forming toxins destroy target cells by causing cell lysis. S. aureus uses cell-surface adhesins to attach to host molecules thereby facilitating host colonization. The Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs) are a family of cell-wall anchored proteins that target molecules like fibronectin and fibrinogen. The Serine-aspartate repeat (Sdr) proteins are a subset of staphylococcal MSCRAMMs that share similar domain organization. Interestingly, the amino-terminus, is composed of three immunoglobulin-folded subdomains (N1, N2, and N3) that contain ligand-binding activity. Clumping factors A and B (ClfA and ClfB) and SdrG are Sdr proteins that bind to fibrinogen (Fg), a large, plasma glycoprotein that is activated during the clotting cascade to form fibrin. In addition to recognizing fibrinogen, ClfA and ClfB can bind to other host ligands. Analysis of S. aureus strains that cause osteomyelitis led to the discovery of the bone-sialoprotein-binding protein (Bbp), an Sdr protein. Because several MSCRAMMs target more than one molecule, I hypothesized that Bbp may recognize other host proteins. A ligand screen revealed that the recombinant construct BbpN2N3 specifically recognizes human Fg. Surface plasmon resonance was used to determine the affinity of BbpN2N3 for Fg, and a dissociation constant of 540 nM was determined. Binding experiments performed with recombinant Fg chains were used to map the binding of BbpN2N3 to the Fg Aalpha chain. Additionally, Bbp expressed on the surface of Lactococcus lactis and S. aureus Newman bald mediated attachment of these bacteria to Fg Aalpha. To further characterize the interaction between the two proteins, isothermal titration calorimetry and inhibition assays were conducted with synthetic Fg Aalpha peptides. To determine the physiological implications of Bbp binding to Fg, the effect of Bbp on fibrinogen clotting was studied. Results show that Bbp binding to Fg inhibits the formation of fibrin. The consequences of this interaction are currently under investigation. Together, these data demonstrate that human Fg is a novel ligand for Bbp. This study indicates that the MSCRAMM Bbp may aid in staphylococcal attachment by targeting both an extracellular matrix and a blood plasma protein. The implications of these novel findings are discussed.

Dissemination of methicillin-resistant Staphylococcus aureus USA300 sequence type 8 lineage in Latin America.

BACKGROUND: Methicillin-resistant Staphylococus aureus (MRSA) is an important nosocomial and community-associated (CA) pathogen. Recently, a variant of the MRSA USA300 clone emerged and disseminated in South America, causing important clinical problems. METHODS: S. aureus isolates were prospectively collected (2006-2008) from 32 tertiary hospitals in Colombia, Ecuador, Peru, and Venezuela. MRSA isolates were subjected to antimicrobial susceptibility testing and pulsed-field gel electrophoresis and were categorized as health care-associated (HA)-like or CA-like clones on the basis of genotypic characteristics and detection of genes encoding Panton-Valentine leukocidin and staphylococcal cassette chromosome (SCC) mec IV. In addition, multilocus sequence typing of representative isolates of each major CA-MRSA pulsotype was performed, and the presence of USA300-associated toxins and the arcA gene was investigated for all isolates categorized as CA-MRSA. RESULTS: A total of 1570 S. aureus were included; 651 were MRSA (41%)--with the highest rate of MRSA isolation in Peru (62%) and the lowest in Venezuela (26%)--and 71%, 27%, and 2% were classified as HA-like, CA-like, and non-CA/HA-like clones, respectively. Only 9 MRSA isolates were confirmed to have reduced susceptibility to glycopeptides (glycopeptide-intermediate S. aureus phenotype). The most common pulsotype (designated ComA) among the CA-like MRSA strains was found in 96% of isolates, with the majority (81%) having a < or =6-band difference with the USA300-0114 strain. Representative isolates of this clone were sequence type 8; however, unlike the USA300-0114 strain, they harbored a different SCCmec IV subtype and lacked arcA (an indicator of the arginine catabolic mobile element). CONCLUSION: A variant CA-MRSA USA300 clone has become established in South America and, in some countries, is endemic in hospital settings.

Clinical and microbiological aspects of linezolid resistance mediated by the cfr gene encoding a 23S rRNA methyltransferase.

The cfr (chloramphenicol-florfenicol resistance) gene encodes a 23S rRNA methyltransferase that confers resistance to linezolid. Detection of linezolid resistance was evaluated in the first cfr-carrying human hospital isolate of linezolid and methicillin-resistant Staphylococcus aureus (designated MRSA CM-05) by dilution and diffusion methods (including Etest). The presence of cfr was investigated in isolates of staphylococci colonizing the patient's household contacts and clinical isolates recovered from patients in the same unit where MRSA CM-05 was isolated. Additionally, 68 chloramphenicol-resistant Colombian MRSA isolates recovered from hospitals between 2001 and 2004 were screened for the presence of the cfr gene. In addition to erm(B), the erm(A) gene was also detected in CM-05. The isolate belonged to sequence type 5 and carried staphylococcal chromosomal cassette mec type I. We were unable to detect the cfr gene in any of the human staphylococci screened (either clinical or colonizing isolates). Agar and broth dilution methods detected linezolid resistance in CM-05. However, the Etest and disk diffusion methods failed to detect resistance after 24 h of incubation. Oxazolidinone resistance mediated by the cfr gene is rare, and acquisition by a human isolate appears to be a recent event in Colombia. The detection of cfr-mediated linezolid resistance might be compromised by the use of the disk diffusion or Etest method.

Prevalence and risk factors of methicillin-resistant Staphylococcus aureus in critically-ill hospitalized patients in a tertiary care center in Houston, Texas: An active surveillance pilot project

Objective. The objective of this study is to determine the prevalence of MRSA colonization in adult patients admitted to intensive care units at an urban tertiary care hospital in Houston, Texas and to evaluate the risk factors associated with colonization during a three month active-screening pilot project. Design. This study used secondary data from a small cross-sectional pilot project. Methods. All patients admitted to the seven specialty ICUs were screened for MRSA by nasal culture. Results were obtained utilizing the BD GeneOhm™ IDI-MRSA assay in vitro diagnostic test, for rapid MRSA detection. Statistical analysis was performed using the STATA 10, Epi Info, and JavaStat. Results . 1283/1531 (83.4%) adult ICU admissions were screened for nasal MRSA colonization. Of those screened, demographic and risk factor data was available for 1260/1283 (98.2%). Unresolved results were obtained for 73 patients. Therefore, a total of 1187/1531 (77.5%) of all ICU admissions during the three month study period are described in this analysis. Risk factors associated with colonization included the following: hospitalization within the last six months (odds ratio 2.48 [95% CI, 1.70-3.63], p=0.000), hospitalization within the last 12 months, (odds ratio 2.27 [95% CI, 1.57-3.80], p=0.000), and having diabetes mellitus (odds ratio 1.63 [95% CI, 1.14-2.32], p=0.007). Conclusion. Based on the literature, the prevalence of MRSA for this population is typical of other prevalence studies conducted in the United States and coincides with the continual increasing trend of MRSA colonization. Significant risk factors were similar to those found in previous studies. Overall, the active surveillance screening pilot project has provided valuable information on a population not widely addressed. These findings can aid in future interventions for the education, control, prevention, and treatment of MRSA. ^

Characterization of Staphylococcus aureus isolates associated with pediatric carriage in Houston, Texas

Infections caused by Methicillin-resistant Staphylococcus aureus (MRSA) have been of great concern in hospitals due the difficulty in treating virulent, antibiotic resistant microorganisms in sensitive populations including children, the elderly, and immunocomprimised individuals. Since the late 1990's, MRSA infections have become a problem in the general community, and the strains of S. aureus that cause infections in the community are known to be genetically different than the hospital acquired strains. Community-acquired strains tend to be more virulent, affecting even relatively healthy individuals, and disease presentation tends to be more diverse than diseases observed in patients suffering from hospital-acquired strains. From the year 2000 to the present, there has been a significant increase in community-acquired infections in children, a population already particularly sensitive to S. aureus infection. Genotyping the strains of CA-MRSA circulating in the pediatric population is an important step in developing better antibiotic treatment strategies. Additionally, determining the carriage status of individuals in this population and comparing these data with strain genotypes will also be valuable in establishing prevention and control practices. ^

Impact of real time polymerase chain reaction technology on the therapeutic approach to treatment of staphylococcal infections

Can the early identification of the species of staphylococcus responsible for infection by the use of Real Time PCR technology influence the approach to the treatment of these infections? ^ This study was a retrospective cohort study in which two groups of patients were compared. The first group, ‘Physician Aware’ consisted of patients in whom physicians were informed of specific staphylococcal species and antibiotic sensitivity (using RT-PCR) at the time of notification of the gram stain. The second group, ‘Physician Unaware’ consisted of patients in whom treating physicians received the same information 24–72 hours later as a result of blood culture and antibiotic sensitivity determination. ^ The approach to treatment was compared between ‘Physician Aware’ and ‘Physician Unaware’ groups for three different microbiological diagnoses—namely MRSA, MSSA and no-SA (or coagulase negative Staphylococcus). ^ For a diagnosis of MRSA, the mean time interval to the initiation of Vancomycin therapy was 1.08 hours in the ‘Physician Aware’ group as compared to 5.84 hours in the ‘Physician Unaware’ group (p=0.34). ^ For a diagnosis of MSSA, the mean time interval to the initiation of specific anti-MSSA therapy with Nafcillin was 5.18 hours in the ‘Physician Aware’ group as compared to 49.8 hours in the ‘Physician Unaware’ group (p=0.007). Also, for the same diagnosis, the mean duration of empiric therapy in the ‘Physician Aware’ group was 19.68 hours as compared to 80.75 hours in the ‘Physician Unaware’ group (p=0.003) ^ For a diagnosis of no-SA or coagulase negative staphylococcus, the mean duration of empiric therapy was 35.65 hours in the ‘Physician Aware’ group as compared to 44.38 hours in the ‘Physician Unaware’ group (p=0.07). However, when treatment was considered a categorical variable and after exclusion of all cases where anti-MRS therapy was used for unrelated conditions, only 20 of 72 cases in the ‘Physician Aware’ group received treatment as compared to 48 of 106 cases in the ‘Physician Unaware’ group. ^ Conclusions. Earlier diagnosis of MRSA may not alter final treatment outcomes. However, earlier identification may lead to the earlier institution of measures to limit the spread of infection. The early diagnosis of MSSA infection, does lead to treatment with specific antibiotic therapy at an earlier stage of treatment. Also, the duration of empiric therapy is greatly reduced by early diagnosis. The early diagnosis of coagulase negative staphylococcal infection leads to a lower rate of unnecessary treatment for these infections as they are commonly considered contaminants. ^

Effect of the emergence of community acquired methicillin resistant Staphylococcus aureus on microbial resistance patterns seen during a seven year study of minocycline/rifampin catheter use

Background. Health care associated catheter related blood stream infections (CRBSI) represent a significant public health concern in the United States. Several studies have suggested that precautions such as maximum sterile barrier and use of antimicrobial catheters are efficacious at reducing CRBSI, but there is concern within the medical community that the prolonged use of antimicrobial catheters may be associated with increased bacterial resistance. Clinical studies have been done showing no association and a significant decrease in microbial resistance with prolonged minocycline/rifampin (M/R) catheter use. One explanation is the emergence of community acquired methicillin resistant Staphylococcus aureus (MRSA), which is more susceptible to antibiotics, as a cause of CRBSI.^ Methods. Data from 323 MRSA isolates cultured from cancer patients at The University of Texas MD Anderson Cancer center from 1997-2007 displaying MRSA infection were analyzed to determine whether there is a relationship between resistance to minocycline and rifampin and prolonged wide spread use of minocycline (M/R) catheters. Analysis was also conducted to determine whether there was a significant change in the prevalence community acquired MRSA (CA-MRSA) during this time period and if this emergence act as a confounder masquerading the true relationship between microbial resistance and prolonged M/R catheter use.^ Results. Our study showed that the significant (p=0.008) change in strain type over time is a confounding variable; the adjusted model showed a significant protective effect (OR 0.000281, 95% CI 1.4x10 -4-5.5x10-4) in the relationship between MRSA resistance to minocycline and prolonged M/R catheter use. The relationship between resistance to rifampin and prolonged M/R catheter use was not significant.^ Conclusion. The emergence of CA-MRSA is a confounder and in the relationship between resistance to minocycline and rifampin and prolonged M/R catheter use. However, despite the adjustment for the more susceptible CA-MRSA the widespread use of M/R catheters does not promote microbial resistance. ^

MLST analysis of Staphylococcus aureus isolates identified in a pediatric cohort in northwest Houston

The purpose of this research was to identify S. aureus isolates among a pediatric outpatient population served by the Northwest Assistance Ministries clinic as a means of identifying unique clones using multi-locus sequence typing (MLST). DNA was extracted from previously collected isolates and seven housekeeping genes were amplified and sequenced. It was hypothesized that due to the unique demographics of the population studied, there would be a high diversity of clones identified and unique strains would exist in the population. Current literature and results from this study found this to be true. 9 strains were identified in a sample of 20 patients and 5 were unique strains. Three of 4 pairs of siblings enrolled in the study were colonized with the same strain, and all cultures known to be MRSA were novel sequence strain F. These types of genetic analyses can help identify mechanisms associated with strain colonization and spread throughout respective communities. ^

Implementation of active surveillance cultures and associated infection control practices for the reduction of methicillin resistant Staphylococcus aureus in the healthcare setting: An interrupted time series analysis

OBJECTIVE. To determine the effectiveness of active surveillance cultures and associated infection control practices on the incidence of methicillin resistant Staphylococcus aureus (MRSA) in the acute care setting. DESIGN. A historical analysis of existing clinical data utilizing an interrupted time series design. ^ SETTING AND PARTICIPANTS. Patients admitted to a 260-bed tertiary care facility in Houston, TX between January 2005 through December 2010. ^ INTERVENTION. Infection control practices, including enhanced barrier precautions, compulsive hand hygiene, disinfection and environmental cleaning, and executive ownership and education, were simultaneously introduced during a 5-month intervention implementation period culminating with the implementation of active surveillance screening. Beginning June 2007, all high risk patients were cultured for MRSA nasal carriage within 48 hours of admission. Segmented Poisson regression was used to test the significance of the difference in incidence of healthcare-associated MRSA during the 29-month pre-intervention period compared to the 43-month post-intervention period. ^ RESULTS. A total of 9,957 of 11,095 high-risk patients (89.7%) were screened for MRSA carriage during the intervention period. Active surveillance cultures identified 1,330 MRSA-positive patients (13.4%) contributing to an admission prevalence of 17.5% in high-risk patients. The mean rate of healthcare-associated MRSA infection and colonization decreased from 1.1 per 1,000 patient-days in the pre-intervention period to 0.36 per 1,000 patient-days in the post-intervention period (P<0.001). The effect of the intervention in association with the percentage of S. aureus isolates susceptible to oxicillin were shown to be statistically significantly associated with the incidence of MRSA infection and colonization (IRR = 0.50, 95% CI = 0.31-0.80 and IRR = 0.004, 95% CI = 0.00003-0.40, respectively). ^ CONCLUSIONS. It can be concluded that aggressively targeting patients at high risk for colonization of MRSA with active surveillance cultures and associated infection control practices as part of a multifaceted, hospital-wide intervention is effective in reducing the incidence of healthcare-associated MRSA.^