Risk factors for colonization with methicillin-resistant Staphylococcus aureus (MRSA) in patients admitted to an urban hospital: emergence of community-associated MRSA nasal carriage

Prevalence of Staphylococcus aureus nasal colonization in emergency department personnel

STUDY OBJECTIVE

Nasal colonization with Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) can precede infection in patients and contacts. Although general population S aureus/MRSA rates are well described, the prevalence of S aureus and MRSA nasal colonization in emergency department health care workers is not defined. We seek to determine the prevalence of S aureus and MRSA nasal colonization among ED health care workers without evidence of an active site of staphylococcal infection and identify variables associated with colonization.

METHODS

We prospectively studied a convenience sample of ED health care workers from 5 urban teaching hospitals in Pittsburgh, PA. Each participant completed a questionnaire and nasal culturing. We tested susceptibility with the oxacillin disc diffusion method. We analyzed data with descriptive statistics and univariate regression, with alpha set at 0.05.

RESULTS

Of 255 subjects, 23% were physicians; 62% were nurses, nursing assistants, or patient care technicians; and 15% were clerical staff or social service workers. Of 81 (31.8%) S aureus isolates, 11 (13.6%) were MRSA, an overall prevalence of 4.3%. All positive MRSA samples were from nurses, nursing assistants, or patient care technicians. No other covariate had an association with S aureus or MRSA colonization.

CONCLUSION

In this urban ED health care worker population, the prevalence of S aureus is similar but MRSA nasal colonization is higher than previously reported estimates in the general population of the United States. Physicians and nonpatient contact ED health care workers did not have MRSA colonization.

A model for surveillance of methicillin-resistant Staphylococcus aureus

It is well recognized that methicillin-resistant Staphylococcus aureus (MRSA) has become a community pathogen. Several key differences between community-associated and hospital-associated MRSA strains exist, including distinct methicillin resistance genes and genetic backgrounds and differing susceptibility to antibiotics. Recent studies have demonstrated that typical hospital and community strains easily move between hospital and community environments. Despite evidence of MRSA's expanding reach in the community, the best methods for population-level detection and containment have not been established. In an effort to determine effective methods for monitoring the spread of MRSA, we reviewed the literature on hospital-associated and community-associated MRSA (CA-MRSA) in the community and proposed a model for enhanced surveillance. By linking epidemiologic and molecular techniques within a surveillance system that coordinates activities in the community and health-care setting, scientists and public health officials can begin to measure the true extent of CA-MRSA in communities and hospitals.

Antimicrobial-resistant pathogens: an emerging pediatric threat

The clinical impact of these three bacterial threats is readily apparent to any who practice pediatrics. The potential virulence of CA-MRSA and MDR pneumococci and the threat of failed antimicrobial options for MDRGN pose enormous challenges now and in the near future. With careful attention to antimicrobial stewardship, however, and knowledge of the clinical and epidemiologic factors of these organisms, one can hope to mitigate the impact on patient care and outcomes while awaiting ongoing discovery of new antimicrobial options. Most important, however, will be careful and thoughtful management of any new antimicrobial products to protect their efficacy for the future.

Using marker pens on patients: a potential source of cross infection with MRSA

INTRODUCTION

Marker pens are widely used in surgery but pre-operative marking of patients may be a cause of bacterial cross-infection.

PATIENTS AND METHODS

Two experiments were performed to assess whether marking pens can be cause of cross-infection: (i) 26 indelible marker pens were collected from surgical wards for analysis; and (ii) 'fresh' as well as 'dry' (artificially dried by removing cap and exposing tip for 2 h) new permanent marker pens, and whiteboard marker pens were inoculated by dipping the tips into various concentrations of methicillin-resistant Staphylococcus aureus (MRSA). Each pen was inoculated onto 2 blood agar plates at 0 (immediately after inoculation) to 30 min at various intervals, 4 h and 24 h. The plates were incubated for 18 h at 35 degrees C in an incubator.

RESULTS

Of 26 pens collected from the wards, 2 cultured Micrococci spp. (skin commensals). The constituents of new 'fresh' pen tips rapidly kill MRSA - in all cases by 4 h, but usually within minutes. At high inoculum concentrations, MRSA is not killed immediately. Dry marker pens harbour MRSA for at least 30 min and probably longer.

CONCLUSIONS

Marker pens can act as fomites for nosocomial infection. The ethanol-based ink in permanent marker pens has a bactericidal action against MRSA that starts within seconds, and they are likely to be safe to use with a gap of at least 2 min between patients. Usually, harmless skin commensals are not pathogenic except in immunocompromised patients. Old or dried-out marker pens can harbour pathogens and should be discarded before attempted use on patients. We recommend disposable markers for the immunocompromised and patients with a known positive MRSA status.

Antimicrobial resistance prevention initiative--an update: proceedings of an expert panel on resistance

Antimicrobial resistance is a growing problem that complicates the treatment of important nosocomial and community-acquired infections. It is a worldwide problem that spans the range of human pathogens, including bacteria, fungi, and viruses. This update from the Antimicrobial Resistance Prevention Initiative (ARPI) provides a review of some important trends in antibiotic, antifungal, and antiviral resistance. Areas of focus include multidrug-resistant bacteria in the hospital setting; the growing problem of community-acquired methicillin-resistant Staphylococcus aureus; triazole and polyene resistance in nosocomial infections caused by non-Candida albicans or Aspergillus species, and the utility of in vitro susceptibility testing for these fungal infections; antiviral resistance in alpha- or beta-herpesviruses causing genital herpes or cytomegalovirus infection in immunocompromised hosts; and concerns about a possible pandemic involving avian influenza A and the importance of minimizing emergence of resistant strains of this highly pathogenic virus. The challenges in each area are different, but the general keys to addressing the growing problem of antimicrobial resistance continue to be responsible antimicrobial stewardship and the development of newer antimicrobial agents.

Risk factors associated with methicillin-resistant Staphylococcus aureus infection in patients admitted to the ED

OBJECTIVES

The objective of our study was to define the characteristics of patients admitted to the emergency department (ED) presenting with a methicillin-resistant Staphylococcus aureus (MRSA) infection.

PATIENTS AND METHODS

The study included all patients admitted to the ED between January 2003 and December 2004 in whom a staphylococcal infection was documented. The risk factors associated with carriage of MRSA, the diagnosis made in the ED, and the treatment administered were established from the patients' medical files. The sites from which the bacteria were isolated, the spectrum of resistance of the staphylococci to different antibiotics, and the presence or absence of the gene coding for Panton-Valentin leukocidin for certain S aureus isolates were determined from the reports issued by the bacteriologic department. Two groups of patients were compared: those with an infection caused by MRSA and those with an infection due to methicillin-susceptible S aureus (MSSA).

RESULTS

A total of 238 patients were included, 93 presenting with an infection caused by MRSA and 145 an infection due to MSSA. The patients harboring MRSA had a higher median age than those carrying MSSA (74 vs 61 years, P = .0001), experienced a greater loss of autonomy (according to the Knauss index), and had more comorbidity factors. Nine patients, younger than 40 years, presented with an infection due to MRSA in the absence of any comorbidity factor or any factor associated with carriage of these bacteria. Seven patients in the MRSA group were tested for Panton-Valentine leukocidin genes, and a positive result was obtained in 2 of them. Regardless of whether the infection was caused by MRSA or by MSSA, the bacteria were most frequently isolated from a cutaneous site, in 40% and 65% of the patients, respectively. Irrespective of the group, 28% of the patients presented with bacteremia. The spectrum of resistance of these MRSA strains suggested a hospital rather than community origin. The initial antibiotic therapy was rarely appropriate in the case of an infection due to MRSA.

CONCLUSION

Infections caused by MRSA accounted for a high proportion of the staphylococcal infections diagnosed in the ED, necessitating a rational approach to the prescription of antibiotics for infections of this type.

Prevalence of and risk factors for methicillin-resistant Staphylococcus aureus carriage at hospital admission

To determine the prevalence of and risk factors for methicillin-resistant Staphylococcus aureus (MRSA) carriage at the time of admission to our hospital, we screened the medical records of 1,128 patients for demographic and clinical data. The antimicrobial resistance pattern and genotype of MRSA isolates were studied. The prevalence of MRSA carriage at hospital admission was 1.4%. Older patients and patients previously admitted to healthcare centers were the most likely to have MRSA carriage at admission.

Practical management: community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA): the latest sports epidemic

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has gained international recognition as a superbug that causes serious infectious outbreaks in high-risk populations such as athletes. Clusters of cases in various athletic teams, particularly contact sports, have been reported since 1993 in the United States and more recently in Canada. CA-MRSA infections are not limited to North America, and all athletes are considered high risk. Skin-to-skin contact appears to be the primary mode of transmission. While typical infections are local skin and soft-tissue abscesses, CA-MRSA infections can spread systemically and lead to significant morbidity and mortality if not promptly identified and treated. The gold standard of treatment for all abscesses is incision and drainage with wound culture for bacterial identification and antibiotic sensitivity testing. A limited number of antibiotics are currently useful in the treatment of CA-MRSA and are reviewed. Geographical variation in patterns of antibiotic resistance further complicates the treatment. Meticulous, consistent use of infection prevention strategies is critical to control outbreaks in the athletic population. Good hygiene, prompt identification of infection, limited exposure to infected persons and contaminated objects, and proper treatment combined with close follow-up of infected athletes will help contain CA-MRSA outbreaks. Future research is needed to explore person-to-person and fomite transmission risks, to define the significance of nasal carriage and skin colonization in relation to CA-MRSA infections, and to further investigate antibiotic resistance patterns. Universal education is needed for all athletes and personnel who provide care in the athletic setting to help control this widespread epidemic.

Effect of laparotomy on clearance and cytokine induction in Staphylococcus aureus infected lungs

RATIONALE

Staphylococcus aureus is a major pathogen complicating postsurgical care.

OBJECTIVES

To test the effect of sterile laparotomy (LAP) on pulmonary clearance of S. aureus in a murine model.

METHODS

Control and LAP mice were infected intranasally with 10(8) cfu of S. aureus. Microbial clearance, pulmonary leukocyte recruitment, and cytokine profiles were compared between the groups. Antibody neutralization or cytokine gene knockout mice were used to evaluate the role of cytokines.

MEASUREMENTS AND MAIN RESULTS

Laparotomy resulted in a 10-fold increase in S. aureus lung colony-forming units on Days 2 and 3 postinfection. Both groups cleared the infection by Day 4. No defect in leukocyte recruitment into the lungs was observed in infected LAP animals; however, an increase in the number of Mac-3-positive cells and a significant decrease of cells with high surface expression of Fc-gammaR suggest suboptimal activation of leukocytes in the lungs of infected LAP animals. Infected LAP mice had decreased expression of interferon (IFN)-gamma and increased expression of mRNA for IL-13 in the lungs on Day 1 postinfection and decreased levels of IL-6, keratinocyte-derived chemokine (KC), and macrophage inflammatory protein-2 (MIP-2) in bronchoalveolar lavage at Day 2 postinfection. Neutralization of IFN-gamma mimicked the effect of LAP with impaired clearance on Day 2.

CONCLUSIONS

Sterile LAP induced temporary deactivation of innate immune responses to pulmonary S. aureus challenge. Impaired microbial clearance was accompanied by altered cytokine expression and suboptimal activation of pulmonary leukocytes. Lack of early IFN-gamma induction in the infected lungs of LAP animals is a likely mechanism contributing to the observed phenotype.

Community-associated methicillin-resistant Staphylococcus aureus prevalence: how common is it? A methodological comparison of prevalence ascertainment

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are becoming increasingly prevalent. There is geographic variation in their reported prevalence across the United States; however, studies reporting on CA-MRSA prevalence also demonstrate great variability in their case-finding methodology. We conducted a study to see how three different methods to ascertain CA-MRSA prevalence would lead to different estimates.

METHODS

Different methods were used to identify cases of CA-MRSA colonization and/or infection in New York City. Method 1: retrospective review of clinical and surveillance cultures identified through a hospital computer database. Method 2: prospective collection of surveillance cultures in the same hospital's emergency department. Method 3: prospective collection of surveillance cultures in a community setting.

RESULTS

Differing values for CA-MRSA prevalence resulted depending on the method and denominator used. All nares cultures as the denominator led to prevalence estimates of 0.3%-0.6%; all S. aureus as the denominator led to rates of 1.2%-5%; all MRSA as the denominator led to estimates of 5.5%-50%.

CONCLUSIONS

A comparison of three methods revealed that variability in case-finding methodologies can lead to different prevalence estimates. Key factors to consider when comparing CA-MRSA rates include the definition of CA-MRSA, choice of denominator, and method and setting of sample collection.

Antimicrobial resistance prevention initiative--an update: proceedings of an expert panel on resistance

Antimicrobial resistance is a growing problem that complicates the treatment of important nosocomial and community-acquired infections. It is a worldwide problem that spans the range of human pathogens, including bacteria, fungi, and viruses. This update from the Antimicrobial Resistance Prevention Initiative (ARPI) provides a review of some important trends in antibiotic, antifungal, and antiviral resistance. Areas of focus include multidrug-resistant bacteria in the hospital setting; the growing problem of community-acquired methicillin-resistant Staphylococcus aureus; triazole and polyene resistance in nosocomial infections caused by non-Candida albicans or Aspergillus species, and the utility of in vitro susceptibility testing for these fungal infections; antiviral resistance in alpha- or beta-herpesviruses causing genital herpes or cytomegalovirus infection in immunocompromised hosts; and concerns about a possible pandemic involving avian influenza A and the importance of minimizing emergence of resistant strains of this highly pathogenic virus. The challenges in each area are different, but the general keys to addressing the growing problem of antimicrobial resistance continue to be responsible antimicrobial stewardship and the development of newer antimicrobial agents.

Role of previous hospitalization in clinically-significant MRSA infection among HIV-infected inpatients: results of a case-control study

Background

HIV-infected subjects have high incidence rates of Staphylococcus aureus infections, with both methicillin-susceptible and methicillin-resistant (MRSA) strains. Possible explanations could include the high burden of colonization, the behavioral risk factors, and the frequent exposures to health care facilities of HIV-infected patients. The purpose of the study was to assess the risk factors for clinically- significant methicillin-resistant Staphylococcus aureus (CS-MRSA) infections in HIV-infected patients admitted to Infectious Diseases Units.

Methods

From January 1, 2002 to December 31, 2005, we conducted a retrospective case-control (1:2) study. We identified all the cases of CS-MRSA infections in HIV-infected patients admitted to the National Institute for Infectious Diseases (INMI) "Lazzaro Spallanzani" in the 4-year study period. A conditional logistic regression model was used to identify risk factors for CS-MRSA infection.

Results

We found 27 CS-MRSA infections, i.e. 0.9 CS-MRSA infections per 100 HIV-infected individuals cared for in our Institute. At multivariate analysis, independent predictors of CS-MRSA infection were cumulative hospital stay, invasive procedures in the previous year, and low CD4 cell count. Particularly, the risk for CS-MRSA increased by 14% per an increase of 5 days hospitalization in the previous year. Finally, we identified a low frequency of community-acquired MRSA infections (only 1 of 27; 3.7%) among HIV-infected patients.

Conclusion

Clinicians should be aware of the risk for CS-MRSA infection in the clinical management of HIV-infected patients, especially in those patients with a low CD4 cell count, longer previous hospital stay, and previous invasive procedures.

Infective endocarditis caused by USA300 methicillin-resistant Staphylococcus aureus (MRSA)

We report seven cases of infective endocarditis caused by USA300 methicillin-resistant Staphylococcus aureus (MRSA) at an urban, tertiary care, academic institution. Five strains were community associated and two were healthcare associated. All patients were injection drug users. Staphylococcus aureus isolates were characterised as USA300-type MRSA using pulsed-field gel electrophoresis. Five cases were right-sided endocarditis and two cases were left-sided. The mean length of in-hospital antimicrobial therapy was 23 days and the mean length of total antibiotic therapy was 55 days. Complications included heart failure resulting in valve replacement in one patient as well as death in that patient. As USA300 strains of MRSA continue to increase in prevalence, clinicians must be aware of the increasing spectrum of illness in considering management and prevention strategies.

Legislative mandates for use of active surveillance cultures to screen for methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci: Position statement from the Joint SHEA and APIC Task Force

Legislation aimed at controlling antimicrobial-resistant pathogens through the use of active surveillance cultures to screen hospitalized patients has been introduced in at least 2 US states. In response to the proposed legislation, the Society for Healthcare Epidemiology of America (SHEA) and the Association for Professionals in Infection Control and Epidemiology, Inc., (APIC) have developed this joint position statement. Both organizations are dedicated to combating health care-associated infections with a wide array of methods, including the use of active surveillance cultures in appropriate circumstances. This position statement reviews the proposed legislation and the rationale for use of active surveillance cultures, examines the scientific evidence supporting the use of this strategy, and discusses a number of unresolved issues surrounding legislation mandating use of active surveillance cultures. The following 5 consensus points are offered. (1) Although reducing the burden of antimicrobial-resistant pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE), is of preeminent importance, the APIC and the SHEA do not support legislation to mandate use of active surveillance cultures to screen for MRSA, VRE, or other antimicrobial-resistant pathogens. (2) The SHEA and the APIC support the continued development, validation, and application of efficacious and cost-effective strategies for the prevention of infections caused by MRSA, VRE, and other antimicrobial-resistant and antimicrobial-susceptible pathogens. (3) The APIC and the SHEA welcome efforts by health care consumers, together with private, local, state, and federal policy makers, to focus attention on and formulate solutions for the growing problem of antimicrobial resistance and health care-associated infections. (4) The SHEA and the APIC support ongoing additional research to determine and optimize the appropriateness, utility, feasibility, and cost-effectiveness of using active surveillance cultures to screen both lower-risk and high-risk populations. (5) The APIC and the SHEA support stronger collaboration between state and local public health authorities and institutional infection prevention and control experts.

Utilizing Pharmacy Records to Assess Antibiotic Prescribing Patterns on the Incidence of Community-Acquired Methicillin-Resistant Staphylococcus aureus Infections in Children

OBJECTIVE To assess the effect of prior antibiotic therapy on the incidence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections in children.

METHODS This was a concurrent and retrospective review of antibiotic records for children < 18 years of age with documented CA-MRSA infection identified between January 1, 2004, and December 31, 2005. Antibiotic records were compared against a control group. The primary outcome was the incidence of CA-MRSA using linear regression as a function of age and prior antibiotic therapy (i.e., 3 months prior to admission). Secondary objectives included a comparison of antibiotic courses and classes and a description of antibiotic susceptibilities in patients with CA-MRSA

RESULTS Data from 26 patients were included. Nine out of 51 patients (18%) with CA-MRSA were included. Another 17 children were enrolled in the control group. The median age was approximately 1.75 years (0.08–14 years) in the CA-MRSA group versus 2.75 years (0.005-15 years) in the control group. A statistical difference was noted in the number of patients with prior antibiotic exposure between the CA-MRSA and control group, 8 (88.9%) versus 6 (35.3%), respectively (P = .01). Antibiotic exposure was found to be a significant independent risk factor (P = .005; 95% CI, 0.167–0.846) for the development of CA-MRSA. The interaction between antibiotic exposure and age < 3 was the most significant predictor of CA-MRSA (P = .019; 95% CI, 0.139–1.40).

CONCLUSIONS Prior antibiotic therapy in patients < 3 years of age was associated with a significant risk of developing CA-MRSA. A comprehensive assessment of CA-MRSA patients should include objective methods of measuring prior antibiotic exposure such as pharmacy records.

Management of Community-Associated Methicillin-ResistantStaphylococcus aureusInfections in Children

In recent years, community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as a pathogen in children without established risk factors, and its prevalence in the United States is increasing. Although many CA-MRSA infections are mild, primarily involving the skin and soft tissues, the organism can cause serious, invasive, and life-threatening infections. To provide a comprehensive review of the epidemiology, clinical features, therapy, and prevention of CA-MRSA infections in children, we performed MEDLINE (1966-January 2006) and Cochrane Library searches, and reviewed abstracts for relevance to S. aureus infections. Only articles pertaining to CA-MRSA infections in pediatrics were closely examined. As a genetically distinct pathogen, CA-MRSA is generally susceptible to multiple non-beta-lactam antimicrobials. The optimal treatment for CA-MRSA infections in pediatric patients has not been well studied. Common antibiotics used include clindamycin, trimethoprim-sulfamethoxazole, vancomycin, and rifampin. Rational empiric antimicrobial therapy for infections caused by S. aureus requires consideration of the possibility of methicillin resistance. The local prevalence and susceptibilities of CA-MRSA, severity of infection, and individual risk factors should be considered in selecting treatment.

Rapid multiplex PCR assay for identification of USA300 community-associated methicillin-resistant Staphylococcus aureus isolates

Recent reports have noted a discernible increase in the number of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections in patients without traditional risk factors. In the United States, the most prominent CA-MRSA strain encodes Panton-Valentine leukocidin (PVL) cytotoxin genes, belongs to pulsed field gel electrophoresis type USA300 and multilocus sequence type 8, and carries staphylococcal cassette chromosome mec (SCCmec) type IV. At present, molecular characterization of MRSA strains, such as USA300, can be time-consuming and is often beyond the technical capability of many clinical laboratories, making routine identification difficult. We analyzed the chromosomal regions flanking the SCCmec element in 44 USA300 MRSA isolates and identified a signature "AT repeat" sequence within the conserved hypothetical gene SACOL0058 located 1.4 kb downstream of the 3' end of the J1-SCCmec chromosomal junction. Only USA300 isolates tested contained a sequence of > or =6 AT repeats in combination with PVL (e.g., related USA500 or Iberian strains had > or =6 AT repeats but were PVL negative). Using a locked nucleic acid primer specific for > or =6 AT repeats in combination with primers to detect PVL, we developed a multiplex PCR assay specific for the identification of USA300 strains. Multiplex results were 100% concordant with DNA sequencing, suggesting that the method has promise as a means of rapidly identifying USA300 isolates.

Significant pathogens isolated from surgical site infections at a community hospital in the Midwest

BACKGROUND

Studies examining the incidence of microorganisms isolated from surgical site infections (SSIs) have been conducted primarily at large academic health care centers. Results from these studies have revealed that methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a significant pathogen in SSIs. Minimal data are available from smaller, community hospitals on the incidence of microorganisms associated with SSIs, particularly the incidence of MRSA in SSIs.

METHODS

A retrospective study was performed to identify the microorganisms associated with SSIs in patients who underwent class I and II surgeries at a small urban to rural community hospital from January 2003 through December 2004.

RESULTS

A total of 10,672 surgeries was performed, and 89 SSIs were identified. Staphylococcus aureus was the most common pathogen (25.8%). Enterobacteriaceae were the second most frequently isolated organisms (12.4%), followed by streptococci species (11.2%), coagulase-negative staphylococci (10.1%), enterococci species (7.9%), and Pseudomonas aeruginosa (6.7%). MRSA was isolated from 4.5% of the SSIs.

CONCLUSION

We have demonstrated that the spectrum of microorganisms isolated in SSIs at a community hospital is comparable with that reported in studies conducted at large academic health care centers, including the emergence of MRSA as a pathogen in SSIs. This information will guide future infection control initiatives to reduce SSIs.

Ophthalmic Manifestations of Infections Caused by the USA300 Clone of Community-Associated Methicillin-Resistant Staphylococcus aureus

PURPOSE

To report the microbiological, clinical, and pathological characteristics of community-associated methicillin-resistant Staphylococcus aureus (CAMRSA) infections of the eye and orbit.

DESIGN

Prospective case series.

PARTICIPANTS

Nine patients with CAMRSA infections of the eye and orbit were identified during a 6-month period at 2 tertiary care hospitals in San Francisco.

METHODS

Case identification was by prospective case selection and retrospective laboratory review of 549 MRSA cultures collected in the 2 hospitals. Ophthalmic microbial isolates were analyzed by pulsed-field gel electrophoresis and compared with a control CAMRSA clone (USA300). Clinical characteristics of patients infected with CAMRSA were reviewed, and all surgical specimens underwent pathological examination.

MAIN OUTCOME MEASURES

Pulsed-field gel electrophoresis banding patterns of MRSA isolates, antibiotic sensitivity profiles, patient demographics, systemic and ocular complications of infection, and posttreatment visual acuities.

RESULTS

Nine ophthalmic isolates were CAMRSA clone USA300. The infections included orbital cellulitis, endogenous endophthalmitis, panophthalmitis, lid abscesses, and septic venous thrombosis. Patients were treated with trimethoprim-sulfamethoxazole, rifampin, clindamycin, or vancomycin based on microbial sensitivity studies and severity of infection. Eight of the 9 patients had no history of hospitalization. Seven patients required hospitalization, 3 required surgery, and an additional 4 required invasive procedures. Eight patients had good visual outcomes, but 1 deteriorated to no light perception. Pathological analyses showed extensive necrosis in eyelid and orbital specimens, and disorganized atrophy bulbi in an enucleated eye.

CONCLUSION

The USA300 CAMRSA clone, which carries Panton-Valentine leukocidin genes, can cause aggressive infections of the eye and orbit in hospital-naive patients. Treatment of infections often required debridement of necrotic tissues in addition to non-beta-lactam class antibiotics. In communities where CAMRSA is prevalent, ophthalmologists should obtain microbial cultures and sensitivity studies to help guide antibiotic therapy for severe ophthalmic infections.

Community-associated methicillin-resistant Staphylococcus aureus skin infections in a religious community

In September 2004, an outbreak of community-associated methicillin-resistant Staphylococcus aureus (MRSA) skin and soft tissue infections (SSTI) was reported among members of a religious community. We conducted a retrospective cohort study on all 175 community members; performed a nasal carriage survey, and environmental swab testing. We identified 24 MRSA cases (attack rate 14%). In multivariate analysis, sauna use [odds ratio (OR) 19.1, 95% confidence interval (CI) 2.7-206.1] and antimicrobial use within 12 months before infection (OR 11.7, 95% CI 2.9-47.6) were risk factors for infection. MRSA nasal carriage rate was 0.6% (1/174). Nine of 10 clinical isolates and an isolate from an administrative office within the community had the pulsed-field gel electrophoresis type USA300. Targeted hygiene improvement, wound care, and environmental cleaning were implemented. We describe the first reported outbreak of MRSA SSTI in a religious community. Adherence to appropriate personal and environmental hygiene might be critical factors in controlling transmission.

Carriage of methicillin-resistant Staphylococcus aureus in a Queensland Indigenous community

OBJECTIVE

To determine the prevalence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) carriage and infection among children living in an Indigenous community in Queensland.

DESIGN, SETTING AND PARTICIPANTS

Swabs for culture of S. aureus were collected from the nose, throat and skin wounds of primary school children.

MAIN OUTCOME MEASURES

MRSA carriage, antibiotic sensitivity, genotype, and presence of the virulence factor Panton-Valentine leukocidin (PVL); and epidemiological risk factors for MRSA carriage.

RESULTS

92 (59%) of 157 eligible children were included in the study. Twenty-seven (29%) carried S. aureus; 14 of these (15% of total) carried MRSA. MRSA was isolated from 29% of wound swabs, 8% of nose swabs, and 1% of throat swabs. Fourteen of 15 MRSA isolates were sensitive to all non-beta-lactam antibiotics tested. Eight children (9%) carried CA-MRSA clonal types: six carried the Queensland clone (ST93), and two carried the South West Pacific clone (ST30). All these isolates carried the virulence factor PVL. The remaining six children carried a hospital-associated MRSA strain (ST5), negative for PVL.

CONCLUSIONS

We have identified a high prevalence of CA-MRSA carriage in school children from a Queensland Indigenous community. In this setting, antibiotics with activity against CA-MRSA should be considered for empiric therapy of suspected staphylococcal infection. Larger community-based studies are needed to improve our understanding of the epidemiology of CA-MRSA, and to assist in the development of therapeutic guidelines for this important infection.

Contrasting pediatric and adult methicillin-resistant Staphylococcus aureus isolates

Children may share a reservoir of MRSA strains that have an antimicrobial drug resistance profile distinct from that of adults.

We performed a prospective study of all inpatient and outpatient methicillin-resistant Staphylococcus aureus (MRSA) isolates identified at the University of Chicago Hospitals from November 2003 through November 2004. Differences in resistance to non–β-lactam antimicrobial drugs were determined after stratification of the 578 MRSA isolates into 4 groups by patient age (pediatric vs. adult) and onset location (community vs. hospital). Non–β-lactam resistance was significantly greater among the 288 adult than the 177 pediatric community-associated isolates for erythromycin (93.2 vs. 87.0%, p = 0.03), clindamycin (51.8 vs. 7.3%, p<0.001), ciprofloxacin (62.1 vs. 10.7%, p<0.001), gentamicin (11.1 vs. 1.1%, p<0.001), and tetracycline (19.9 vs. 6.4%, p<0.001). In contrast, hospital-associated MRSA isolates from children and adults had similar rates of non–β-lactam antimicrobial drug resistance. In our region, clindamycin is an appropriate empiric therapy of community-associated MRSA infection in children but should be used with caution in adults.

Managing methicillin-resistant staphylococci: a paradigm for preventing nosocomial transmission of resistant organisms

Multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), are endemic in healthcare settings in the United States and many other countries of the world. Nosocomial transmission of MRSA serves as a source of hospital outbreaks, and recent reports of vancomycin-resistant S aureus strains in the United States emphasize the need for better control of MRSA and other resistant bacteria within healthcare settings. Colonization with S aureus or MRSA is relatively common in both healthy and hospitalized individuals, most often involves the anterior nares, and is frequently asymptomatic. Colonization increases risk of infection. Patient-to-patient transmission of MRSA within healthcare settings primarily occurs via carriage on the hands of healthcare workers. The Society for Healthcare Epidemiology of America (SHEA) has developed guidelines for the prevention of transmission of MRSA and vancomycin-resistant enterococci within healthcare settings, and chief among the recommendations is an emphasis on adherence to hand hygiene guidelines. Other measures that may prevent the nosocomial transmission of MRSA include improved antibiotic stewardship, staff cohorting, maintenance of appropriate staffing ratios, reductions in length of hospital stays, contact isolation, active microbiologic surveillance, and better staff education. Currently, the efficacy of many of these individual infection control interventions remain in doubt. Many studies reporting improvement in infection control outcomes (eg, reduced transmission, decreasing prevalence) involve simultaneous institution of several of these measures, making it impossible to tease out the effects of any of the individual components. Nonetheless, the best approach in the current environment probably involves hand hygiene plus a careful assessment of an institution's particular circumstances, applying more aggressive procedures such as patient isolation, staff cohorting, and active surveillance cultures, as indicated.

Managing methicillin-resistant staphylococci: a paradigm for preventing nosocomial transmission of resistant organisms

Multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), are endemic in healthcare settings in the United States and many other countries of the world. Nosocomial transmission of MRSA serves as a source of hospital outbreaks, and recent reports of vancomycin-resistant S aureus strains in the United States emphasize the need for better control of MRSA and other resistant bacteria within healthcare settings. Colonization with S aureus or MRSA is relatively common in both healthy and hospitalized individuals, most often involves the anterior nares, and is frequently asymptomatic. Colonization increases risk of infection. Patient-to-patient transmission of MRSA within healthcare settings primarily occurs via carriage on the hands of healthcare workers. The Society for Healthcare Epidemiology of America (SHEA) has developed guidelines for the prevention of transmission of MRSA and vancomycin-resistant enterococci within healthcare settings, and chief among the recommendations is an emphasis on adherence to hand hygiene guidelines. Other measures that may prevent the nosocomial transmission of MRSA include improved antibiotic stewardship, staff cohorting, maintenance of appropriate staffing ratios, reductions in length of hospital stays, contact isolation, active microbiologic surveillance, and better staff education. Currently, the efficacy of many of these individual infection control interventions remain in doubt. Many studies reporting improvement in infection control outcomes (e.g., reduced transmission, decreasing prevalence) involve simultaneous institution of several of these measures, making it impossible to tease out the effects of any of the individual components. Nonetheless, the best approach in the current environment probably involves hand hygiene plus a careful assessment of an institution's particular circumstances, applying more aggressive procedures such as patient isolation, staff cohorting, and active surveillance cultures, as indicated.

Can pre-operative skin marking transfer methicillin-resistant Staphylococcus aureus between patients?

National guidelines state that in patients undergoing operations the site of the procedure should be marked. In clinical practice the same marker is used repeatedly. We are not aware of any investigation regarding the theoretical risk of transferring organisms such as methicillin-resistant Staphyloccocus aureus (MRSA) between patients by a skin marker.

In an experimental setting, Penflex and Viomedex skin markers were tested 30 times each after contaminating them with a standard inoculum of MRSA. The survival of the organism on the tip of the markers was assessed by culture on MRSA-indicator nutrient agar plates at 0, 5, 15 and 60 minutes, 24 and 48 hours and at 1, 2, and 3 weeks after contamination.

There was a significant difference between the markers, with the Penflex showing no survival of MRSA after 15 minutes whereas the Viomedex product continued to produce MRSA cultures for up to three weeks.

Commensals upon us

A battle to control and curtail bacterial infectious diseases is being waged in our hospitals and communities through antibiotic therapies and vaccines targeting specific species. But what effects do these interventions have on the epidemiology of infections caused by the organisms that are part of our natural microbial flora? Gram-positive and gram-negative bacteria appear as new disease agents from among commensal flora. These include vancomycin resistant enterococci (VRE), community-associated methicillin resistant Staphylococcus aureus (CA-MRSA), non-vaccine invasive serotypes of Streptococcus pneumoniae, new strains of non-type b Haemophilus influenzae and multi-drug resistant Escherichia coli. These examples illustrate how clinical improvements and widespread use and misuse of antibiotics have pushed evolution, allowing normally non-pathogenic strains to become infectious disease threats to human health.

Emergence of Community-Associated Methicillin-Resistant Staphylococcus aureus USA300 Genotype as a Major Cause of Health Care--Associated Blood Stream Infections

BACKGROUND

Whether community-associated methicillin-resistant Staphylococcus aureus (MRSA) genotypes (e.g., USA300) are a major cause of bloodstream infections (BSIs) and health care-associated infections has been poorly defined.

METHODS

Consecutive MRSA isolates recovered from patients with BSIs were prospectively collected at an urban public hospital. Molecular typing studies were performed. Prevalence and risk factors for the MRSA USA300 genotype were assessed.

RESULTS

One hundred thirty-two cases of MRSA BSI were documented over 7.5 months in 2004 (incidence, 6.79 per 1000 admissions); 116 isolates were available for genotyping. Characteristics of the 116 evaluable cases included: a mean age 47 years; 62% were male, 82% were African American, and 22% were HIV seropositive. The crude in-hospital mortality rate was 22%. In 107 cases (92%), there was contact with a health care facility within the year prior to infection, and a nosocomial infection (defined as positive blood culture results obtained >48 h after admission) occurred in 49 cases (42%). PFGE demonstrated that 39 (34%) of the 116 isolates were the MRSA USA300 genotype; 34 (29%) were USA100; 42 (36%) were USA500; and 1 (1%) was USA800. MRSA USA300 accounted for 28% of health care-associated BSIs and 20% of nosocomial MRSA BSIs. In multivariate analysis, isolation of the USA300 genotype was associated with injectiondrug use (OR, 3.67; 95% CI, 1.10-12.28) and skin and soft tissue infection (OR, 4.26; 95% CI, 1.08-16.84). Patients who resided in long-term care facilities (OR, 0.09; 95% CI, 0.01-0.82) and those who were treated with antimicrobials in the prior year were less likely to have MRSA USA300 genotype recovered (OR, 0.10; 95% CI, 0.02-0.49).

CONCLUSIONS

MRSA USA300 genotype, the predominant cause of community-associated MRSA infections in our area (Atlanta, GA), has now emerged as a significant cause of health care-associated and nosocomial BSI. MRSA USA300 as a nosocomial pathogen presents new challenges to infection control programs.

Community-associated methicillin-resistant Staphylococcus aureus: reconsideration of therapeutic options

Methicillin resistance, long recognized as characteristic of nosocomial Staphylococcus aureus, has increasingly been identified in community-acquired strains in the past 15 years. The genotypes of community-associated methicillin-resistant S. aureus (MRSA) are different from nosocomial strains, and unlike nosocomial strains, they have a distinctive methicillin-resistance chromosomal cassette (designated type IV), are usually susceptible to multiple classes of antimicrobials other than beta-lactams, carry a distinctive virulence factor (the Panton-Valentine leukocidin), cause mainly skin and soft tissue infection and less frequently, necrotizing pneumonia, and involve predominantly children and young adults. Outbreaks have been reported in certain segments of the population (eg, football players, wrestlers, prison inmates, and native people) that often do not have the established risk factors for MRSA. However, these strains have also caused infections likely acquired in an institutional health care setting. Delay in starting appropriate antibiotic therapy for severe infections caused by MRSA can be life-threatening. This requires a reconsideration of the empiric choice of an anti-staphylococcal beta-lactam for seriously ill patients with suspected community-associated S. aureus infections.

Characterization of a strain of community-associated methicillin-resistant Staphylococcus aureus widely disseminated in the United States

A highly stable strain of Staphylococcus aureus with a pulsed-field gel electrophoresis type of USA300 and multilocus sequence type 8 has been isolated from patients residing in diverse geographic regions of the United States. This strain, designated USA300-0114, is a major cause of skin and soft tissue infections among persons in community settings, including day care centers and correctional facilities, and among sports teams, Native Americans, men who have sex with men, and military recruits. The organism is typically resistant to penicillin, oxacillin, and erythromycin (the latter mediated by msrA) and carries SCCmec type IVa. This strain is variably resistant to tetracycline [mediated by tet(K)]; several recent isolates have decreased susceptibility to fluoroquinolones. S. aureus USA300-0114 harbors the genes encoding the Panton-Valentine leucocidin toxin. DNA sequence analysis of the direct repeat units within the mec determinant of 30 USA300-0114 isolates revealed differences in only a single isolate. Plasmid analysis identified a common 30-kb plasmid that hybridized with blaZ and msrA probes and a 3.1-kb cryptic plasmid. A 4.3-kb plasmid encoding tet(K) and a 2.6-kb plasmid encoding ermC were observed in a few isolates. DNA microarray analysis was used to determine the genetic loci for a series of virulence factors and genes associated with antimicrobial resistance. Comparative genomics between USA300-0114 and three other S. aureus lineages (USA100, USA400, and USA500) defined a set of USA300-0114-specific genes, which may facilitate the strain's pathogenesis within diverse environments.

MRSA—the tip of the iceberg

Methicillin-resistant Staphylococcus aureus (MRSA) strains cause serious nosocomial infections all over the world. Overall, approximately 20% of S. aureus isolates in Europe are reported as methicillin-resistant, whereas in US hospitals the prevalence ranges from 33% to 55%. The past few years have also witnessed an increase in life-threatening community-acquired infections caused by Panton-Valentine leukocidin-producing MRSA in the USA. Increasing use of glycopeptides for treatment of community-acquired MRSA infections may result in higher rates of glycopeptide resistance. Since 1996, five vancomycin-intermediate S. aureus (VISA; vancomycin MIC = 8-16 mg/L) strains have been identified in Europe, Asia and the USA, and vancomycin-resistant S. aureus (VRSA) strains (vancomycin MIC > or = 32 mg/L) have also been reported in the USA between 2002 and 2005. Most infections with VISA and VRSA have occurred in a setting of heavy prior use of glycopeptides and other antimicrobial agents. Emergence of reduced vancomycin susceptibility in S. aureus increases the possibility that currently available antimicrobial agents may become ineffective for treating systemic infections, especially bacteraemia, endocarditis and osteomyelitis. Ceftobiprole is a novel broad-spectrum cephalosporin with expanded activity against Gram-positive bacteria, including MRSA. Ceftobiprole is refractory to the development of endogenous resistance both in vitro and in vivo. The additional activity of ceftobiprole against MRSA strains makes it a potentially important addition to currently available agents.

Emergence of community-associated methicillin-resistant Staphylococcus aureus USA 300 clone as a cause of health care-associated infections among patients with prosthetic joint infections

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as an important cause of staphylococcal infections, but there have been little data on whether CA-MRSA causes health care-associated infections.

METHODS

A case-control study was performed to identify risk factors for prosthetic joint infections (PJI). Antibiograms of isolates associated with PJI were reviewed. Molecular typing of available MRSA isolates was done using pulsed field gel electrophoresis (PFGE). Nares cultures of health care workers who provided care to those orthopedic patients were obtained.

RESULTS

Over a 13-month period (January 2003-January 2004), 9.5% of patients with prosthetic hip (THA) or knee (TKA) joint surgery developed PJI (7 TKA and 2 THA). The mean time to development of PJI was 20 days. Five infections were caused by CA-MRSA and 3 by methicillin-susceptible S aureus; one was culture negative. All CA-MRSA isolates had identical antibiograms (resistant to beta-lactams and erythromycin; susceptible to clindamycin, trimethoprim-sulfamethoxazole, rifampin, gentamicin, levofloxacin, and vancomycin). Molecular typing of 2 available CA-MRSA isolates revealed that these were the USA300 clone; these isolates were PVL+ and carried SCCmec IV. CA-MRSA was not recovered from nares cultures from 31 health care workers. In multivariate analysis, TKA (OR, 8.1; 95% CI: 1.3-48.1) and surgery time >180 minutes (OR, 7.4; 95% CI: 1.4-39.6) were associated with PJI.

CONCLUSION

We have demonstrated that the CA-MRSA USA300 clone is no longer just a cause of community-acquired infections but has also emerged as a cause of health care-associated infections, causing PJI at our institution.