Clinical and Laboratory Features of Community-Associated Methicillin-ResistantStaphylococcus aureus:Is It Really New?

Emergence of Community-Associated Methicillin-ResistantStaphylococcus aureusInfection Among Patients With End-Stage Renal Disease

Objective.

To evaluate the frequency of infections due to community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA) strains among our patients with end-stage renal disease.

Design.

Prospective observational clinical and laboratory study of patients in 2005. Molecular features of isolates recovered from these patients were compared with those of isolates recovered in 2000 from patients with end-stage renal disease.

Setting.

A 600-bed urban academic medical center.

Patients.

Thirty-two patients with end-stage renal disease and MRSA infection at the time of hospitalization from 2005 were evaluated. For comparison, laboratory analysis was performed for 17 MRSA isolates recovered from patients with end-stage renal disease in 2000.

Results.

The patients from 2005 were more likely than the patients from 2000 to have infection with strains that carried the staphylococcal cassette chromosome (SCC)mectype IV complex (50% vs 11.8%; relative risk, 4.25 [95% confidence interval, 1.17-25.98];P= .012) and the Panton-Valentine leukocidin toxin genes (25% vs 0%;P= .038). Eight patients from 2005 were infected with a strain that is identical to MRSA clone USA300 in terms of molecular type and presence of SCCmectype IV and Panton-Valentine leukocidin genes. Among the patients from 2005, those infected with SCCmectype IV strains (ie, CA-MRSA strains) and those infected with SCCmectype II strains (ie, healthcare-associated MRSA [HA-MRSA] strains) were similar with respect to demographic characteristics, risk factors, and outcomes.

Conclusions.

We documented an increased proportion of infections with CA-MRSA strains, including clone USA300, among our population of patients undergoing dialysis. Patients infected with CA-MRSA strains and HA-MRSA strains were similar with respect to presenting illness and outcomes.

Diagnostic and therapeutic evaluation of community-acquired methicillin-resistant Staphylococcus Aureus (MRSA) skin and soft tissue infections in the emergency department

BACKGROUND

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections commonly present as skin and soft-tissue infections (SSTIs). Treatment often includes incision and drainage with or without adjunctive antibiotics. Emergency department (ED) pharmacists wished to provide specific data to emergency physicians to better inform antibiotic choices for patients with SSTIs.

STUDY OBJECTIVES

The objectives of this study were to describe local susceptibility trends of CA-MRSA isolates obtained from patients with SSTIs and describe diagnostic and empiric therapeutic management of CA-MRSA SSTIs among ED health care providers at University of Utah Hospitals and Clinics.

METHODS

Susceptibility of all unique CA-MRSA SSTI isolates for 2008 were identified and compiled into an antibiogram. ED providers evaluated their diagnostic and treatment habits using a self-assessment questionnaire, which was verified against charted information documented in the electronic medical records for patients presenting to the ED with a CA-MRSA SSTI.

RESULTS

The ED antibiogram indicated that 57/58 (98%) CA-MRSA SSTI isolates were susceptible to sulfamethoxazole/trimethoprim (SMX/TMP); 50/58 (86%) isolates were susceptible to tetracycline, and 47/58 (81%) isolates were susceptible to clindamycin. Incision and drainage were performed in 23/25 (92%) patient cases, which was consistent with providers' perceived habits (100%). SMX/TMP monotherapy was preferred among 23/35 (66%) providers, however, SMX/TMP combined with cephalexin was the antibiotic regimen prescribed in 9/22 (41%) patient cases.

CONCLUSIONS

Cephalexin was often added to cover for potential cellulitis due to Streptococcus spp., however, the surrounding erythema may simply be an extension of the CA-MRSA infection. Department-specific antibiograms are useful in guiding empiric antibiotic selection and may help providers judiciously prescribe antibiotics only when necessary.

Public health surveillance for methicillin-resistant Staphylococcus aureus: comparison of methods for classifying health care- and community-associated infections

OBJECTIVES

We compared 3 methods for classifying methicillin-resistant Staphylococcus aureus (MRSA) infections as health care associated or community associated for use in public health surveillance.

METHODS

We analyzed data on MRSA infections reported to the Michigan Department of Community Health from October 1, 2004, to December 31, 2005. Patient demographics, risk factors, infection information, and susceptibility were collected for 2151 cases. We classified each case by the health care risk factor, infection-type, and susceptibility pattern methods and compared the results of the 3 methods.

RESULTS

Demographic, clinical, and microbiological variables yielded similar health care-associated and community-associated distributions when classified by risk factor and infection type. When 2 methods yielded the same classifications, the overall distribution was similar to classification by 3 methods. No specific combination of 2 methods was superior.

CONCLUSIONS

MRSA categorization by 2 methods is more accurate than it is by a single method. The health care risk factor and infection-type methods yield comparable classification results. Accuracy is increased by using more variables; however, further research is needed to identify the optimal combination.

Community-associated methicillin-resistant Staphylococcus aureus mediastinitis

Community-associated methicillin (meticillin)-resistant Staphylococcus aureus (CA-MRSA) continues to emerge as a cause of serious infections, chiefly of the skin and soft tissues. We present the first documented case of CA-MRSA mediastinitis in an adult. Blood and mediastinal isolates were characterized as CA-MRSA by pulsed-field gel electrophoresis and susceptibility testing.

The changing susceptibilities of methicillin-resistant Staphylococcus aureus at a midwestern hospital: the emergence of "community-associated" MRSA

BACKGROUND

The emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has been well described; however, few studies have reviewed long-term hospital-wide data.

METHODS

This retrospective study of adult patients used the first culture per patient per visit positive for MRSA for 1996 to 2005. Isolates were categorized as community-associated or health care-associated phenotype based on antibiotic susceptibilities. chi(2) tests for trend and linear regression analyses were performed.

RESULTS

The annual prevalence of CA-MRSA increased significantly over the 10-year study period (from 43 of 507 [8.9%] MRSA cultures in 1996 to 672 of 1697 [39.6%] MRSA cultures in 2005; P < .01). The proportion of MRSA cultures obtained within 48 hours of hospital admission increased from 50.5% to 79.5% (P < .01). The median age of patients with MRSA decreased, from 60 to 49 years (P < .01). Among the CA-MRSA cases, the proportion of non-Caucasian patients increased from 30.2% to 60.4% (P < .01) and the proportion of patients categorized as low socioeconomic status increased from 25.6% to 35.6% (P < .01). Significant consistent trends were not observed for patient sex or body sites of the cultures.

CONCLUSION

An increasing number of MRSA with a community-associated phenotype occurred during the 10-year study period. Patterns of decreasing age, increasing non-Caucasian races, and decreasing socioeconomic status were observed among patients with MRSA.

Evidence based approach to the treatment of community-associated methicillin-resistant Staphylococcus aureus

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections have increased dramatically over the last two decades. The types of infections can range from complicated skin and skin structure infections (cSSSI) to pneumonia and endocarditis. Oral antimicrobial therapy, such as trimethoprim-sulfamethoxazole, clindamycin, long-acting tetracyclines, or linezolid may provide enhanced benefit to those with uncomplicated cutaneous lesions when used in conjunction with incision and drainage in an outpatient setting. However, resistance, susceptibilities, patient-specific circumstances, and adverse effects can impact a healthcare professional's choice of antibiotics. In patients with complicated infections requiring hospitalization or parenteral treatment, vancomycin remains the drug of choice, even though increased resistance and decreased efficacy have crept into clinical practice. Linezolid, quinupristin/dalfopristin, daptomycin, and tigecycline are alternative intravenous agents for the treatment of CA-MRSA. Investigational agents such as dalbavancin, telavancin, oritivancin, iclaprim, ceftobiprole, ceftaroline, and others may expand our therapeutic armamentarium for the treatment of infections caused by CA-MRSA in the future.

Synergy between gemifloxacin and trimethoprim/sulfamethoxazole against community-associated methicillin-resistant Staphylococcus aureus

OBJECTIVES

The rapid emergence of methicillin-resistant Staphylococcus aureus from the community (CA-MRSA) presents difficulties in making treatment choices. We evaluated whether combining another orally available agent commonly used to treat CA-MRSA with gemifloxacin would enhance gemifloxacin activity against CA-MRSA.

METHODS

Fifty strains of SCCmec IV, agr group 1, Panton-Valentine leucocidin-positive CA-MRSA were evaluated for susceptibilities to gemifloxacin, trimethoprim/sulfamethoxazole, doxycycline, levofloxacin, rifampicin, clindamycin and erythromycin. Twenty of these strains were evaluated for the potential for synergy between gemifloxacin and trimethoprim/sulfamethoxazole, clindamycin and rifampicin by time-kill analysis. Two strains were further evaluated in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model.

RESULTS

In time-kill analyses, gemifloxacin combined with trimethoprim/sulfamethoxazole produced additivity (6/20) or synergy (11/20) in 85% of the isolates tested. The addition of clindamycin to gemifloxacin showed additivity (3/20) or synergy (2/20) in 25% of the isolates. All isolates displayed indifference to the combination of gemifloxacin and rifampicin. In the PK/PD model, combining gemifloxacin and trimethoprim/sulfamethoxazole provided potent and sustained bactericidal activity to detection limits of 2 log(10) cfu/mL by 48 h; gemifloxacin combined with clindamycin or with rifampicin killed to detection limits by 56 h or later. One isolate developed efflux-mediated resistance to gemifloxacin at 96 h with gemifloxacin monotherapy. All combinations prevented the emergence of this resistance.

CONCLUSIONS

Synergy or additivity was demonstrated by time-kill analysis between gemifloxacin and trimethoprim/sulfamethoxazole in most isolates tested. In the PK/PD model, the addition of trimethoprim/sulfamethoxazole, clindamycin and rifampicin enhanced the activity of gemifloxacin against CA-MRSA and suppressed the emergence of resistance to gemifloxacin.

Comparative activity of telavancin against isolates of community-associated methicillin-resistant Staphylococcus aureus

OBJECTIVES

This study compared the activity of telavancin, a novel multivalent lipoglycopeptide with rapid bactericidal activity, with those of five standard antibiotics for methicillin-resistant Staphylococcus aureus (MRSA) against isolates of community-associated MRSA (CA-MRSA).

METHODS

Microdilution tests performed according to CLSI guidelines using cation-adjusted Mueller-Hinton broth were used to determine the MIC values of telavancin, quinupristin/dalfopristin, vancomycin, trimethoprim/sulfamethoxazole, linezolid and daptomycin versus 60 CA-MRSA isolates. MBC values of telavancin were determined according to CLSI guidelines and American Society for Microbiology standards. PFGE was performed using the restriction enzyme SmaI. Samples from three predominant pulsed-field types were typed by multilocus sequence typing. Staphylococcal cassette chromosome mec typing was determined by multiplex PCR. The Panton-Valentine leucocidin (PVL) genes (lukS-PV and lukF-PV) were identified by PCR.

RESULTS

The telavancin MIC90 and MBC90 values for this collection of 60 CA-MRSA isolates were 0.5 and 1 mg/L, respectively, with MIC and MBC values both ranging from 0.25 to 1 mg/L. Telavancin was found to be bactericidal in this study, as its MBC was no more than 2-fold higher than its MIC for all CA-MRSA isolates tested except one. (A single isolate yielded an MBC/MIC ratio of 4.) PVL- and non-PVL-producing strains demonstrated similar susceptibility to telavancin and comparator agents.

CONCLUSIONS

Based on in vitro activity, telavancin should be an effective agent against CA-MRSA.

Prevalence of nasal colonization among patients with community-associated methicillin-resistant Staphylococcus aureus infection and their household contacts

OBJECTIVE

To evaluate the prevalence of colonization among patients with community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infection and their household contacts.

DESIGN

Prospective, observational laboratory study of nasal colonization among patients and their household members from September 15, 2004, to February 20, 2006.

SETTING

A 600-bed, urban, academic medical center.

PATIENTS

Fifty-one patients who presented with CA-MRSA infections and 49 household members had cultures of nasal swab specimens performed.

RESULTS

Skin and soft-tissue infections were seen in 50 patients (98%) and 2 household members. Twenty-one (41%) of 51 patients and 10 (20%) of 49 household members were colonized with MRSA. An additional 5 patients (10%) and 12 household members (24%) were colonized with methicillin-susceptible Staphylococcus aureus. Most MRSA isolates (95%; infective and colonizing) carried the staphylococcal cassette chromosome mec type IV complex, and 67% represented a single clone, identical to USA 300. Of the colonized household members, 5 had isolates related to the patients' infective isolate.

CONCLUSIONS

The frequency of CA-MRSA colonization among household members of patients with CA-MRSA infections is higher than rates reported among the general population. Among colonized household members, only half of the MRSA strains were related to the patients' infective isolate. Within the same household, multiple strains of CA-MRSA may be present.

Methicillin-resistant Staphylococcus aureus colonization in veterinary personnel

TOC Summary: Prevalence of colonization was 6.5%, and employment within a large-animal practice was a significant risk factor.

Methicillin-resistant Staphylococcus aureus (MRSA) was isolated from nares of 27/417 (6.5%) attendees at an international veterinary conference: 23/345 (7.0%) veterinarians, 4/34 (12.0%) technicians, and 0/38 others. Colonization was more common for large-animal (15/96, 15.6%) than small-animal personnel (12/271, 4.4%) or those with no animal patient contact (0/50) (p<0.001). Large-animal practice was the only variable significantly associated with colonization (odds ratio 2.9; 95% confidence interval 1.2–6.6). Pulsed-field gel electrophoresis identified 2 predominant clones with similar distribution among veterinarians as previously reported for horses and companion animals. Canadian epidemic MRSA-2 (CMRSA) was isolated from 11 small-animal and 2 large-animal personnel from the United States (n = 12) and Germany (n = 1). In contrast, CMRSA-5 was isolated exclusively from large-animal personnel (p<0.001) in the United States (n = 10), United Kingdom (n = 2), and Denmark (n = 1). MRSA colonization may be an occupational risk for veterinary professionals.

Emerging Options for Treatment of Invasive, Multidrug-ResistantStaphylococcus aureusInfections

Limited established treatment options exist for the treatment of serious, invasive infections caused by multidrug-resistant Staphylococcus aureus, most notably nosocomially acquired methicillin-resistant S. aureus (MRSA). Although vancomycin represents the gold standard for therapy of such invasive infections, reports of increasing in vitro resistance to vancomycin, combined with reports of clinical failures (with this and other antistaphylococcal agents), underscore the need for alternative therapies. Older agents with favorable in vitro activity available in both oral and intravenous dose forms include trimethoprim-sulfamethoxazole and clindamycin. Limited clinical data exist to support their routine use as initial therapy in the treatment of invasive disease. However, these and other options (e.g., tetracyclines) are being reexplored in the setting of increasing concern over MRSA acquired in the community setting. Newer treatment options for MRSA include linezolid, quinupristin-dalfopristin, daptomycin, and tigecycline. With the exception of linezolid, these newer agents require intravenous administration. Combination therapy may be considered in select invasive diseases refractory to standard monotherapies. These diseases include infections such as endocarditis, meningitis, and prosthetic device infections. Additional alternatives to vancomycin are under clinical investigation. Those in later stages of development include oritavancin, dalbavancin, telavancin, and ceftobiprole.

Shift in Staphylococcus aureus clone linked to an infected tattoo

A retrospective investigation of skin and soft tissue infections caused by community-associated methicillin-resistant Staphylococcus aureus (MRSA) strains among inmates in a Wisconsin correctional facility suggested a shift in MRSA genotype. Case timeline indicated a displacement of USA400 clone by USA300 clone. The USA300 index case was associated with an infected new tattoo.