Understanding The Impact Of MRSA On Limb Preservation

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Continuing Education Course #154 — July 2007

I am pleased to introduce the latest article, “Understanding The Impact Of MRSA On Limb Preservation,” in our CE series. This series, brought to you by the North American Center for Continuing Medical Education (NACCME), consists of complimentary CE activities that qualify for one continuing education contact hour (.1 CEU). Readers will not be required to pay a processing fee for this course.
Methicillin resistant Staphylococcus aureus (MRSA) continues to increase in both hospital and community settings. Accordingly, Loan Lam, DPM, Peter Blume, DPM, and Michael Palladino, DPM, discuss the range of available antibiotic options and the unique challenges of limb salvage in the face of MRSA.
At the end of this article, you’ll find a 10-question exam. Please mark your responses on the enclosed postcard and return it to NACCME. This course will be posted on Podiatry Today’s Web site (www.podiatrytoday.com) roughly one month after the publication date. I hope this CE series contributes to your clinical skills.


Jeff A. Hall
Executive Editor
Podiatry Today

INSTRUCTIONS: Physicians may receive one continuing education contact hour (.1 CEU) by reading the article on pg. 76 and successfully answering the questions on pg. 82. Use the enclosed card provided to submit your answers or log on to www.podiatrytoday.com and respond via fax to (610) 560-0502.
ACCREDITATION: NACCME is approved by the Council on Podiatric Medical Education as a sponsor of continuing education in podiatric medicine.
DESIGNATION: This activity is approved for 1 continuing education contact hour or .1 CEU.
DISCLOSURE POLICY: All faculty participating in Continuing Education programs sponsored by NACCME are expected to disclose to the audience any real or apparent conflicts of interest related to the content of their presentation.
DISCLOSURE STATEMENTS: Drs. Lam, Blume and Palladino have disclosed that they have no significant financial relationship with any organization that could be perceived as a real or apparent conflict of interest in the context of the subject of their presentation.
GRADING: Answers to the CE exam will be graded by NACCME. Within 60 days, you will be advised that you have passed or failed the exam. A score of 70 percent or above will comprise a passing grade. A certificate will be awarded to participants who successfully complete the exam.
EXPIRATION DATE: July 31, 2008
LEARNING OBJECTIVES: At the conclusion of this activity, participants should be able to:
• distinguish between community-acquired and hospital-acquired MRSA;
• discuss the increased prevalence of MRSA in diabetic foot infections;
• list the antibiotics that clinicians can use to treat skin and skin structure infections caused by CA-MRSA;
• review the literature on the use of linezolid, daptomycin and tigecycline in treating MRSA infections; and
• review key questions one should ask in the diagnostic workup of patients with limb-threatening infections.

Sponsored by the North American Center for Continuing Medical Education.

Understanding The Impact Of MRSA On Limb Preservation
Understanding The Impact Of MRSA On Limb Preservation
Understanding The Impact Of MRSA On Limb Preservation
Understanding The Impact Of MRSA On Limb Preservation
Understanding The Impact Of MRSA On Limb Preservation
Understanding The Impact Of MRSA On Limb Preservation
By Loan Lam, DPM, Peter Blume, DPM, FACFAS, and Michael Palladino, DPM, FACFAS

Given the increasing prevalence of methicillin resistant Staphylococcus aureus (MRSA), these authors discuss the differences between HA-MRSA and CA-MRSA, what the literature reveals about antibiotic therapy and keys to the diagnostic workup of these patients.
To say that methicillin-resistant Staphylococcus aureus (MRSA) is a growing problem in the healthcare setting is an understatement. Indeed, healthcare providers are diagnosing this organism at an alarming rate in severe infections of both healthy people and the immunocompromised. In 1973, the Centers for Disease Control and Prevention (CDC) reported that MRSA accounted for 2 percent of all Staphylococcus infections. In 2004, it accounted for 63 percent.1

   In both the nondiabetic and diabetic populations, Staphylococcus aureus is the most frequently isolated organism in all lower extremity infections. Some studies have noted that Staphylococcus aureus accounts for up to 76 percent of organisms isolated in the foot with 20 percent being MRSA.1,2 It now also has the dubious honor of being the most common isolate in infections that occur after vascular graft placements.3-5

   When researchers first discovered MRSA in the early 1960s, it was believed that a single clone was responsible for all MRSA isolates. The landscape has now been vastly complicated by the emergence of at least five new strains of MRSA. While researchers originally saw MRSA as only a nosocomial pathogen, new strains are emerging as community associated MRSA (CA-MRSA).

   The CDC defines CA-MRSA infections as those acquired by: people who have neither been hospitalized nor had a medical procedure in the past year; people who do not have indwelling catheters or medical devices; people with no history of previous MRSA infections or colonization; and those who are diagnosed in an outpatient setting or within 48 hours of initial hospitalization. The CDC also reports that although 25 to 30 percent of the general population is colonized with Staph aureus, 1 percent of the population is colonized with MRSA.1,2

What You Should Know About HA-MRSA And CA-MRSA

The difference between hospital-acquired MRSA (HA-MRSA) and CA-MRSA lies in their genetic makeup. All strains of MRSA have a mec-A gene, which is responsible for its drug resistance and is located on an element called staphylococcal cassette chromosome (SCCmec). There are five types of SCCmec with different variations of size and genetic makeup. CA-MRSA strains have a type IV SCCmec gene, which induces its resistance to methicillin, beta-lactams and erythromycin. However, the type IV SCCmec gene is susceptible to other drugs such as clindamycin and trimethoprim-sulfamethoxazole.6-9

   The CA-MRSA strains also produce Panton-Valentine leukocidin (PVL), a pore-forming exotoxin that researchers have shown is correlated with more febrile days and higher complications of osteomyelitis.7 Genestier, et al., discovered that PVLs targeted and caused cell death in neutrophils and lymphocytes by disrupting the mitochondria. This also induced the release of certain neutrophil factors that cause inflammation and tissue loss.

   Researchers have postulated that this mechanism results in the high incidence of CA-MRSA found in skin and soft tissue infections (SST).8 Naimi, et al., reported that 75 percent of CA-MRSA isolates were found in SST infections as opposed to 37 percent of HA-MRSA found in SST infections.6

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