Keys To Addressing MRSA In The Diabetic Foot
As diabetic infections continue to evolve and become more resistant to antibiotics, having a comprehensive treatment plan for methicillin resistant Staphylococcus aureus (MRSA) is crucial. These authors present a guide to current antibiotic options and offer two illuminating case studies of patients with diabetes and MRSA.
Since the first published reports of methicillin-resistant Staphylococcus aureus (MRSA) in the early 1960s, MRSA has seen a steady increase in prevalence and growing antibiotic resistance. The superbug reached endemic proportions in hospitals worldwide by 1990 after being a major problem in Europe in the 1970s.
This species of Staphylococcus has seen division into two distinct organisms, healthcare-associated MRSA (HA-MRSA) and community-associated MRSA (CA-MRSA). Resistance continues to be a factor with both HA-MRSA and CA-MRSA, with some strains showing resistance to even vancomycin and linezolid (Zyvox, Pfizer). The Centers for Disease Control and Prevention (CDC), in a review of cases from 2005 to 2008, reported a decline in healthcare-associated MRSA (HA-MRSA) by almost 30 percent.1 Despite this trending decline in healthcare-associated infections, CA-MRSA strains progress without a decline in sight.
This transition has not only had a greater impact on the general population but clinicians are seeing an increasing impact on the diabetic population, especially in regard to those with diabetic foot ulcers, wounds and infections.
In a 2003 study, Dang and colleagues studied the prevalence of pathogenic organisms in foot ulcers in patients with diabetes and compared the results with a similar study three years earlier.2 Their findings demonstrated a twofold increase in the prevalence of MRSA in diabetic foot infections within a three-year span. Further study by Yates and co-workers concluded that wound/ulcer chronicity and chronic renal disease each independently predispose patients to MRSA infections.3 The researchers also found that prior hospitalization and chronicity of wounds were both associated with the increased presence of polymicrobial infection, often involving gram-negative organisms.
For these reasons, in order to optimize initial antibiotic regimens, clinicians should raise their index of suspicion for MRSA in populations presenting with chronic ulcers, chronic wounds, a prior history of MRSA and positive carrier traits such as nasal swabs that are positive for MRSA.
Aerobic, gram-positive cocci, especially Staphylococcus aureus, have been the predominant pathogenic organisms in diabetic foot infections. Indeed, the prevalence of MRSA and its growing resistance to antibiotic treatment regimens should be warning signs in regard to appropriate antibiotic selection when dealing with these types of infections. It is also important to remember that more severe diabetic foot infections are most often polymicrobial. Accordingly, coverage of only MRSA would be inadequate. Given the current data and the known risk indicators for MRSA, one can implement a guided approach to antibiotic selection prior to and after cultures.
Wound cultures have been a primary indicator of bacterial presence or bioburden. The Infectious Diseases Society of America (IDSA) recommends obtaining cultures from a deep soft tissue specimen for more appropriate and accurate isolation of the infectious organism.4 Prior to final culture results, the initial management of the diabetic foot infection is often dictated by the severity of the infection, especially in the presence of an ulcer or wound. The severity of infection can range from skin and soft tissue infections, abscess and cellulitis to osteomyelitis and necrotizing infections. When necessary, one should always recognize the importance of adequate surgical debridement in conjunction with initiating an appropriate antibiotic regimen. Clinicians may tailor this regimen upon final confirmation of the pathogenic organisms with appropriate soft tissue cultures.