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Diabetic Foot Infection Classification System Validated

The Infectious Diseases Society of America (IDSA) has designed a classification system for foot infections in patients with diabetes to provide better outcomes for these patients. “Foot wounds are among the most common and severe complications of diabetes and are now the most frequent cause for diabetes-associated hospitalization,” write Lawrence A. Lavery, DPM, MPH, of the Scott and White Hospital, Texas A&M University Health Science Center College of Medicine in Temple, and colleagues. “About one-half of these wounds become clinically infected during the course of therapy…. Ascertaining the severity of infection should help clinicians determine what treatments are needed, as well as in what environment and how urgently they must be provided.”

In 2004, the IDSA and the International Working Group on the Diabetic Foot (IWGDF) each published a comprehensive set of guidelines for the management of diabetic foot infections, including a classification scheme for infection severity. Both systems first divide wounds by whether they are clinically infected based on the presence of purulent secretions or local or systemic signs of inflammation or infection. Infected wounds are further classified as mild, moderate, or severe, based on the size (especially of any cellulitis) and depth (or level of tissue involved) of the infection, and on the presence of systemic manifestations of infection or metabolic instability.

Although these systems were developed by an international consensus of experts in various fields, no studies to date have validated their ability to predict clinical outcomes of diabetic foot infection. Using a database developed for a prospective diabetes-related foot care management program, the investigators evaluated the ability of the IDSA-IWGDF classification scheme to predict adverse outcomes.

In this longitudinal study of 1666 persons with diabetes, 27 (18%) of all infections were severe, and 50 patients required a lower extremity amputation of some type. Increasing infection severity on the IDSA-IWGDF classification scheme was associated with an observed trend toward an increased risk for amputation (?2 test for trend, 108.0; P < .001), higher-level amputation (?2 test for trend, 113.3; P < .001), and lower-extremity–related hospitalization (?2 test for trend, 118.6; P < .001).

Increasing severity of infection was also associated with more-frequent lower extremity comorbidities, such as peripheral neuropathy and arterial vascular disease, and with deeper infection-related bone and joint disease.

“The Infectious Diseases Society of America’s foot infection classification system may be a useful tool for grading foot infections,” the authors write. “It suggests that persons with mildly infected or noninfected wounds are highly unlikely to require hospitalization, develop osteomyelitis, or undergo amputation.”

The authors suggest that determining the severity of a foot infection in a patient with diabetes may help the clinician decide on hospitalization, whether to use parenteral or oral antibiotics, and how urgently surgery or other treatments need to be performed.
“We believe that the simplicity of determining the components of this system, coupled with the strong suggestion of its clinical utility, may make it a useful instrument in helping clinicians determine which of their patients are at the highest risk for adverse outcomes from a diabetic foot infection,” the authors conclude. “Perhaps more aggressive medical, surgical, and adjunctive measures could be directed at these patients, with the hope that this would improve their foot salvaging outcome. This system should also be useful for clinical research studies, to allow for comparisons among patients enrolled in various investigations.”
Diabetes is the most common underlying reason for lower extremity amputation in the developed world, and improved identification and classification of diabetic foot infections may promote improved care and reduced morbidity. To this end, the IDSA has presented guidelines for clinicians diagnosing diabetic foot infections. These guidelines were published in the October 1, 2004, issue of Clinical Infectious Diseases and infections were graded as follows:

Clinical Description Degree of Infection
No purulence or evidence of inflammation Uninfected
2 signs of inflammation, such as pain or induration; cellulitis, 2 cm or less around ulcer; infection limited to skin and subcutaneous tissues Mild
At least one of the following: cellulitis > 2 cm around ulcer, lymphangitis, spread beneath fascia, abscess, gangrene, or involvement of muscle, tendon, or bone Moderate
Evidence of local infection as well as systemic toxicity, such as fever, hypotension, leukocytosis, or azotemia Severe

The current prospective study applied these criteria to diabetic patients and followed them up for outcomes related to foot infections. The results of a study reported in the February issue of Clinical Infectious Diseases provides validation for their system.

Clin Infect Dis. 2007;44:562-565.