A new classification for moderate diabetic foot infection

An interesting open-access article has been published on classification of infections. Professor Lipsky and colleagues describe their dissatisfaction with different classification systems that have been proposed over the past few decades for skin and soft tissue infections (SSTI). They contrast the lack of validation of any of these to the several published studies that have suggested usefulness and validity of the diabetic foot infection (DFI) classification scheme proposed over a decade ago by the Infectious Diseases Society of America (IDSA) and the International Working Group on the Diabetic Foot. They suggest that with slight modifications of the IDSA classifications for SSTI and DFI, they could be harmonized into a clinically useful system. This results in an insightful article and propositions to change and align the various systems.

For those unfamiliar with the DFI classification scheme, it first defines infection (clinically, by the presence of at least two classical findings of inflammation) and categorizes infections as mild (limited and superficial), moderate (more extensive or deeper) and severe (accompanied by evidence of systemic infection). Since its proposal, the system has been widely used and been found to be useful for: predicting the need for and duration of hospitalization for DFI; the likelihood of a DFI patient undergoing a lower extremity amputation; the likelihood of other adverse outcomes; and, reducing cost of treatment. No such widely used or studied system is available for other types of SSTIs.

The new system the authors propose (with the complicated acronym COCLASSTI), brings most of the previously proposed classifications together. As part of this proposal, the new system dealt with one major limitation of the DFI classification, i.e., the fact that the largest and most heterogeneous group is “moderate” infections. Thus, the one change they suggested in the DFI classification is that moderate infections be separated into two groups. Moderate class A infections are defined as those with a wound surrounded by more than 2 cm of redness, and a horizontal distribution; moderate class B infections have a more vertical distribution, extending below the subcutaneous tissue. The one other addition of the new system is that it addresses the potential role of topical antimicrobial therapy, which they suggest is appropriate for some Class 1 (superficial, limited) SSTI and mild DFIs, and potentially useful as adjunctive to systemic antibiotic therapy for Class 2A (pyodermas) SSTIs and Moderate Class A DFIs.

This paper provides some historical and clinical discussion of classifications of SSTI and DFI, but no validation data. This will hopefully change in the near future, as existing databases might be well suited to attempt to validate the updated system directly. Furthermore, the authors call for comments and discussion, in the hope of continuing this interesting debate.

Is this change in classification important for tomorrow’s daily clinical practice? Even though you do not have to change your practice immediately, the answer is yes. We are all facing a major global crisis of antimicrobial resistance; anything we can do to improve antimicrobial stewardship will help this problem. When treatment for moderate class A infections is started using parenteral antibiotics, this should be rapidly switched to oral (preferably more narrowly targeted) antibiotics; such a rapid switch may be less appropriate for class B moderate infections. Furthermore, moderate class A infections are potentially amenable to topical therapy alone, which is not the case for moderate class B infections. So keep your eyes and ears open, and considering joining in, as this debate will lead to more stimulating papers and clinical changes in the near future.