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Researchers push for revision of IDSA diabetic foot infection classification
Researchers suggested that diabetic foot osteomyelitis — which results in worse outcomes compared with soft tissue infections — should be separated into its own category in the Infectious Diseases Society of America’s diabetic foot classification system to better guide treatment and improve outcomes.
“We need to base classification systems on evidence and not intuition,” Lawrence A. Lavery, DPM, MPH, podiatrist and professor of plastic surgery, orthopedic surgery and physical medicine and rehabilitation at the University of Texas Southwestern Medical Center, told Infectious Disease News.
The current severe infection identification system is based on systemic inflammatory response syndrome (SIRS) criteria, which do not suitably define moderate and severe infections, Lavery explained. He said this is because SIRS criteria “[do] not impact hospital treatments or complications and treatments after the index hospitalization.”
“Patients with osteomyelitis have more complicated hospital experiences and more complications during the year following discharge after their index hospitalization. The IDSA has recommendations for the duration of antibiotic therapy based on the presence of osteomyelitis and if the infected bone is completely resected, partially resected, if necrotic bone is left or if there is no surgery,” Lavery said. “However, the classification system has not included a treatment tier that reflected the importance of osteomyelitis.”
Lavery and colleagues conducted a retrospective cohort study that included 294 patients with moderate and severe diabetic foot infections. Diabetic foot osteomyelitis was confirmed via bone culture or histopathology, whereas soft tissue infections were based on negative bone culture, MRI or single photon emission CT, the researchers explained.
They reported that patients with osteomyelitis had worse outcomes than patients with soft tissue infections. Specifically, 99.4% of patients with osteomyelitis required surgery, 83.4% required amputation, 56.7% became reinfected and 49.7% experience acute kidney injury. Comparatively, 55.5% of patients with soft tissue infection required surgery, 26.3% required amputation, 38% became reinfected and 37.2% experienced acute kidney injury. Moreover, those with osteomyelitis experienced longer antibiotic duration (32.5+/-46.8 vs. 63.8+/-55.1 days, P < .01) and length of stay (14.5+/-14.9 vs. 22.6+/-19.0 days, P < .01), and required more surgeries compared with patients with soft tissue infections (2.1+/-1.3 vs. 3.3+/-2.3, P < .01).
When Lavery and colleagues compared moderate and severe soft tissue infections, they found differences only for infection readmission, with readmittance occurring for 46.2% of moderate infections and 25% of severe infections, and acute kidney injury (31.2% vs. 50%).
When comparing moderate and severe osteomyelitis, the researchers noted differences in the number of surgeries (2.8+/-2.1 vs. 4.1+/-2.5, P < .01) and length of stay (18.6+/-17.5 vs 28.2+/-17.7, P < .01).
“We believe there is a need to stratify infection severity, but SIRS criteria [do] not seem to work,” Lavery said. “The presence of abscess, depth and extent of abscess are criteria we are evaluating. Osteomyelitis without soft tissue abscess or localized abscess (as opposed to abscess in multiple compartments) probably [does] not require surgery or amputation as often or have prolonged antibiotics experience during the index amputation as more extensive abscesses.” – by Marley Ghizzone
Disclosures: The authors report no relevant financial disclosures.
Perspective
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The study by Lavery and colleagues addresses an important issue about, and offers some new data on, classifying diabetic foot infections (DFIs). I think it is necessary first to understand the aims of the IDSA (and International Working Group on the Diabetic Foot [IWGDF]) DFI classification scheme: 1) to define infection (and distinguish it from uninfected wounds); 2) to assess the severity of the infection with the goal of deciding which patients need more urgent care (eg, hospitalization, immediate diagnostic studies or surgical intervention); 3) to give guidance on antimicrobial treatment (eg, spectrum, route and duration of antibiotic therapy). Since its introduction in the guidelines published by both the IDSA and IWGDF in 2004, the scheme has been validated not only in the two studies cited in the Lavery paper but in at least four additional papers. In patients presenting with a DFI, these studies have overall shown that the scheme helps predict the likelihood of hospitalization, surgical intervention, lower extremity amputation, wound healing and length of hospital stay.
The IDSA DFI guidelines were last updated in 2012, but the IWGDF updated its DFI guidelines in 2015 and 2019 (https://iwgdfguidelines.org/infection-guideline). In preparing those updates, the working group discussed whether or not we should change any aspects of the infection classification scheme, and in 2019, we decided to adopt one of the two main suggestions promoted by Lavery and colleagues: We now denote the presence of osteomyelitis as a separate category (with the addition of [O]) for grade 3 (moderate) or grade 4 (severe) infections. After reviewing the two available articles, the working group agreed that the distinction of grade 3 and grade 4 infections was valid and useful, and that the SIRS criteria (while suboptimal) were still the best available means to distinguish these two.
The IDSA moderate grade infection is quite broad while including patients with serious deep infections, it can also include those with as little as 2 cm or more of cellulitis around a superficial ulcer, or extension of the infection to just below the subcutaneous tissue. As the authors of the Lavery study state, their population was exclusively composed of patients who were hospitalized (not outpatients) and from a “safety net hospital.” Thus, it is likely that even those classified as “moderate” had a serious infection, thereby potentially obscuring the differentiation from “severe.” Of note is that even in that population, all of the usual indicators of more serious infection are (presumably nonstatistically significantly) higher in the severe than the moderate infections; similarly, for both soft tissue and bone infections patients with severe (compared with moderate) infections had significantly worse outcomes in several categories.
Thus, I agree that specifically denoting the presence of osteomyelitis in patients presenting with a DFI is diagnostically and therapeutically useful for clinicians treating these patients, which we have now done in the 2019 IWGDF guidelines. I do not, however, believe we should stop distinguishing moderate from severe infections, because making this distinction in most populations (especially those presenting in outpatient clinics) helps to define the type and urgency of the next steps in managing DFIs.
The IDSA contacts the chairs of each of its guideline committees annually to ask if their guideline should be updated. I have informed IDSA that I think the 2012 version of the IDSA guidelines are due for an update, and my understanding is that they are on the list for update.