CHICAGO — Clinical symptoms are critical in distinguishing between uninfected and mildly infected diabetic foot lesions, Warren S. Joseph, D.P.M., reported at the Vascular Annual Meeting.
For instance, lack of cellulitis indicates lack of infection, as does good granulation. If the wound is purulent, it is infected.
Surprisingly, culturing the wound for microorganisms is not the best way to diagnose infection. This is because even noninfected diabetic foot lesions are “wound toilets” or, less bluntly, they have a significant “bioburden or bioload” of microorganisms that are simply colonizing the lesion, said Dr. Joseph of the Veterans Affairs Medical Center in Coatesville, Pa.
Just because an ulcer is colonized does not mean it is infected, he explained. However, in patients whose diabetic foot lesions are colonized but not infected, physicians may feel uncomfortable about doing nothing, Dr. Joseph said. They know the microbes are there, and they feel compelled to provide treatment, he said.
In this situation, topical treatments such as those with broad-spectrum activated silver are better than systemic antibiotics. And yet there is little evidence that topical antibiotics have any benefit for healing wounds, he said. In addition, they have little effect on preventing infection.
“Antibiotics do not heal wounds, antibiotics treat infection,” Dr. Joseph said, adding that he could not overemphasize the point that systemic antibiotics do not have a place in treating noninfected wounds.
Why? Because the first strain of vancomycin-resistant Staphylococcus aureus was found in a diabetic foot wound; it showed up in a swab culture of a clinically noninfected wound.
According to Dr. Joseph, the Infectious Diseases Society of America classification system developed last year defines mild infection as that extending less than 2 cm (www.idsociety.org
It is a misconception, Dr. Joseph pointed out, that all diabetic foot infections are polymicrobial. Virtually all diabetic foot infections have been shown to be caused by just two microorganism types—Staphylococcus aureus and group B streptococci. “This is great news, because when you think about what antibiotics you need for staph and strep—just about anything,” he said. “Those broad-spectrum drugs we have been using all these years we probably do not need, with one small caveat—there has been an incredible increase in prevalence of methicillin-resistant staph in [the] diabetic foot.” The bottom line is that 40% or more of all diabetic foot staph infections are methicillin resistant.
The number of diabetic foot patients who presented with methicillin-resistant Staphylococcus aureus doubled between 1999 and 2002, he said.
Given the variety of alternatives available—anything you would use for staph or strep throat—Dr. Joseph said: “Do not use ciprofloxacin in the infected diabetic foot.”
The reasoning is that it has poor activity against staph and strep, and it is a single-step mutation to getting staph or strep resistant to ciprofloxacin.
“You might have a nice big S sitting next to the cipro line, but give that patient the drug, [and] within a week it's going to turn to an R.”
Dr. Joseph said that he believes ultimately it will be shown that severe infections will respond to antibiotics directed against staph and strep, even if there are corresponding anaerobic microbes present.
He used the analogy of a snake: Remove the head (staph and strep), and the rest dies.
However, he stated that the clinical data are not there just yet to support advising against the use of broad-spectrum antibiotics for such infections, and so he could not recommend it.
Dr. Joseph disclosed financial relationships with Merck and Pfizer.