Cultures of diabetic foot ulcers without clinical signs of infection do not predict outcomes.

Abstract

We examined associations between ulcer bioburden and ulcer outcomes in neuropathic diabetic foot ulcers (DFUs) that lacked clinical signs of infection. Three dimensions of bioburden (i.e., microbial load, microbial diversity, and the presence of likely pathogens) were measured at baseline using swab cultures obtained by Levine's technique. Subjects were assessed every 2 weeks for 26 weeks to determine the rate of healing and development of infection-related complications. Foot ulcers were off-loaded using total-contact casts and routinely debrided. To establish associations between bioburden and rate of healing, Cox proportional hazards and least squares regression were used after adjusting for ulcer depth, surface area, and duration. A total of 77 subjects completed the study. Sixty-five (84.4%) had ulcers that healed during follow-up; weeks-to-closure ranged from 2 to 26 (median 4.0). Mean (± SD) percent reduction in surface area/week was 25.0% (± 23.33). Five (6.5%) of the DFUs developed an infection-related complication. None of the bioburden dimensions (i.e., microbial load, microbial diversity, or presence of likely pathogens) was significantly associated with weeks-to-closure or percent reduction in surface area per week. Weeks-to-closure was best predicted by ulcer duration, depth, and surface area (c-statistic = 0.75). Culturing DFUs that showed no clinical signs of infection had no predictive value for outcomes of DFUs managed with total-contact casts and routine debridement. These findings support recommendations of the Infectious Disease Society of America that culturing and antibiotics should be avoided in treating DFUs that show no clinical signs of infection.