Comparison of microbiological results of needle puncture vs. superficial swab in infected diabetic foot ulcer with osteomyelitis

Aim To study prospectively two methods for the bacteriological diagnosis of osteomyelitis related to diabetic foot ulcer: needle puncture performed across normal skin surrounding the foot ulcer and superficial swabbing of the ulcer. Patients and methods Diabetic patients with a foot ulcer complicated by bone or joint infection, as detected by X-ray imaging, were included in the study. Ulcer swabbing and needle puncture were performed in each patient. To reach the tissue nearest the bone surface, needle puncture was guided by X-ray imaging and the drop of fluid obtained by aspiration was used for both aerobic and anaerobic bacterial culture. Results Twenty-one diabetic patients were included. The mean number of microorganisms isolated by needle puncture was significantly lower compared with that obtained by superficial swabbing: 1.09 vs. 2.04 (P < 0.02). Three bacterial species were isolated by needle puncture only in one patient while three or more bacterial isolates were obtained by superficial swabbing in six patients. No bacterial isolate was detected in five patients by needle puncture and in two patients by superficial swabbing. Staphylococcus aureus accounted for 70% of cases (seven patients) when a single bacterial species was obtained by needle puncture. After needle puncture, no wound complication or infection was observed. Conclusion Culture of samples obtained by needle puncture revealed one or two bacterial isolates in two-thirds of diabetic patients with osteomyelitis following foot ulcer. Given the lack of complications, this invasive diagnostic technique should be considered for deep direct sampling in diabetic patients with osteomyelitis related to foot ulcer when surgical debridement is contraindicated or delayed.