Tissue and Swab Culture in Diabetic Foot Infections

Abstract

We evaluated the diagnostic performance of swabs versus tissue cultures in 28 diabetic patients with neuropathic (group A) and 22 diabetic patients with neuroischemic foot ulcer (group B) and the differences in bacterial isolates between the 2 groups. In group A, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of swab cultures for the diagnosis of infection were 100%, 40%, 88.5%, and 100%, respectively. In group B, the corresponding values were 100%, 22.2%, 65%, and 100%. In group A, sensitivity, specificity, PPV, and NPV of swab cultures for the identification of pathogens were 100%, 14.3%, 53.8%, and 100%, respectively. In group B, the corresponding values were 100%, 18.2%, 55%, and 100%. In each group, Staphylococcus aureus and Pseudomonas aeruginosa were the most common isolates. The number of isolates was significantly higher on swab versus tissue cultures only in group A (P = .033). No differences were observed between groups in number of isolates and colony forming units. In conclusion, swab cultures are highly sensitive but less specific and have an excellent NPV both in diabetic patients with neuropathic and in those with neuroischemic foot ulcer. There are no differences between the groups in microbial load.

Concordance in diabetic foot ulceration: a cross-sectional study of agreement between wound swabbing and tissue sampling in infected ulcers

“…Two studies 62,63 have been published since the IDSA, NICE and IWGDF guidelines. Mutluoglu et al 62 assessed the reliability of cultures of superficial swabs by comparing them with cultures of concomitantly obtained deep tissue specimens in patients with DFUs.…”

“…Demetriou et al 63 assessed the diagnostic performance of swabs versus tissue cultures in 50 consecutive diabetic patients with a foot ulcer, 28 of which were neuropathic and 22 of which were neuroischaemic. The authors stated that 36 (72%) wounds were infected, based on 'the presence of at least 2 of the following criteria: local swelling or induration, erythema greater than 0.5 cm in any direction around the ulcer, local tenderness or pain, local increase of temperature, and purulent discharge'.…”

“…In keeping with our study, 52% of their patients had received antibiotic therapy at presentation. In a study of 50 patients with an infected DFU (who had not recently received antibiotic therapy), Demetriou et al 63 used a tissue specimen culture against which to compare a swab specimen culture. The results obtained from tissue cultures were the same as those obtained by swab in only 50% of patients.…”

“…Currently available evidence from the main diabetic foot infection guidelines (NICE, 37 IDSA 1,2,36 and the IWGDF 42,56 ) and other studies 62,63 is not sufficiently robust to advise clinicians on the best technique to identify pathogens in DFUs.…”

Advances in Infections and Wound Healing for the Diabetic Foot

“…All subjects presented with clinically infected foot ulcers. 7 It was found that swabs yielded excellent sensitivity (100%) and negative predictive value (100%), both for confirmation of infection and for identification of true pathogens, whereas their corresponding specificities (14% to 40%) and positive predictive values (54% to 88.5%) were less satisfactory. Thus, negative swab cultures emerged as very reliable in ruling out infection, and similarly, the absence of a microorganism could virtually exclude its role as a pathogen.…”