How reliable are cultures of specimens from superficial swabs compared with those of deep tissue in patients with diabetic foot ulcers?

Purpose: To assess the reliability of cultures of superficial swabs (SS) by comparing them with cultures of concomitantly obtained deep tissue (DT) specimens in patients with diabetic foot ulcers. Methods: We reviewed clinical and microbiological data from patients with diabetes who presented during a two-year period to our hyperbaric medicine center with a foot ulcer. We identified patients who had at least one concomitantly collected SS and DT pair of specimens sent for culture. Results: A total of 89 culture pairs were available from 54 eligible patients, 33 (61.1%) of whom were hospitalized. Wounds were infected in 47 (87.0%) of the patients and 28 (51.9%) patients had received antibiotic therapy within the previous month. Overall, 65(73%) of the SS and DT pairs had identical culture results, but in 11(16.9%) cases the cultures were sterile; thus, only 54 (69.2%) of the 78 culture-positive pairs had identical results. Compared with DT, SS cultures yielded >= 1 extra organism in 10 (11.2%) cases, missed at least one organism in 8 (9.0%), and were completely different in 6 (6.7%). When compared to DT culture results, SS cultures had a positive predictive value of 84.4%, negative predictive value of 44.0%, and overall accuracy of 73.0%. Conclusions: In patients with diabetic foot ulcers, results of specimens for culture taken by SS did not correlate well with those obtained by DT. This suggests that SS specimens may be less reliable for guiding antimicrobial therapy than DT specimens. (c) 2012 Elsevier Inc. All rights reserved.