• Andrea Nelson, Alexandra Wright-Hughes, Michael Ross Backhouse, Benjamin A Lipsky, Jane Nixon, Moninder S Bhogal, Catherine Reynolds, Sarah Brown, and CODIFI collaborators.
• School of Healthcare, University of Leeds, Leeds, UK.
• BMJ Open. 2018 Jan 31; 8 (1): e019437.

ObjectiveTo determine the extent of agreement and patterns of disagreement between wound swab and tissue samples in patients with an infected diabetic foot ulcer (DFU).DesignMulticentre, prospective, cross-sectional study.SettingPrimary and secondary care foot ulcer/diabetic outpatient clinics and hospital wards across England.ParticipantsInclusion criteria: consenting patients aged ≥18 years; diabetes mellitus; suspected infected DFU.Exclusion Criteriaclinically inappropriate to take either sample.InterventionsWound swab obtained using Levine's technique; tissue samples collected using a sterile dermal curette or scalpel.Outcome MeasuresCoprimary: reported presence, and number, of pathogens per sample; prevalence of resistance to antimicrobials among likely pathogens. Secondary: recommended change in antibiotic therapy based on blinded clinical review; adverse events; sampling costs.Results400 consenting patients (79% male) from 25 centres.Most prevalent reported pathogens were Staphylococcus aureus (43.8%), Streptococcus (16.7%) and other aerobic Gram-positive cocci (70.6%). At least one potential pathogen was reported from 70.1% of wound swab and 86.1% of tissue samples. Pathogen results differed between sampling methods in 58% of patients, with more pathogens and fewer contaminants reported from tissue specimens.The majority of pathogens were reported significantly more frequently in tissue than wound swab samples (P<0.01), with equal disagreement for S. aureus and Pseudomonas aeruginosa. Blinded clinicians more often recommended a change in antibiotic regimen based on tissue compared with wound swab results (increase of 8.9%, 95% CI 2.65% to 15.3%). Ulcer pain and bleeding occurred more often after tissue collection versus wound swabs (pain: 9.3%, 1.3%; bleeding: 6.8%, 1.5%, respectively).ConclusionReports of tissue samples more frequently identified pathogens, and less frequently identified non-pathogens compared with wound swab samples. Blinded clinicians more often recommended changes in antibiotic therapy based on tissue compared with wound swab specimens. Further research is needed to determine the effect of the additional information provided by tissue samples.Trial Registration NumberISRCTN52608451.© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

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