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Abstract
Objective To determine the extent of agreement and patterns of disagreement between wound swab and tissue samples in patients with an infected diabetic foot ulcer (DFU).
Design Multicentre, prospective, cross-sectional study.
Setting Primary and secondary care foot ulcer/diabetic outpatient clinics and hospital wards across England.
Participants Inclusion criteria: consenting patients aged ≥18 years; diabetes mellitus; suspected infected DFU. Exclusion criteria: clinically inappropriate to take either sample.
Interventions Wound swab obtained using Levine’s technique; tissue samples collected using a sterile dermal curette or scalpel.
Outcome measures Coprimary: 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.
Results 400 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).
Conclusion Reports 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 number ISRCTN52608451.
- diabetic foot infection
- agreement
- wound swab sample
- tissue sample
- diabetic foot ulcers
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Footnotes
Contributors AN (Professor of Wound Healing) was the chief investigator of the study and is the guarantor. She initiated the study, led the grant application development and the study team, and was involved in drafting and revising the paper critically for intellectual content. AWH (Senior Statistician) was a member of the study team, contributed to the drafting of the statistical analysis plan, undertook the statistical analyses, drafted the statistical results and contributed to the drafting and revising of the paper for intellectual content. MRB (NIHR Research Fellow, Podiatrist) was the first clinical study coordinator, a member of the study team, initiated sites for recruitment, contributed to the drafting of the study report and revised the paper for intellectual content. BAL (Professor of Medicine) was a coapplicant on the study grant, a member of the study team, contributed to the drafting of the paper and revised the paper for intellectual content. JN (Professor of Tissue Viability) was a coapplicant on the study grant, a member of the study team, the lead for the Clinical Trials Unit activity and responsible for these aspects. She contributed to the drafting of the manuscript and reviewed it for intellectual content. MSB (Senior Trial Coordinator) was the trials unit study coordinator and a member of the study team. He was responsible for ethics and governance applications and coordinated the study team. He contributed to the drafting of the study report and revised the paper for intellectual content. CR (Senior Data Manager) was the data manager and a member of the study team, responsible for data quality, contributed to the drafting of the study report and revised the paper for intellectual content. SB (Principal Statistician) was the supervising statistician, a coapplicant on the study grant, a member of the study team, contributed to the drafting of the statistical analysis plan, oversaw the statistical analyses and preparation of the statistical results. She contributed to the drafting of the manuscript and reviewed the paper for intellectual content.
Funding This work was supported by the National Institute for Health Research (NIHR) Health Technology Assessment (HTA) programme (project number 09/75/01).
Disclaimer The views and opinions expressed herein are those of the authors and do not necessarily reflect those of the HTA programme, NIHR, NHS or the Department of Health.
Competing interests None declared.
Patient consent Obtained.
Ethics approval CODIFI received ethical approval from the Sheffield NRES Committee (Ref: 11/YH/0078) and each enrolling site obtained local ethical approval prior to commencing recruitment.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Requests for data should be made to the corresponding author.
Collaborators The CODIFI collaborators were A Nelson, J Nixon, S Brown, J Gray, J Firth, C Dowson, E Jude, T Dickie, C Amery, G Sykes, P Vowden and M Edmonds.