CODIFI (Concordance in Diabetic Foot Ulcer Infection): a cross-sectional study of wound swab versus tissue sampling in infected diabetic foot ulcers in England

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: Multi-centre, 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: Co-primary: 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; and, 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 method in 58% of patients, with more pathogens and fewer contaminants reported from tissues. The majority of pathogens were reported significantly more frequently in tissue than wound swab samples (p