Prevalence and Microbial Association of Onychomycosis in Patients with Diabetic Foot Ulcers: A Retrospective Observational Study

Background: Onychomycosis is a common fungal nail infection among individuals with diabetes mellitus and may contribute to diabetic foot complications by altering the local microbial environment and increasing the risk of secondary bacterial infection. This study aimed to determine the prevalence of onychomycosis and evaluate its association with clinical and microbiological characteristics among patients with diabetic foot ulcers. Methodology: This retrospective observational study included 226 adult patients with diabetic foot ulcers treated at a tertiary referral center in South Kerala, India. Clinical records were reviewed to obtain demographic, clinical, and microbiological data. Onychomycosis was diagnosed based on compatible clinical findings with microbiological confirmation using potassium hydroxide microscopy and/or fungal culture. Categorical variables were summarized using frequencies and percentages. Univariate binary logistic regression was performed to identify factors associated with onychomycosis. Results: Of the 226 patients included in the study, 85 (37.6%) had confirmed onychomycosis. Among patients with onychomycosis, 35 (41.2%) were aged 61-70 years, 54 (63.5%) were male, and 60 (70.6%) had diabetes duration >10 years. Poor glycemic control (HbA1c >9%) was observed in 43 (50.6%) patients, while peripheral neuropathy was present in 73 (85.9%). Polymicrobial ulcer cultures were identified in 44 (51.8%) patients with onychomycosis. Gram-negative bacilli were isolated in 49 (57.6%) patients, Pseudomonas aeruginosa in 30 (35.3%), and osteomyelitis was present in 35 (41.2%). On univariate binary logistic regression analysis, diabetes duration >10 years (OR: 2.30, 95% CI: 1.24-4.28; p=0.008), peripheral neuropathy (OR: 2.67, 95% CI: 1.33-5.34; p=0.005), polymicrobial infection (OR: 2.26, 95% CI: 1.30-3.91; p=0.004), Pseudomonas aeruginosa isolation (OR: 2.10, 95% CI: 1.14-3.86; p=0.017), and osteomyelitis (OR: 2.38, 95% CI: 1.33-4.26; p=0.003) were significantly associated with onychomycosis. Conclusions: More than one-third of patients with diabetic foot ulcers had concomitant onychomycosis. Longer duration of diabetes, peripheral neuropathy, polymicrobial infection, Pseudomonas aeruginosa isolation, and osteomyelitis were significantly associated with onychomycosis. Routine nail examination and timely identification of fungal nail infection may complement comprehensive diabetic foot assessment and help identify patients at increased risk of complicated foot infections.