Developing diagnostic criteria to differentiate fungal foot infections caused by Neoscytalidium dimidiatum and dermatophytes

BACKGROUND: The predisposing factors and clinical presentations of fungal foot infections caused by non-dermatophytes and dermatophytes are challenging to differentiate. Definite diagnoses of non-dermatophyte infections at first visits facilitate their treatment. OBJECTIVES: This study aimed to develop diagnostic criteria to differentiate fungal foot infections caused by Neoscytalidium dimidiatum and dermatophytes. METHODS: Diagnostic prediction research based on a retrospective, observational, cross-sectional study. The reviewed patients were aged ≥18 and underwent a mycological examination for fungal foot infections. A fungal culture at the initial visit was the gold standard for determining causative organisms. RESULTS: Analyses were carried out on the data from 371 patients. N. dimidiatum accounted for 184 (49.6%) infections, and dermatophytes caused the remaining 187 (50.4%) cases. Five significant predefined predictors were used to develop the diagnostic criteria and score. They were immunocompetence status, no family history of fungal infections, the absence of pruritus, the absence of other concurrent fungal skin infections, and agricultural work. The lower score cutoff was <8 (sensitivity 97.8% and specificity 25.7%). The higher cutoff was >11 (sensitivity 83.7% and specificity 57.8%). The score showed an area under the receiver operating characteristic curve of 0.755 and was well calibrated. CONCLUSIONS: The criteria and score show promise for clinical use, with acceptable discriminative performance and good calibration. They will help physicians differentiate the causative organisms in patients with fungal foot infections at the first visit, enabling the determination of appropriate antifungal treatment.