Diagnostic accuracy of eosinophil‐to‐lymphocyte ratio and eosinophil‐to‐neutrophil ratio as biomarkers for differentiating between fungal and bacterial infection in necrotising otitis externa

Abstract Introduction Necrotizing otitis externa (NOE) is a serious, progressive, and potentially life‐threatening infection of the external auditory canal, affecting soft tissue and bone. The most common organism causing NOE is Pseudomonas Aeruginosa and less common are Fungal infections. When managing a patient with NOE, a culture is taken from the EAC in order to tailor the appropriate antimicrobial treatment, however commonly, the culture is sterile. Inflammation biomarkers may be used as adjuncts to inform on the differential diagnosis and as prognostic markers. Aim To characterize and compare values and ratios of components of the complete blood count (CBC) at admission, at patients with positive swab culture. Methods A retrospective study of NOE patients was conducted. We included all patients admitted between the years 2001‐2023, for whom a culture swab tested positive. We compared CBC findings at hospitalization between bacteria and fungi‐positive culture patients. Results Eosinophils‐to‐Neutrophils Ratio (ENR) was significantly lower in the fungal group compared to the bacterial group 0.023 ± 0.02 and 0.04 ± 0.03, respectively ( p ‐value = 0.025). Eosinophils‐to‐Leukocyte Ratio (ELR) was significantly lower in the fungal group compared to the bacterial group 0.058 ± 0.04 and 0.12 ± 0.1 respectively ( p ‐value = 0.009). For definition of ELR ≤ 0.1 we found that, sensitivity was 88% (95%CI = 0.679‐0.979) and NPV 90% (95%CI = 0.709‐0.982). For definition of ENR ≤ 0.03 sensitivity was 88% (95%CI = 0.679‐0.979) and NPV 88% (95%CI = 0.679‐0.979). Conclusion Lower values of ELR and ENR in patients with NOE are associated with fungal infection and can serve as a tool in adjusting an appropriate antimicrobial therapy in cases of sterile or when no culture is available.