From the Guidelines
The best way to differentiate between fungal and bacterial otitis externa is through clinical examination and microscopic evaluation of ear canal debris, with fungal infections typically presenting with thick, white or colored debris and intense itching, while bacterial infections present with more severe pain, erythema, and purulent discharge 1.
Key Differentiating Features
- Fungal otitis externa:
- Thick, white or colored debris (often described as "wet newspaper" appearance)
- Minimal pain
- Intense itching
- Microscopic examination showing fungal elements like hyphae or spores is diagnostic
- Bacterial otitis externa:
- More severe pain
- Erythema
- Edema
- Purulent discharge
- Significant tenderness when moving the tragus or pinna (positive "tragal sign")
- Otoscopic examination may reveal granulation tissue
Diagnostic Approach
If microscopy is unavailable, response to therapy can be diagnostic - fungal infections won't respond to antibacterial treatments alone 1.
Treatment
For suspected fungal infections, treatment includes thorough cleaning of the ear canal and antifungal drops like clotrimazole 1% solution twice daily for 7-10 days 1. For bacterial infections, antibiotic drops containing fluoroquinolones (ciprofloxacin 0.3%) or combination products with steroids are typically effective 1. The distinction matters because inappropriate treatment can worsen symptoms and lead to complications like hearing loss or spread of infection to surrounding tissues.
Special Considerations
Patients with diabetes, an immunocompromised state, or both require special consideration because they are susceptible to otomycosis and necrotizing otitis externa, which may present similar to AOE but require different management 1. In these cases, it is essential to consider the possibility of fungal or necrotizing otitis externa and adjust the treatment approach accordingly.
From the Research
Differentiating between Fungal and Bacterial Otitis Externa
To differentiate between fungal and bacterial otitis externa, several methods can be employed:
- Direct preparation of specimens: Using optical brighteners, mycologic culture, and histologic examination is strongly recommended for the correct diagnosis 2.
- Imaging studies: Along with the patient's history and otoscopic examination under microscopic control, imaging studies can aid in diagnosis 2.
- Eosinophil-to-lymphocyte ratio (ELR) and eosinophil-to-neutrophil ratio (ENR): Lower values of ELR and ENR are associated with fungal infection and can serve as a tool in adjusting appropriate antimicrobial therapy in cases of sterile or when no culture is available 3.
- Culture swab: Taking a culture swab from the external auditory canal can help identify the causative organism, although it is commonly sterile 3.
Diagnostic Markers
Some diagnostic markers that can help differentiate between fungal and bacterial otitis externa include:
- ELR: An ELR of ≤0.1 has a sensitivity of 88% and a negative predictive value (NPV) of 90% for fungal infection 3.
- ENR: An ENR of ≤0.03 has a sensitivity of 88% and an NPV of 88% for fungal infection 3.
Treatment
Treatment for otitis externa depends on the causative organism:
- Fungal otitis externa: Topical antifungals, such as clotrimazole, miconazole, bifonazole, ciclopiroxolamine, and tolnaftate, are potentially safe choices for treatment 2.
- Bacterial otitis externa: Topical antibiotics, such as ciprofloxacin, can be effective in treating bacterial otitis externa 4, 5.
- Non-antibiotic treatments: Antiseptics, steroids, and non-phancerals can be effective in treating acute otitis externa, with no significant difference in cure rates compared to topical antibiotics 6.