Detection and Species Distribution of Fungal Pathogens Associated with Otomycosis in a Tertiary Health Center in Kano, Nigeria ^†

Abstract

Otomycosis is the commonest cause of otitis externa seen in otorhinolaryngology clinics, especially in tropical and subtropical regions of the world. Diagnosis is usually made clinically and confirmed by laboratory identification of fungal elements. We conducted a cross-sectional and hospital-based epidemiological study that aimed to determine the prevalence, distribution and antifungal susceptibility profile of common aetiologic agents of otomycosis in Kano, northwestern Nigeria. We collected clinical samples from 300 patients who presented with symptoms of external ear infection, out of which 117 subjects (39.0%) were mycologically positive. Aspergillus species were the predominant isolate, with 90 (77.0%), followed by Candida species at 27 (23.0%). Otomycosis accounts for 39% of otitis externa seen in our center, mostly presenting with pruritus and otalgia. Raising the awareness of the general population to the predisposing factors may significantly reduce the incidence of otomycosis.

1. Introduction

Otitis externa is estimated to account for 5–20% of all ear-related visits to Ear, Nose, and Throat (ENT) clinics, of which 10–25% have been attributed to otomycosis—a superficial fungal infection of the ear, involving the external auditory canal (EAC), auricle and even tympanic membrane. It usually manifests as pruritus, aural fullness, otalgia, otorrhea, and varied levels of hearing loss [1,2,3]. The infection is commonly unilateral, with the bilateral form being observed frequently among immunocompromised patients [4]. Diagnosis of otomycosis is challenging as it frequently relies on the patient’s history of exposure to risk factors, otoscopic examination and certain clinical presentations [5]. The current study aimed to evaluate the frequency and distribution of fungal pathogens associated with otomycosis among patients attending ENT clinics in a tertiary health center in Kano, Nigeria.

2. Materials and Methods

This was a prospective study conducted in the Department of Medical Microbiology and Parasitology, Bayero University Kano, Nigeria, from January to June 2024. A total of 300 patients with a clinical diagnosis of otitis externa were enrolled from the otorhinolaryngology clinic, ENT Department of Aminu Kano Teaching Hospital. Ethical approval was obtained from the research ethical committee of Aminu Kano Teaching Hospital, Kano (NHREC/28/01/2020/AKTH/EC/3748). Consent or assent was also obtained from the study participants before commencement of the research.

Two swab samples were taken from the EAC of each case. The first swab was evaluated for microscopy using potassium hydroxide (KOH) mount and Gram staining. The second swab was subjected to fungal culture on Sarbouraud’s dextrose agar with chloramphenicol at 25 °C and 37 °C. Isolates were identified using conventional mycological examinations. In addition, isolates with atypical morphology were identified to species level by PCR sequencing of the ribosomal DNA (rDNA) internal transcribed spacer (ITS). For yeast isolates, yeast-specific universal primers ITS1 (5′-TCC GTA GGT GAA CCT GCG G-3′) and ITS4 (5′-TCC TCC GCT TAT TGA TAT GC-3′) were used [3], and for Aspergillus species, the β-tubulin gene was amplified and sequenced using the primers Bt2a (5′-GGT AAC CAA ATC GGT GCT GCT TTC-3′) and Bt2b (5′-ACC CTC AGT GTA GTG ACC CTT GGC-3′) [6].

3. Results

Out of 300 patients, 117 subjects (39.0%) were mycologically positive; the rest were negative. Females 207 (69.0%) and individuals within the age group ≤ 10 years (44.3%) were the most affected. There is a statistically significant relationship between otomycosis and different age groups (p = 0.045). Most patients had unilateral presentation of otomycosis (285 (95.0%)), with predominant right ear infection in 215 (71.7%).

The table below (

Table 1. Results of direct microscopy (10% KOH) and culture.

Methods	Culture +ve (n, %)	Culture −ve (n, %)	Total (n, %)	p-Value
Direct microscopy +ve (n, %)	98 (32.7)	8 (2.7)	106 (35.3)	<0.001
Direct microscopy −ve (n, %)	19 (6.3)	175 (58.3)	194 (64.7)
Total (n, %)	117 (39.0)	183 (61.0)	300 (100)

KOH = Potassium hydroxide; +ve = positive; −ve = negative.

) shows a comparison of direct microscopy and culture results of the study participants. According to the findings, 35.3% of the samples were positive by direct microscopy and 39% were culture-positive. Interestingly, there was a statistically significant difference in the diagnostic yields between the two tests (p < 0.01).

The species distribution of the etiologic agents of otomycoses varied between yeast and mold. Whereas non-albicans candida was predominant in the yeast isolates, with Candida parapsilosis in the lead (Figure 1), Aspergillus species was the only mold isolated with a predominance of Aspergillus flavus. Sequences of those isolates identified using ITS PCR-sequencing were deposited into NCBI database, and their respective accession numbers are shown in

Table 2. Accession numbers of the isolates identified using ITS sequencing.

Yeast Strains	Accession No.	Mold Strains	Accession No.
Candida albicans	PX057625	Aspergillus flavus	PV999229
C. tropicalis	PX057626	A. fumigatus	PX057078
C. krusei	PX057628	A. terreus	PX057079
C. glabrata	PX056818	A. fumigatus	PX056813
C. parapsilosis	PX056819	A. niger	PX057422

.

4. Discussion

The occurrence of otomycosis varies with geographic location and is primarily influenced by environmental conditions. It is more prevalent in the tropics and seen in all ages. In this study, otomycosis accounted for 39.0% of otitis externa seen in our centers, which was comparable to the finding highlighted by earlier studies. The prevalence is similar to the 39.6% obtained in a study conducted in Ibadan, Western Nigeria [7], but lower than the 78.4% reported from in Lagos [5], that lies within the same western region.

Unilateral involvement was seen in 95% in our study, which correlates with another study in India, reported by Aggarwal and Jaiswal (2019), in which unilateral involvement was 92% [8]. Similarly, a study undertaken in Ekiti, Nigeria [1], reported unilateral ear infection in 95% of the subjects examined.

The current study revealed that the majority (44.3%) of the patients affected belonged to the age group of 0 and 10 years, followed by those in the age bracket 11 to 20 years, amounting to 24.0%. This is consistent with the age groups observed by other researchers from Sokoto, northern Nigeria [9], and Lagos, south-western Nigeria [5]. Similarly, in western Nigeria, Onotai and Osuji (2016) recorded a peak prevalence (30.7%) in the age groups of 1–10 years [10]. The predominance of this pediatric age with otomycosis could be a result of spending more time outdoors and being more exposed to fungal spores. On the other hand, other studies revealed a predominance of patients with otomycosis among young females of ages 12–30 years [11], 11–20 years [12] and 21–30 years [13]. Thus, otomycosis is a disease of all ages. In our study, there was a statistically significant difference between age group and otomycosis.

The current study revealed that Aspergillus was the most commonly isolated species (77%), followed by Candida (23%). Previous studies observed the same pattern [11,13]. The predominant Aspergillus spp. was Aspergillus flavus, which accounted for 34.2%, followed by Aspergillus niger 19.7%. This is in tandem with previous reports in which Aspergillus flavus predominates [5], but in disagreement to other studies [11,12,13,14] that reported Aspergillus niger as the predominantly isolated pathogen. The predominant Candida species was Candida parapsilosis, which correlates with a study conducted in Indonesia [15]. A more recent systematic review reported Aspergillus niger and Candida parapsilosis as the leading etiologies of otomycosis [16].

5. Conclusions

Otomycosis accounts for 39% of otitis externa seen in our center, mostly presenting with pruritus and otalgia. The spectrum of fungal pathogens isolated includes Aspergillus and Candida species. Aspergillus flavus and Candida parapsilosis were the most common etiologic agents isolated. Raising awareness among the general population to the predisposing factors may significantly reduce the incidence of otomycosis.