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Otomycosis: a systematic review and meta-analysis of prevalence and causative agents in the era of molecular diagnostics

BMC Infectious Diseases volume 25, Article number: 544 (2025) Cite this article

Abstract

Background

Molecular identification of fungal agents in otomycosis can provide a more accurate diagnosis and differentiation of species compared to conventional morphological methods. Previous reviews mostly relied on studies using conventional methods to explore the prevalence and distribution of otomycosis etiologies. We aim to estimate the prevalence and distribution of causative agents in otomycosis cases confirmed with molecular methods.

Methods

We conducted a systematic search of PubMed, Scopus, Web of Science, and Google Scholar. We selected cross-sectional studies that reported causative agents of otomycosis and used molecular methods for identification of fungi. We appraised the quality of evidence using the JBI Checklist for Prevalence Studies. Clinical and mycological data were collected, and prevalence of otomycosis was estimated by meta-analysis.

Results

Twenty studies reporting 1392 fungal isolates, consisting of 46 species from 11 distinct genera, were included in this review. The prevalence of otomycosis among clinically-suspected patients was 58.3% (95% CI: 41.4–73.5%). Aspergillus (75.8%, 95% CI: 70.3–80.6%) and Candida (15.3%, 95% CI: 8.7– 25.6%) were the most common etiologies. The most frequent Aspergillus species were A. niger (n = 352, 30.9%) and A. tubingensis (n = 270, 23.7%), and the most frequent Candida species were C. parapsilosis (n = 85, 39.7%) and C. albicans (n = 66, 30.8%). The quality of evidence was assessed to be poor in all included studies.

Conclusions

Otomycosis is caused by a diverse set of species, predominantly from Aspergillus and Candida genera. Molecular identification techniques provide a more accurate understanding of the distribution of species associated with otomycosis.

Clinical trial number

Not applicable.

Peer Review reports

Background

The external auditory canal (EAC) is often colonized by fungi since it provides the organisms with essential nutrients, such as carbohydrates and amino acids, as well as optimal temperature, moisture, and pH [1]. The fungi may occasionally cause superficial mycotic infections of the EAC, known as fungal otitis externa or otomycosis, which can present as an acute, subacute, or chronic disease [2]. Otomycosis is responsible for 9 to 30% of the external otitis cases, and it is widespread around the world, with cases having been reported from Africa, Asia, Europe, and America [3].

Otomycosis can be associated with complications, including tympanic membrane perforation, involvement of the middle ear, serous otitis media, recurrent infections, and invasion to adjacent bones. These complications may require intensive treatment and follow-up [4,5,6]. Furthermore, fungal infections account for 12 to 35% of necrotizing or malignant otitis externa, a severe fatal disease often seen in immunosuppressed patients [7, 8]. In addition, an increase in emerging antifungal-resistant pathogens, such as Candida auris, introduces new challenges to the treatment of this infection [9].

Otomycosis is often diagnosed clinically based on the history and examination of EAC, revealing accumulation of whitish or blackish debris, discharge, or erythema [10]. However, the clinical presentations of otomycosis can be indistinguishable from the bacterial otitis externa, and paraclinical methods should be used to confirm the diagnosis [11]. In addition, conventional laboratory methods, such as microscopic examination and cultivation, are limited in their sensitivity and specificity for detecting the fungal agents and can be time-consuming [12].

Molecular diagnostic methods may overcome these limitations and provide a better knowledge of the variety of fungi causing otomycosis, as these methods can detect species undetectable with conventional methods [13]. Particularly, DNA sequencing, especially using the internal transcribed spacer (ITS) region, is considered the gold standard of fungal identification and has been useful for detection of otomycosis agents [14, 15]. Furthermore, a multiplex polymerase chain reaction (PCR) assay has been shown to be more sensitive and less time-consuming than culture in identifying fungi in cerumen samples [16].

Previous reviews on the prevalence and distribution of otomycosis causative agents have largely relied on conventional diagnostic methods, i.e. morphological examination [17, 18]. To the best of our knowledge, no previous review specifically described otomycosis on the basis of molecular methods of detecting fungal agents. In this systematic review, we aim to estimate the prevalence of otomycosis cases confirmed with molecular methods in patients with signs and symptoms of external otitis. We also intend to understand the distribution of causative agents of otomycosis detected through molecular investigations.

Methods

This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Additional File 1) [19] and its protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO registration code: CRD42022380730). The eligibility criteria for inclusion in the review were reporting data on patients with otomycosis, fungal agents detected using molecular diagnostic tools (i.e., PCR-based methods), cross-sectional study design, and being written in English. Editorials, reviews, case reports, and articles on otomycosis lacking a molecular identification of the causative agents were excluded. Case series with less than ten patients were also excluded, unless the study only included a specific genus of fungi.

We searched PubMed, Scopus, Web of Science, and Google scholar up to April 10, 2023. A combination of keywords “otomycosis”, “fungal otitis”, “fungal ear infection”, and the MeSH term “otomycosis” was used to search the titles and abstracts of documents. We restricted the results to English language only. We did not limit our search based on publication date or format. Two independent reviewers screened the documents based on the titles and abstracts after omitting the duplicates. Two authors independently reviewed the remaining articles and selected those meeting the eligibility criteria. Any disagreement between the reviewers was resolved by discussing with a third person.

The quality of evidence was critically evaluated by two independent reviewers using the Joanna Briggs Institute (JBI) Critical Appraisal Checklist for Studies Reporting Prevalence Data [20]. This checklist consists of nine items that assess various aspects of a study, including the appropriateness of the sample frame, the sampling method and sample size adequacy, the thoroughness of subjects’ description, the sufficiency of response rate and coverage, the validity and reliability of measurements, and the suitability of statistical analysis. We planned to conduct a sensitivity study based on the level of quality.

Data extracted from eligible articles included the first author, publication year, study location, participant or sample inclusion criteria, total number of participants, number of diagnosed otomycosis cases, age, sex, clinical presentations, risk factors, affected ear, number of fungal isolates, diagnostic methods, and fungal genera and species identified by molecular methods. An author extracted the data, and a second author verified them. A third reviewer was discussed in case of discrepancies.

Meta-analysis was performed to estimate the pooled prevalence of otomycosis, causative agents, clinical presentations, and risk factors, using R packages metafor and meta [21, 22]. Heterogeneity was assessed with the I2 statistic. A random-effects model was used in cases of significant heterogeneity (I2 > 50%). Otherwise, we would have used a fixed-effect model. The pooled value and 95% confidence interval (CI) of prevalence are reported, and the results are demonstrated in forest plots. We intended to perform subgroup analyses based on geographical area and methods of diagnosis if there were at least 10 studies in a meta-analysis with I2 > 50%. We planned to assess publication bias through a funnel plot asymmetry test if there were at least 10 studies in the meta-analyses.

Results

A total of 1216 documents were retrieved from searching the databases, and 315 were read for eligibility criteria. Finally, 20 cross-sectional studies [13, 23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41] were eligible for inclusion in our review (Fig. 1). Eight studies included patients with clinical presentations of otitis externa. Twelve studies investigated fungal strains of specific genera isolated from otomycosis cases, including Aspergillus species (n = 4), Aspergillus section Nigri (n = 7), and Candida species (n = 1). Table 1 summarizes the characteristics of the included studies.

Fig. 1
figure 1

PRISMA flow diagram of search for studies on otomycosis with molecular identification of causative agents

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Table 1 Characteristics of included studies
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All reports were assessed as having a poor quality of evidence based on the JBI Critical Appraisal Checklist, getting between 3 and 5 out of 9 points. The results of the assessments are presented in Additional File 2. Most studies lacked an appropriate sample frame as they only included patients from a specific clinic or hospital department or failed to clarify their sample frame. None of the reports clearly explained the sampling method, and only two recruited a large enough sample. Furthermore, no study reported any information on the response rates or whether different subgroups had different response rates. However, all studies used valid and reliable methods for confirming the diagnoses.

Seven out of eight studies including patients with clinical suspicion of fungal otitis provided data on the total number of suspected patients and those confirmed with otomycosis. In these seven studies, the diagnosis of otomycosis was confirmed in 918 patients using a molecular method (Table 2). One study reported only the number of isolates collected and did not report the number and clinical characteristics of patients and was, therefore, not included in meta-analyses [24]. We performed meta-analyses, using random-effect model, for variables reported in at least six studies.

Table 2 Demographic and clinical features of studies including patients with clinical presentations of otomycosis
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Otomycosis was slightly more prevalent in women (53.4%, 95% CI: 46.3–60.3%, I2 = 77.7%). Bilateral ear involvement was reported in 6.1% of cases (95% CI: 2.0–17.1%, I2 = 89.2%). The most commonly reported clinical presentations of otomycosis were pruritus (75.1%, 95% CI: 64.7–83.3%, I2 = 91.8%) and otalgia (65.2%, 95% CI: 58.5–71.3%, I2 = 75.3%). Manipulation of ear canal (69.7%, 95% CI: 58.4– 79.0%, I2 = 90.7%) and swimming (16.5%, 95% CI: 10.3–25.4%, I2 = 90.8%) were the predisposing factors reported in the most of the studies (Additional File 3).

The estimated prevalence of otomycosis was 58.3% (95% CI: 41.4–73.5%, I2 = 98.2%) (Fig. 2). A total of 968 isolates were detected from otomycosis patients in eight studies. The most common causative agents (pooled proportion of eight studies) were Aspergillus species with a 75.8% (95% CI: 70.3–80.6%, I2 = 70.7%) and Candida species with a 15.3% (95% CI: 8.7– 25.6%, I2 = 63.4%) prevalence (Additional File 3). Since the number of studies were less than 10, we did not perform subgroup analysis or sensitivity analysis.

Fig. 2
figure 2

The pooled prevalence of otomycosis among patients with clinical presentations

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Based on the available data from 20 studies, 46 different species from 11 distinct genera were reported as etiological agents of otomycosis. Out of 1392 isolates, 1372 were identified to the species level, while 18 isolates were only identified to the genus level. Two isolates of aseptate molds were not determined by molecular methods [29]. Eight strains were detected in teleomorph stage, including Emericella nidulans, Eurotium amstelodami, and Eurotium rubrum (teleomorphs of Aspergillus), Trichomonascus ciferrii, Kodamaea ohmeri, Cyberlindnera fabianii, and Millerozyma farinosa (teleomorphs of Candida), and Talaromyces funiculosus (teleomorph of Penicillium funiculosum). We opted to classify these species into the genera of their anamorphs.

The genera with the highest diversity were Aspergillus (23 species), Candida (11 species), and Penicillium (6 species). Additionally, other causative agents of otomycosis include Cladosporium, Fusarium, Cryptococcus, Trichosporon, Scopulariopsis, Galactomyces, Alternaria, and Rhizopus. The most common Aspergillus species were A. niger (n = 352, 30.9%), A. tubingensis (n = 270, 23.7%), and A. flavus (n = 232, 20.4%). The most frequent Candida species were C. parapsilosis (n = 85, 39.7%), C. albicans (n = 66, 30.8%), and C. orthopsilosis (n = 25, 11.7%). Table 3 presents a comprehensive list of all genera and species reported to cause otomycosis.

Table 3 Distribution of species detected by molecular methods as causative agents of otomycosis
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Accurate data for molecular identification of Aspergillus section Nigri were available in 15 studies. Four studies used methods that could not differentiate between A. niger sensu stricto and other species of A. niger sensu lato [23, 24, 27, 29], and one study only included Candida isolates [41]. A total of 565 isolates of Aspergillus section Nigri, consisting of nine distinct species, were reported (Fig. 3). A. tubingensis (n = 270, 47.8%), A. niger (n = 173, 30. 6%), and A. welwitschiae (n = 83, 14.7%) were the most prevalent species.

Fig. 3
figure 3

Distribution of reported species in Aspergillus section Nigri

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Discussion

In this systematic review, we summarized data on various fungal agents confirmed to cause otomycosis in humans. Consistent with previous studies employing non-molecular phenotypic methods [3], our review indicated that Aspergillus species, followed by Candida species, are the etiological agents of the majority of fungal external ear infections. However, our review is more informative than those based on phenotypic studies regarding the species differentiation.

Approximately half of reported Aspergillus strains causing otomycosis belong to Aspergillus section Nigri. This section includes well-known species like A. niger and A. tubingensis, as well as less frequent species such as A. awamori, A. welwitschiae, A. neoniger, A. foetidus, A. piperis, and A. luchuensis. In addition, D’hooge et al. found strains with an identical CaM gene sequence in specimens from otomycosis patients, sinusitis patients, and environment (soil, tree bark, and fish food). They named this new species A. aff. welwitschiae, as it was close to A. welwitschiae on a multilocus maximum-likelihood phylogenetic tree (concatenated alignment of ITS, BenA, and CaM) [38]. Interestingly, similar isolates were later identified by Gits-Muselli et al. in otomycosis cases, as well as respiratory and environmental samples [40].

A notable finding of our review was that, despite A. niger being the most common species overall, A. tubingensis was more frequently identified in studies that differentiated among species within section Nigri. This discrepancy arises because four studies reporting 179 isolates of A. niger did not distinguish among different species of Aspergillus section Nigri. This suggests that a broader range of species might have been identified if A. niger strains had been examined more precisely. A previous review by Kamali et al. also noted that A. tubingensis, rather than A. niger, was the most prevalent member of Aspergillus section Nigri associated with otomycosis [42].

We found that at least nine different species within Aspergillus section Nigri can be responsible for fungal otitis externa in humans. Furthermore, seven isolates could not be speciated even with molecular methods, indicating potential limitations in current identification methods or the presence of undefined species. These findings underscore the high diversity and the challenges in the taxonomy of Aspergillus section Nigri, which comprises at least 28 distinct species [43, 44]. Differentiating the species is especially important because species within section Nigri exhibit varying resistance to antifungals, warranting different treatment approaches [38,39,40].

Our review sheds light on several rare species that were not previously detected in otomycosis patients through conventional methods [3]. For instance, rare species of Aspergillus (A. tamarii, A. nidulans, etc.), Candida (C. ciferrii, C. fabianii, etc.), Penicillium (P. chrysogenum, P. aurantiogriseum, etc.) were reported. Species from rarer genera such as Cryptococcus, Trichosporon, Scopulariopsis, and Galactomyces were also reported. This highlights the value of molecular methods in understanding the diversity of fungi that can cause otomycosis.

Nonetheless, the identification of 18 isolates only to the genus or section level reveals the need for more refined diagnostic techniques. In fact, molecular assays vary in specificity, with many targeting conserved genomic regions such as ITS, which enables genus-level identification but often lack species resolution [45]. This limitation is particularly relevant in the diagnosis of fungal infections, where species-level identification is crucial for effective treatment. For instance, C. glabrata exhibits higher resistance to azoles than C. albicans [46], and distinguishing A. terreus from other Aspergillus species is essential, as the latter is inherently resistant to amphotericin B [47].

Two of the included studies in our review used, in addition to DNA sequencing, matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), which could identify 87.41% and 97.1% of the strains correctly [33, 38]. MALDI-TOF MS is a rapid method that can identify yeasts, molds, and dermatophytes by detecting proteins as bio-taxonomy markers [48]. A meta-analysis of 33 studies showed that this method had a 0.95% (95% CI: 0.94–0.97%) accuracy in diagnosing clinically pathological fungi to the species level.

We demonstrated that less than 60% of patients with the signs and symptoms of otomycosis had a fungal agent confirmed in their ear secretions. Moreover, the variety of potential causative agents suggests that different treatments may be necessary for different patients. Thus, clinical observations alone are insufficient for diagnosing otomycosis, and incorporating molecular assays into the clinical management of otomycosis can be useful. Molecular methods offer a timelier diagnosis compared to culture and facilitate early and accurate identification of causative agents, potentially leading to more targeted and effective treatments and reducing complications and recurrent infections [12].

Interpreting our findings requires consideration of certain limitations. Firstly, the inclusion criteria of our systematic review were restricted to studies published in English, which may have resulted in the exclusion of relevant evidence published in other languages. Additionally, the geographic distribution of studies in this review shows a predominance of research conducted in Iran, with no studies from the Americas or Australia, and only two isolates reported from African countries. This disproportionate representation limits the generalizability of our findings and suggests a potential publication bias. Moreover, the small number of studies included in the meta-analyses precluded an assessment of publication bias using funnel plot asymmetry. High heterogeneity in prevalence estimates, reflected by a large I² statistic, further highlights variability in study populations and diagnostic methods. The results of this meta-analysis are also derived from studies that, overall, exhibit poor quality, necessitating caution in their interpretation and generalization.

Future research should strive to address these limitations by incorporating a more diverse geographic representation and standardizing methodologies to validate and refine findings in this field. Further studies should aim to provide detailed information about the clinical aspects of otomycosis cases, including how molecular methods can aid in tailoring specific treatments and improving patient outcomes. Enhancing the quality of studies through the use of robust study designs, appropriate sampling frames, precise statistical analyses, and comprehensive reporting—while adhering to standardized reporting checklists—will be instrumental in producing reliable evidence and facilitating high-quality meta-analyses in the future.

Conclusions

This systematic review highlights the substantial diversity of fungal agents responsible for otomycosis and underscores the advantages of molecular diagnostic methods in accurately identifying these pathogens. Our findings reaffirm that Aspergillus species, especially those within the section Nigri, are the most prevalent causative agents of otomycosis, while Candida and other less common fungi also play a role. Continued research with expanding the geographic scope and refinement of diagnostic methods is recommended for unraveling the nuances in the etiology of otomycosis and guiding effective treatments.

Data availability

Data is provided within the manuscript and supplementary information files.

Abbreviations

EAC:

External Auditory Canal

DNA:

Deoxyribonucleic Acid

PCR:

Polymerase Chain Reaction

ITS:

Internal Transcribed Spacer

PRISMA:

Preferred Reporting Items for Systematic Reviews and Meta-Analyses

PROSPERO:

Prospective Register of Systematic Reviews

MeSH:

Medical Subject Headings

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Acknowledgements

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Funding

This study was supported by a grant from Iran University of Medical Sciences, Tehran, Iran (grant number 24860).

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Authors and Affiliations

  1. Department of Medical Geriatrics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran

    Tina Nazari

  2. Department of Parasitology and Mycology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran

    Fatemeh Peymaeei, Reihaneh Seiad Ahmadnezhad, Arsalan Bateni Shalmani & Shahram Mahmoudi

  3. Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran

    Romina Ghazi Mirsaid

  4. Student Research Committee, Iran University of Medical Sciences, Tehran, Iran

    Arsalan Bateni Shalmani

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  1. Tina Nazari
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Contributions

SM designed the study and search strategy. TN, FP, RGM, RSA, and ABS contributed to the screening of documents and data extraction. RGM and ABS assessed the quality of evidence. TN and SM contributed to data analysis. TN, FP, and SM drafted the manuscript. All authors proofread and approved the final manuscript.

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Correspondence to Shahram Mahmoudi.

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Nazari, T., Peymaeei, F., Ghazi Mirsaid, R. et al. Otomycosis: a systematic review and meta-analysis of prevalence and causative agents in the era of molecular diagnostics. BMC Infect Dis 25, 544 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12879-025-10954-y

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  • DOI: https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12879-025-10954-y

Keywords

BMC Infectious Diseases

ISSN: 1471-2334

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