Epidemiological and Etiological Aspects of Hearing Impairment in Patients at the Renaissance University Hospital in N'Djamena, Chad

Introduction

Hearing impairment is the most common sensory disability in the world and is a condition of growing concern [1]. It affects nearly 360 million people worldwide (5.3% of the world’s population) and the majority of cases live in developing countries [2]. Hearing represents the main source for acquisition of language and speaking skills especially during childhood. The hearing-impaired individual is deprived of sound stimulation, and consequently, might present with emotional, social and linguistic disabilities. Therefore, it is of utmost relevance to learn about the epidemiological and etiological factors that cause auditory damage. The causes attributed to hearing loss are many and varied [3, 4, 5, 6]. The main causes include infections/diseases, age-related factors and occupational factors [7]. In sub-Saharan Africa, the prevalence of hearing impairment; defined as hearing loss > 35 dB was estimated to be 15.7% in adults over 15 years of age and 1.9% in children aged 5-14 years [8]. These estimates are based on very few African studies, including school-based hearing screenings. As for the causes, most of them are considered preventable [6]. Certain causes that can lead to hearing loss are defined as preventable and treatable conditions such as middle ear infections leading to conductive hearing loss, infectious diseases leading to sensorineural hearing loss, ototoxicity of drugs and occupational noise exposure.

In Chad, there has never been any national records, systemic scientific assessment of published, publicly available and contributed data, surveys or hospital studies on the prevalence and causes of hearing impairment. This study was conducted to determine the prevalence, describe the socio- professional profile of patients with hearing loss and identify the main etiologies in the Renaissance University Hospital in N’Djamena. In the context of a general lack of epidemiological and etiological data on hearing loss, this hospital study could provide essential data for the development of strategic plans for the management of hearing loss in a sub-Saharan African country.

Materials and Methods

This was a prospective cross-sectional study, conducted from November 1st, 2020 to October 31st, 2021, at the ENT and Head and Neck Surgery Department of the Renaissance University Hospital in N’Djamena, Chad. All patients aged 6 years and above that came for consultation for hearing loss were included. Patients under 6 years of age, known and documented psychiatric disorders, active substance abuse, who could not be expected to have the ability to follow the instructions in a relaxation training and cognitive deficits were excluded. For each patient, a clinical consultation, general physical examination, otoscopy and audiometry was performed. In case of doubt about the etiological diagnosis, the examination was completed by a computed tomography (CT) scan and/or magnetic resonance imaging (MRI) of the petrous temporal bone. Data were collected on pre-established forms including epidemiological parameters (age, sex, occupation), patient’s medical history, exposure to high levels of noise, clinical and audiometric data and the results of the medical imaging. Linear tone audiometry was performed using a Model AC50-D® audiometer in a Puma® Model PRO 25 soundproof booth. The average hearing loss in each ear was calculated by dividing the sum of the measured deficits in decibels (dB) at the frequencies of 500, 1000, 2000 and 4000 Hz by 4. The World Health Organization’s criterion was used to classify the severity of hearing loss for each ear as mild (26 to 40 dB), moderate (41 to 60 dB in adults and 31 to 60 dB in children under 15 years of age), severe (61 to 80 dB) or profound (81 to 120 dB). Above 120 dB nothing is perceived and therefore causes total deafness or cophosis. In cases where the classification of the severity of hearing loss differed between two ears, the severity of the bilateral hearing loss was based on the better ear.

The data were analyzed using SPSS version 26.0. Descriptive frequency statistics and cross-tabulations were performed. The chi-square test was used for comparison of the different proportions. A p-value of less than 0.05 is considered significant. All patients had given a verbal consent to participate in the study and to have their data published. In the case of children, a parental consent was obtained. The study was authorized by the Faculty of Human Health Sciences in N’Djamena. The study has complied with the 2013 Declaration of Helsinki.

Results

During the study period,188 patients had presented with hearing loss out of a total of 836 patients seen in ENT consultations, i.e., a hospital prevalence of 22.5%. Males accounted for 75.5% (n=142) or a sex ratio (male/female) of 3.08. The median age was 35 years with an age range of 7 to 90 years. The distribution of patients by age group is shown in (Figure 1).

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Unilateral hearing loss was observed in 51.1% of cases (n=96) and bilateral hearing loss in 48.9% of cases (n=92). Conductive hearing loss was noted in 46.8% (n=88) of the patients, sensorineural hearing loss in 37.2% (n=70) and mixed hearing loss in 16% (n=30) (Table 1). The hearing loss was moderate in 57.4% (n=108) of the patients. Figure 3 shows the degree of hearing loss.

Regarding the etiology, chronic suppurative otitis media was observed in 24.5% (n=46) of the patients, presbycusis in 12.8% (n=24), seromucous otitis media in 11.7% (n=22), acoustic trauma in 10.6% (n=20) and head trauma in 9.6% (n=18). Table 2 provides a complete list of etiologies of hearing loss and their frequencies. According to the type of hearing loss, the main causes of conductive hearing loss were chronic suppurative otitis media (45.5%) and seromucous otitis media (25.0%), the main causes of sensorineural hearing loss were presbycusis (34.3%) and acoustic trauma (28.6%), and the main causes of mixed hearing loss were head trauma (40.0%) and congenital deafness (33.3%). Figures 4-6 provide information on the different etiologies of conductive, sensorineural and mixed hearing loss. The etiologies of hearing loss in our patients were associated with age (p < 10-3), occupation (p < 10-3) and degree of hearing loss (p < 10-3). Further details are given in Tables 3-5.

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*Acute acoustic trauma (n=14; 7.4%); chronic acoustic trauma (n=6; 3.2%); **Meningitis (n=4; 2.1%); chicken pox (n=4; 2.1%); rubeola (n=2; 1.1%). Table 2: Distribution of cases according to the etiology of hearing impairment.

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Χ2 = 93,262 ; ddl=42 ; p < 10-3. Table 3: Etiologies of hearing impairment according to age groups.

Χ2 = 142,926 ; ddl=63 ; p < 10-3. Table 4: Etiologies of hearing impairment according to the patient’s occupation.

Χ2 = 81,610 ; ddl=28 ; p < 10-3. Table 5: Etiologies of hearing loss according to the degree of hearing impairment.

Discussion

To our knowledge, in Chad, this is the first study done to examine the prevalence and etiologies of hearing loss in hospitals. Using a threshold of 26 dB, the prevalence of hearing loss obtained in this study was 22.5%. The prevalence of hearing impairment varies considerably between studies in sub-Saharan Africa; 3.6% in Cameroon [4], 5% in Mozambique [9], 17.5% in South Africa [10] and 18% in Uganda [11].

Several factors contribute to this variation in prevalence across studies, including the different study settings (community, school or hospital) and the threshold used to measure hearing loss. Using a low threshold such as 25 dB would identify a mild hearing loss and produce a higher prevalence, whereas a pure tone threshold of 40 dB would result in a lower prevalence where only moderate and severe hearing loss would be considered. In any case, sub-Saharan Africa remains one of the regions of developing countries where the prevalence of hearing impairment is significantly higher than in developed countries. Some available reports indicate a prevalence of 11.5%-20.3% for adults (≥ 15 years) and 1.2%-3.0% for children (5-14 years) in low-income countries compared to 4.0%-6.4% for adults (≥ 15 years) and 0.3%-0.6% for children (5-14 years) in high-income countries [12]. In the United States, the prevalence of hearing impairment is estimated to be 2.5% in people over 12 years of age [13]. The high prevalence of hearing loss in sub-Saharan Africa could be attributed to poor health systems that are not always adequately equipped to prevent, detect and manage the causes of hearing loss [14].

As for the socio-professional profile of the patients, the study showed a predominance of males (sex ratio = 3.08); students represented 24.4%, soldiers represented 17% and civil servants represented 16% of the patients. The high presence of military civilians in this series is due to the fact that our tertiary care hospital has been receiving a large number of war casualty victims of the terrorist attacks by the Boko Haram sect in the Lake Chad region for the past three years. Previous research has shown that men are more likely to have hearing difficulties than women partly due to increased exposure to ear diseases [15], noisy workplaces [16, 17], military service, and the use of firearms [18].

In this study, regarding the etiologies of hearing loss, infectious diseases were in the forefront, followed by acoustic trauma, cranial or auricular lesions; presbycusis; congenital and/or genetic conditions, and the use of ototoxic drugs. All of these conditions are widely cited in the literature but in different proportions [2, 19, 20, 21, 22, 23, 24, 25]. It is difficult to make meaningful comparisons because of variations in the methods used in different studies. However, it should be noted that, as with other studies of hearing impairment in sub-Saharan Africa, most of the causes found in this study are preventable. These include chronic suppurative otitis media, infections leading to sensorineural hearing loss, such as meningitis, measles, and chicken pox, noise exposure and drug ototoxicity. Furthermore, this study also showed that the causes of hearing loss were associated with age groups, occupation and degree of hearing loss. Infectious diseases were the only cause of deafness in children aged 6 to 15 years and the main cause in students. While in other studies, genetic conditions and abuse of ototoxic drugs were associated with infectious diseases in this age group [26, 27]. Over the age of 65, presbycusis seemed to predominate and was more prevalent in the retired group. Some authors question the causal mechanism of hearing loss in the elderly and seek to understand the link between age-related hearing loss and cognitive decline [28]. The main causes of hearing loss in the military were noise injury and acoustic blast trauma. The exposure of military personnel to noise trauma is well reported in the literature [29, 30, 31]. Drug ototoxicity was noted in patients with no or low income (students, unemployed and security guards). In our context, poverty is a source of self-medication and patients have easy access to anti-malarial drugs, aminoglycosides such as gentamycin and loop diuretics such as furosemide, thus exposing them to drug-induced ototoxicity, which is probably the most functionally dangerous cause of hearing impairment in our patients (6 out of 8 patients that were drug-induced had cophosis). The rest of the etiologies resulted in moderate to profound degrees of disabling hearing impairment with the exception of cerumen impaction, which only resulted in mild hearing loss.

Conclusion

Hearing impairment in adults and children is common at the Renaissance University Hospital in N’Djamena, Chad. It affects men more than women. The causes are dominated by infectious diseases, presbycusis and noise injury. This study reveals a large proportion of preventable hearing loss, thus, highlights the importance of maximizing efforts in primary health care services to prevent or treat preventable causes in a timely manner. There is a clear need for a population- based study at the national level to estimate the prevalence of hearing impairment in Chad.

Declarations

• Ethics Approval and Consent to Participate This study has been authorized by the Faculty of Human Health Sciences in N’Djamena (Reference n° 276/CMT/ PCMT/PMT/MESRI/SE/DGM/UNDJ/SG/FSSH/21) and has been complied with the 2013 Declaration of Helsinki. All the patients were consented to participate in the study.
• Consent for Publication A verbal consent was obtained from participants for the publication of the data.
• Competing Interests The authors have nothing to declare.
• Funding The authors did not receive support from any organizations for this study.
• Author Contributions All authors contributed to the design and development of this work. AAT was responsible for analyzing the data and writing the manuscript. The preparation of the material and data collection were carried out by BA and YAA. All authors have read and approved the final manuscript.