The exposed group consisted of 70 military musicians. Finally, 55 military musicians were able to participate in the study in the exposed group because 15 of them were not available, for a coverage rate of 78.6%.

The control group consisted of 55 non-musicians from the First Motorized Intervention Battalion.

Of a total of 110 military personnel surveyed, the mean age was 34.3 ± 6.2 years (range 26 - 50 years). The mean age was 35.9 ± 7.0 years and 32.7 ± 4.8 years for the exposed and control groups, respectively. In the exposed group, there were fewer young soldiers compared to controls (54.5% were under 35 years of age versus 67.3%). The sex ratio was 17.3 i.e. 10 men for a woman in the exposed group and 54 men for a woman in the control group. The exposed group was older than the controls (56.4% versus 47.3%). The two groups were not statistically different with respect to age, gender and length of time in Benin army. Table 1 presents the socio-demographic and professional characteristics of the military personnel surveyed.

Sound exposure concerned exclusively the exposed soldiers. Musical instruments were “wind instruments” in 74.5%, “percussion” in 23.6% and “string instruments” in 1.8%. The wind instruments were bass, trumpet, bugle, trombone and

*Peason’s Chi-squared Test; **Student’s Test.

saxophone. Among the percussion instruments were the bass drum, the drum and the drum set. The stringed instrument used was the guitar.

More than a third of the military musicians (36.4%) had been in the music squadron for 5 to 10 years. The average length of service in the music squadron was 11.5 ± 6.7 years with extremes of 1 and 25 years. On average, military musicians practiced music for 4 days per week with extremes of 2 to 6 days. The average daily occupational noise exposure was estimated to be 4.6 ± 0.8 hours, ranging from 4.1 to 5.1 hours. None of the musicians used personal hearing protection equipment (PPE) on a routine basis.In spite of the professional exposure, it was noted that almost all of the military musicians (92.7%) were involved in a musical activity outside the music squadron, in particular in a church choir (Table 2).

*Bass, trumpet, bugle, trombone, saxophone; **Bass drum, drums and drumset; ***Guitar.

Noise level

The average noise level during training ranged from 89.1 dB (A) to 116.4 dB (A).

· Anamnesis

No service members reported a history of long-term ototoxic drug use, head injury, nagging or repeated otologic infections, tumor, or otologic surgery.

· Functional signs

Hearing loss was the most common and most important complaint in the exposed group (34.6% vs. 7.3%). The exposed group was 6.73 times more likely to have a hearing loss than the controls (Table 3).

· Physical examination

Otoscopic follow-up noted one case of otitis externa and one case of acute otitis media in the exposed soldiers. ENT examination remained normal in all soldiers in the control group. The otitis externa was treated locally with anti-inflammatory drops with a good clinical evolution. The otalgia, redness and congestion of the external acoustic meatus involved improved within eight days. The case of acute

*Peason’s Chi-squared Test; **Fisher’s Exact Test.

otitis media was also cured after ten days of antibiotic therapy with amoxicillin-clavulanic acid combined with paracetamol. The military personnel involved performed the audiometry at a distance from the infectious episode.

· Audiometric parameters

Baseline pure tone audiometry revealed 30 cases of hearing loss, 23 of which were in the exposed population (Table 4). The hearing loss was typically mild (p = 0.002) and bilateral (p = 0.007).

· Analysis of hearing loss on pure tone audiometry

There was a statistically significant relationship between hearing loss and noise exposure in both ears (Table 5).

· Factors Associated with Hearing Loss

*Fisher’s Exact Test.

*Student’s Test.

In addition, there is a statistically significant relationship between hearing loss, age and duration of exposure at the exposed level (Table 6).

*Correlation coefficient. *Pearson correlation.

Age

The study was conducted on a sample of young adult military personnel in full professional activity. Ndiaye et al. [5] in 2013 and Diop et al. [6] in 2017 in Senegal reported respectively during their studies on military personnel average ages of 39.7 years and 36.6 years similar to the average age found in our study. These study results could be explained by the fact that in Benin, recruitment into the army is open to young people between the ages of 18 and 25 for a period of 30 to 35 years depending on the military rank. The age homogeneity of the two groups was simply achieved by the fact that they all came from the same Beninese military population. Gonçalves et al. [7] in a retrospective cohort study of hearing threshold analysis in Brazilian military musicians, also found age homogeneity between the military musician group (34.9 ± 7.8 years) and the control group (35.4 ± 9.4 years). The inclusion criteria excluded military personnel, whether musicians or not, over 50 years of age. These were military personnel on the verge of retirement, for whom presbycusis could be a confounding factor. Although there is a large inter-individual variability, the age of onset would be around 50 years [8]. In the United States, presbycusis affects about half of the population over the age of 65 [9]. It is recommended that adults be screened systematically for hearing loss from the age of 60 [10].

Gender

The low female representation in the sample is a reflection of the gender distribution in Benin Army. Like all occupations requiring physical strength, the military function has long been considered a “man’s job” and every man is potentially a warrior [11]. However, one cannot deny the historical role played by the Amazonian women of Dahomey in certain military operations in Benin’s history. The low participation of women in music is also a fact explained by authors including Sergeant et al. [12] in 2019 in England. These authors [12] counted 39.7% women out of a total of 3420 musicians in 40 world-class symphony orchestras spread across three regions (the United Kingdom, Europe and the United States). The sexist reasons that historically justified discrimination against women have been dispelled since the second half of the 20th century [12]. However, the influence of gender as a biological variable in the occurrence of deafness is still poorly understood [13]

The measured sound levels are above the recommended standards according to the daily exposure time, since for a maximum daily exposure time of one hour, the equivalent weighted sound level should be 94 dB (A). Gonçalves et al. [7] evaluated the sound pressure levels to which military musicians in Brazil were exposed using an integrated sound level meter. They reported that, during rehearsal sessions lasting 4 hours, these levels varied from 90.1 to 110.3 dB (A). A Canadian study by Qian et al. [14] found that the average sound levels of ballet orchestra musicians playing wind instruments for 3 hours were between 88 and 94 dB (A). In Germany, Schmidt et al. [15] measured the noise exposure of symphony orchestra musicians and reported sound levels between 82 and 98 dB (A). Nataletti P et al. [16] reported in a study of national orchestra musicians in Italy that musicians are subjected to high personal daily sound levels that can systematically exceed 85 dB (A) in the case of percussionists. In Portugal, Rodrigues et al. [17] also reported high noise levels in the context of an evaluation of the exposure to noise of musicians in a Portuguese symphony orchestra. Measurements made with the dosimeter and a sound level meter in this study noted for wind instruments, a sound level that averaged 92.7 ± 2.77 dB (A) and 90.0 ± 2.93 dB (A) for percussion. Lower noise levels were measured for string instruments, which were evaluated at 85.4 ± 3.40 dB (A). The similarity of these results showing overall exposure to high sound intensities could be due to the rather similar instrumental composition that exists in these different groups. On the other hand, these high and fluctuating sound levels could be explained by the complexity of the sounds emitted by a music group. Thus, it should be noted that several factors make the sound level emitted by a group of musicians very changeable. These include the variability of instrumentation within bands, the position of musicians in relation to bands or in an orchestra, the chosen musical repertoire, the location of rehearsal or performance, and individual variability such as musician fatigue. In this study, military musicians were exposed to these sound levels that were too high for the duration of exposure. This level of exposure is sufficient to generate permanent hearing impairment. Thus, the Brazilian study by Gonçalves et al. [7] found greater hearing loss in military musicians who had been exposed for more than 21 years. A German study evaluating the hearing status of professional classical orchestra musicians and music students showed that more than 50% of the musicians had a hearing loss of 15 dB (A) or more [18]. The highest losses were found among string and brass instrument players. These authors therefore concluded that musicians need the same health care for their hearing as workers in noisy industry. Reinhard Müller and Joachim Schneider [19] conducted a prospective study on a group of 36 German military musicians seen at 13-year intervals. Despite the high noise levels, the average hearing ability of the 36 military musicians during the investigation period deteriorated only slightly in the noise-sensitive frequencies (3, 5 and 6 kHz). These results suggest that music may be less harmful than industrial noise.

In our sample, none of these music professionals routinely wore hearing PPE. The survey also shows that noise exposure goes beyond the military music profession for some subjects. Indeed, musical initiation elicited dual noise exposures: professional and extra-professional. This study did not quantify loudness in the context of music practiced for recreational and/or religious purposes.

The main otological symptoms found in military musicians were deafness (41.8%) followed by tinnitus (20%) and headache (7.3%). These are classic and well known causes of occupational exposure to noise pollution [20]. Moreover, there is a statistically significant relationship between the occurrence of deafness and noise exposure (p < 0.001). Souleymane et al. [21], in analyzing the health and social impact of noise pollution among power plant workers in the city of Ouagadougou in Burkina Faso, reported 11.7% headaches and 34% deafness. Foma et al. [22] in a hospital study found that tinnitus was frequently associated with deafness and headache in 66% and 31.1% of cases respectively and that noise trauma was the main etiology. It should be noted that deafness induced by occupational noise exposure has been reported extensively in the literature [3] [23] [24]. Tinnitus is also a recurrent problem [25].

Numerous studies have reported a similar symptomatology to ours but in different proportions. In Brazil, in 2009, musicians of military bands were also evaluated. A study with 50 subjects had revealed that 76% of the musicians had tinnitus and 54% reported hearing difficulties [26]. Also, Luders D et al. [27] found in 2016 as auditory symptoms in a study with 100 musicians, 72% tinnitus and 67% intolerance to loud sounds. In Australia, O’Brien I et al. [28] reported on 367 musicians from eight professional orchestras, 43% deafness, 42% tinnitus experienced sometimes and 9% persistently.

Repetitive noise exposure is one of the major preventable sources of permanent hearing loss. The collected hearing losses were significantly higher in the military musician group (41.8%). The study also found a statistically significant relationship between hearing loss and noise exposure (p = 0.001). Also, it should be noted that the military musician had a 4.50 times greater risk of developing a mild hearing loss than a non-musician (OR 95% = [1.78 - 12.57]). The risk of sensorineural hearing loss was 5.25 times higher in the noise-exposed group compared to the control group (OR95%= [1.71 - 19.84]). This could be explained by the fact that noise causes damage to the inner ear which leads to sensorineural hearing loss [20] [24]. Indeed, in case of auditory nuisance, the hair cells of the inner ear are damaged and cannot regenerate. Recent studies have demonstrated a vulnerability of the inner ear during long exposures such as the case of the musicians in the present study [29] [30] [31]. Russo F et al. [32] [33] also reported the existence of sensorineural hearing loss in 2012 and 2017 in their study of 52 musicians of the National Ballet Orchestra of Canada.

Classically, noise-induced hearing loss is a bilateral and symmetrical hearing loss [24] [34]. The bilateral and symmetrical hearing losses in the study were ten times greater in military musicians (18.2%) than in non-musicians (1.3%). The asymmetry observed in our study (23.6% in the exposed group and 10.9% in the controls) does not call into question their aetiology [20] [35] [36]. The characteristic of symmetry of the hearing loss should therefore be considered with reservation as being specific to a noise-induced hearing loss. This risk of military music-induced hearing loss can be as high as 14.54 times compared to the control group [7]. However, this risk is non-existent at the beginning of the career [37]. The deafness found in our sample was proportional to the age and duration of exposure at the level of the exposed. Sayegh Ghoussoub M et al. [38] in Lebanon published similar results among musicians playing a wind instrument in the orchestras of the national conservatory of the Lebanese army and the internal security forces. Even though deafness is noise-induced, the age of the musician is an additional etiological factor [39].

Hearing damage related to sound trauma is manifested by a notch centered at 3, 4, or 6 kHz. The 4000 Hz frequency is the most affected and is therefore found in the center of the notch on tone audiometry [24]. The more intense and repeated the sound trauma, the more these notches increase in width and depth, indicating a greater destruction of the hair cells in this most fragile frequency zone of the ear [40]. The study by Schmidt JH et al. [41] found that occupational noise exposure in five groups of symphony orchestra musicians led to noise-induced hearing loss with higher hearing thresholds between 3 and 6 kHz. The largest noise-related effects on audiograms in the said study were shown at 3 and 4 kHz. For Emmerich et al. [18] and Jansen et al. [42], hearing loss was predominant at 4 kHz or 6 kHz. This aspect appears to be the most specific for noise-induced hearing loss.

Conventional audiometry showed that the most significant hearing loss in the military musicians in our study was in the 250 Hz and 500 Hz frequencies. In all cases, primary prevention and early detection with a view to appropriate treatment will help to maintain better hearing health. The golden rule is regular medical follow-up and the use of hearing protection equipment. Hearing assessment should be done at the first sign of doubt, without wasting time, and should include a clinical examination and pure tone audiometry. Hearing protectors specially designed for music professionals help maintain good hearing and acoustic accuracy. They can be custom-made based on the impressions of the external acoustic meatus. Workplace noise legislation in our country does not provide specific guidance for musicians or a code of conduct that sets general guidelines on how musicians should be protected from noise exposure. This is particularly critical since the hearing ability of musicians is crucial to their professional activity and performance.