In a cross-sectional convenience sample of mostly elderly people from ten rural towns in the German state of Brandenburg, we observed a high proportion of patients with hearing loss. The majority of patients with hearing loss did not have hearing aids. The proportion of underserved patients decreases with the availability of health professionals in the towns.
The proportion of patients with hearing loss was 97%, where hearing loss was defined as a threshold of 30 dB or more in at least one ear and at least one of the frequencies 0.5, 1.0, 2.0 and 4.0 kHz, which is one indicator for qualifying for a hearing aid. In the HörMat study , a hearing loss of 77.8% in patients older than 60 years with hearing impairment defined as ≥ 25 dB in one of the frequencies between 0.5 and 4.0 kHz was observed. Lower proportions ranging between 16 and 25%, depending on age and definition of hearing loss, were observed in a recent review . Sohn and Jörgenshaus , who included patients aged above 14 years in a primary care practice, diagnosed hearing loss in 19% of their patients with thresholds of ≥ 40 dB for one of the frequencies 0.5, 1.0, 2.0 or 4.0 kHz. In the HörSTAT study , patients between 18 and 97 years of age were included (Table 3).
The preceding summary illustrates the heterogeneity of definitions for hearing loss used in different studies, which complicates the interpretation of corresponding proportions. We chose our definition, because it is used by German health insurances for the indication of a hearing aid. The study with the most similar definition of hearing loss , i.e., ≥ 25 dB instead of ≥ 30 dB, also observed a high proportion of patients with of hearing loss (77.8%), albeit lower than the 97% observed in our study. An explanation could be older age and possible self-selection in our study. If we apply the 25 dB threshold used in the HörMat study  to our data, the proportion of patients with hearing loss is 98% (95% CI 97–100%). The proportion of disabling hearing loss according to the World Health Organization, i.e., more than an average of 40 dB for frequencies 0.5, 1, 2 and 4 kHz, is 59% (95% CI 52–66%) in our data (https://www.who.int/pbd/deafness/estimates/en/, accessed Dec 17, 2020). Studies with substantially lower proportions of hearing loss either based their definition on the average over four frequencies rather than at least one frequency , used subjective criteria [13, 14], or used substantially higher thresholds (e.g., ≥ 40 dB ). Therefore, the observed proportion of patients with hearing loss in our study is indeed very high compared to other studies but is not per se inconsistent.
The observed proportion of subjects without hearing aids among all subjects with hearing loss greater or equal than 30 dB (77%) was higher compared with two studies identified in the review by Löhler et al. . Von Gablenz et al.  reported 5.8% (age 60–69 years), 18.3% (70–79 years) and 32.6% (≥ 80 years) in the HörSTAT study, while Sohn and Jörgenshaus  observed that 2% of all participants had a hearing aid while the proportion of patients with of hearing impairment was 16%.
Our data show that untreated hearing loss is common in rural areas and may reach close to 100% in areas with no hearing aid technician and no ENT physician. This is consistent with Chan et al. , who observed that distance to hearing healthcare services was associated with the timing of acquisition of hearing aids. Key motivators to seek care include degree of hearing loss, self-efficacy, family support, and self-recognition of hearing loss .
The need for optimal rehabilitation of hearing impairments is not only important for optimal sound transmission to the auditory cortex. In addition, it is known that the auditory impulse on vestibulospinal reactions is an important component in balance regulation . Dawes et al.  observed an association between hearing aid use and better cognition. Also, hearing aid use is associated with delayed diagnosis of dementia, depression and anxiety .
Our preliminary study includes only a small number of self-selected participants. It is possible that the observed proportion of hearing loss is an overestimate, since hearing-impaired persons may have been particularly attracted by the offer of a cost-free audiometry test. Moreover, only limited demographic and other patient-specific information was recorded, and was entirely missing for a fraction of the subjects. However, our study has several strengths. Audiometry was performed by ENT physicians on standardized equipment in a vehicle which was specifically noise-insulated for this purpose. The high proportion of hearing-impaired persons allowed us to estimate the percentage of underserved patients with high precision (77%, 95% CI 69–84). The knowledge about the availability of hearing aid technicians and/or ENT physicians in the selected areas enabled us to evaluate determinants of underserving in Germany.
Although our study took place in a local context, the relevance of the objective goes far beyond the particular region studied. Thinly populated areas are common in all European countries (on average 30% of the area), and population density is known to be inversely correlated with health in industrialized countries . The patterns observed here may, therefore, generalize to substantial proportions of the population in countries such as Germany, France, the Netherlands, Spain, and the UK.
Hearing loss can have profound effects not only on interpersonal communication, but also on health, independence, wellbeing, quality of life, and daily function. It is a field in which modest interventions have the potential of producing a substantial reduction in the global burden of disease. Large representative studies are needed, particularly in rural areas, to assess the level of hearing loss, the fraction of persons without adequate help and the reasons for this, so that interventions, such as mobile diagnostic units, can be designed and evaluated. These interventions aim to improve the hearing of the population to increase their quality of life and to prevent severe morbidity known to be associated with untreated hearing loss, such as falls, dementia, depression, and other diseases.