While working on my current grant application, I was astounded by the prevalence of hearing impairment in the United States. Additionally, this begged a question: Is hearing impairment currently underdiagnosed, overdiagnosed, or neither? After perusing the literature, I found the answer to be fairly complicated. While it is believed that presbycusis (age-related hearing loss) is underdiagnosed in the U.S., the prevalence of hearing loss appears to be fairly high in this country when compared with worldwide statistics (over 30 million in the United States, with about 275 million around the world). Is this due to relatively better diagnosis in the U.S., or is there something else going on? Here, I’ll delve into that question, through the following measures:
- Statistics on hearing impairment of all types in the United States
- Statistics on hearing impairment of all types in various other countries
- Comparison of screening and management in these regions
It is helpful to consider these basic data before moving on to determining any real differences between the countries. When discussing rates of change in prevalence or incidence of disease, it is helpful to first determine the effects of diagnostic bias. Nonetheless, I hope readers will leave with the impression that hearing loss is a major problem, one that will become more apparent as our population ages.
For the purposes of this post, remember that hearing loss is defined as a hearing threshold greater than 25 dB, where 0 dB is defined as the sound pressure at which young, healthy listeners hear that frequency 50% of the time. Functional impairment, however, is that which begins to impair the ability to understand conversational sound levels at 50-60 dB. A recent review of hearing loss in the United States estimated that over 10% of the population has bilateral hearing loss (>25 dB HL), and over 20% are estimated to have at least unilateral hearing loss. This staggering statistic increases to over 55% in those aged at least 70, increasing to nearly 80% by the age of 80. With an aging population in the United States, this becomes a major public health concern.
The causes of hearing impairment include genetic, drug-induced, and noise-induced hearing loss. With the increased use of overloud noise, noise-induced hearing loss has become more prevalent over time. However, nonsyndromic and syndromic genetic hearing loss accounts for about 50% of impairments in children. Remaining environmental causes include “TORCH” organisms and other neonatal infections. Nonetheless, the problem is a vast one, an issue that will grow as this population ages.
Considering the vastness of this problem, how well do we screen for it? The answer is that we do a poor job of it. Only 9% of internists offer screenings to those aged 65 and older, and only 25% of those with hearing impairment that could be treated with hearing aids actually use hearing aids. This is a failure in both screening and management. Thus, we must reiterate the prevalence of this health condition and do what we can to improve the current state of underdiagnosis and undertreatment. Thus, to answer the question above, we still do not do a stellar job in our screening of hearing loss.
How do we compare with other countries? Is hearing loss more prevalent in the United States, even though our screening programs are not ideal? It’s actually the opposite. Hearing loss is more prevalent in middle-income and lower-income countries, but the screening there is so poor that the numbers are staggeringly underreported. Compared with the rate of about 10%-20% in the United States, prevalence increases to over 25% in southeast Asia, 20-25% in sub-Saharan Africa, and over 20% in Latin America. The WHO reports a value of about 275 million people with moderate to severe hearing impairment (note that the values listed above are for mild hearing impairment) and estimates that approximately 80% of this is in less wealthy nations. If we include all those with any type of hearing impairment (including mild, >25 dB HL), the number rises to 500-700 million people around the world (with 30-40 million in the United States). There is also very little information regarding hearing aid use in low and middle income countries (excluding Brazil), since many of these countries tend toward worse management than what we have in the United States.
When discussing the “global burden of disease,” hearing impairment hits the nail on the head. It is a health condition that affects all countries and in much the same way. Though there is a lower prevalence in high-income countries, consider that 1 in 5 people will succumb to some form of hearing loss. We must therefore implement increased standards for screening and management of this condition.