Epidemiological studies on hearing impairment with reference to genetic factors in Sichuan, China.

Hearing impairment is the most common disorder of sensorineural function and is an economically and socially important cause of human morbidity. A large-scale epidemiological survey of hearing loss was conducted with 126,876 unselected subjects (63,741 male and 63,135 female) from Sichuan, China. The overall prevalence of hearing loss was 3.28% (4,164 of 126,876), and the prevalence increased with age, reaching 12.8% (1,465 of 11,421) at 60 years of age. In 73.03% of all cases (3,041 of 4,164), the hearing loss was sensorineural, and in 20.39% (849 of 4,164), it was conductive; the remaining cases (6%) were mixed hearing loss. Bilateral loss was found in 74.5% of cases (3,103 of 4,164). In 63.79% of cases (2,656 of 4,164), the degree of hearing loss was less than 55 dB hearing level (HL), and in 5.67% of cases (236 of 4,164), it was greater than 90 dB HL. The prevalence of hearing loss in childhood (<15 years of age) was 0.67% (227 of 34,157), of which 57.7% of cases were conductive and 38.8% were sensorineural. The prevalence of genetic hearing loss was 0.28% (349 of 126,876). Persons who lived in the flatlands appeared to have a higher prevalence than those who lived in the hills. Several ethnic groups, including Tibetans, the Yi, and the Lisu, had a higher prevalence of hearing loss. Presbycusis, otitis media, and genetic factors were the most commonly recognized causes of hearing impairment overall, but otitis media and genetic factors were the main causes of hearing loss in children. Causes for the observed differences in prevalence and etiologic factors between China and industrialized countries will be discussed. In China, infections and genetic factors appear to be of major importance as causes of hearing loss.