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

Hearing impairment is the most common disorder of sensorineural function an d is an economically and socially important cause of human morbidity. A lar ge-scale epidemiological survey of hearing loss was conducted with 126,876 unselected subjects (63,741 male and 63,135 female) from Sichuan, China. Th e 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 sens orineural, and in 20.39% (849 of 4,164), it was conductive; the remaining c ases (6%) were mixed hearing loss. Bilateral loss was found in 74.5% of cas es 13,103 of 4,164). In 63.79% of cases (2,656 of 4,164). the degree of hea ring loss was less than 55 dB hearing level (HL), and in 5.67% of cases (23 6 of 4.164), it was greater than 90 dB HL. The prevalence of hearing loss i n 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 gene tic hearing loss was 0.28% (349 of 126,876). Persons who lived in the flatl ands 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 hi gher prevalence of hearing loss. Presbycusis, otitis media, and genetic fac tors 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 etiolog ic 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.