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Epidemiology of hearing impairment in childhood.

Consensus about the etiology and prevalence of childhood hearing loss (HL) is difficult to discern. Genuine effects, such as those attributable to environment, are obscured by inconsistencies in data collection and analysis techniques. Prevalence, for example, depends upon test type, hearing loss criteria and age at evaluation. An etiologic classification which clarifies the interaction between time of insult, causation and time of expression of hearing loss is proposed and used for selective review. Much sensorineural hearing loss (SNHL) is of unknown cause. Where the cause is known, genetic causes are common, and influenced by consanguinity. Infectious causes of HL reflect seasonal and epidemic fluctuation, as well as geographic and temporal variation. Non-infectious causes vary more closely with differences in the environment and level of health care. In the western world, the most common cause of conductive hearing loss (CHL) is serous otitis media. In many developing regions, middle ear disease abounds and often is of the dangerous cholesteatomatous type. Certain populations are intermediate, with acute suppurative and chronic otitis media being almost endemic, yet rarely cholesteatomatous.