The epidemiology of childhood hearing impairment: factor relevant to planning of services.

In the Nottingham District Health Authority we found that one in 943 babies born between 1983-1986 have a sensorineural or mixed hearing impairment (at 50 dB HL or greater in the better ear averaged over the frequencies 0.5, 1, 2, 4 kHz) that is either congenital or progressive in nature. If this figure is broken down between non-neonatal intensive care unit babies and neonatal intensive care unit (NICU) graduates, we find that one in 174 NICU graduates have a hearing impairment compared with one in 1278 non-NICU babies. Excluding from the non-NICU baby population those with a known family history of hearing impairment, and those with a known relevant syndrome at birth, there is a 10.2 to 1 odds ratio for babies in NICU to have such hearing impairments compared to this restricted 'normal' baby population. In addition NICU babies with a hearing impairment were considerably more likely to have another disability (odds ratio 8.7 to 1). Acquired sensorineural or mixed impairments comprised about 9% of the children with impairments by 3 years of age. Twenty per cent of the patients seen at the Children's Hearing Assessment Centre (CHAC) with better-ear impairment of 95 dB HL or greater had acquired hearing impairments. The mean age of referral for congenital hearing impairments was found to be a function of severity and NICU status. For children with better-ear hearing impairments of 80 dB HL or greater, the mean and median ages of referral were both 8 months (s.d. 4 months).