[Hearing loss in children--epidemiology, age at identification and causes through 30 years].

INTRODUCTION: The survey describes paediatric audiology through 30 years within Copenhagen City concerning epidemiology, age at identification, and causes of permanent hearing impairment in children.

MATERIAL AND METHODS: Three longitudinal ten years birth-cohorts [table: see text] are included: 1970-1979 (n = 69); 1980-1989 (n = 64), and 1990-1999 (n = 104) provided with hearing aids, living in the Copenhagen City at the time of the data collection in January 1982, 1992, and 2002. The cohorts 1970-1979 and 1980-1989 have previously been described (1), whereas the 1990-1999 birth cohort is evaluated as part of a prospective registry study. The estimated prevalences are based on the age-matched background population.

RESULTS: The estimated prevalence of children provided with hearing aids is 1.97/1000 and the estimated prevalence of congenital hearing impairment is 1.50/1000--without longitudinal changes from 1970-1979 over 1980-1989 to 1990-1999. The proportion of at-risk children in the three-pooled birth-cohorts is 63.3%. The median age at identification of the birth-cohort 1990-1999 was 18 months, 1980-1989 16 months, and 1970-1979 43 months. Only 6% of children with congenital hearing impairment born 1990-1999 are identified at the age of six months, and only 27% at the age of one year. An increase in the prevalence of genetic hearing impairment in the cohort 1970-1979 was demonstrated.

DISCUSSION: The prevalence of permanent hearing impairment in childhood through three decades is unchanged, and the age at identification of children with congenital hearing impairments is still delayed. Factors causing hearing impairment demonstrate an increase in genetic factors, which, however, are not significant.