Introduction

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Permanent childhood hearing impairment can have a devastating impact on communication skills,¹ educational attainment,² and quality of life, ^{3 4} with a high cost to society.⁵ Improved outcomes for children with congenital impairment are associated with confirmation and intervention by 6 months of age.⁶ Yet the median age of confirmation of congenital impairments has exceeded 18 months, even in regions of the United Kingdom and United States with good paediatric audiology services. ^{7 8} Universal neonatal hearing screening ^{9 10} has the potential to reduce the age at confirmation of congenital impairments.¹¹ However, not all hearing impairments manifest themselves at birth, and screening programmes must be complemented by services that can confirm and manage cases where impairment first shows itself postnatally. No national register of hearing impaired children exists for the United Kingdom, and accurate estimates of the prevalence of permanent childhood hearing impairment and of its profile across age and degree of impairment are unavailable. We have provided such estimates at a time when paediatric audiology services in the United Kingdom are being transformed by the introduction of universal neonatal hearing screening¹² and the modernisation of hearing aid services.¹³

Previous studies of the prevalence of permanent childhood hearing impairment display two limitations. ^{7 8 14-16} Firstly, they ascertained relatively small samples (under 700 children) and so did not define the relation between prevalence, age, and degree of impairment precisely. Secondly, they did not estimate the extent of underascertainment. We examined these issues by estimating prevalence from a total ascertainment of hearing impaired children in the United Kingdom (>17 000) and by employing capture-recapture analysis ^{17 18} to adjust for underascertainment. Full details of these methods can be found in the long version of this paper on the BMJ's website. We estimated the prevalence of confirmed cases of permanent hearing impairment, including congenital, late onset, and acquired cases.

	Methods

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Case definitionCases were children resident in the United Kingdom during 1998, born between 1 January 1980 and 31 December 1995 inclusive, with confirmed permanent bilateral hearing impairment exceeding 40 dB HL (hearing level).

View larger version (19K): [in this window] [in a new window]   Profiles of observed and adjusted prevalence of permanent childhood hearing impairment with age and by degree of impairment (all: >40 dB HL; moderate: 41-70 dB HL; severe: 71-95 dB HL; profound: >95 dB HL).20 Points plotted as filled circles were excluded from some analyses

AscertainmentChildren were ascertained through professionals with responsibility for the provision of audiological health care (n=473) and education (n=434) to hearing impaired children. During 1998, professionals were asked by mail to complete a one page form for each case known to them. We sent one reminder to non-responders after four months.

AnalysisWe applied capture-recapture techniques using conventional formulas to estimate the size of populations from restricted samples.¹⁷ We used live birth statistics¹⁹ to convert counts of children into prevalence rates per 1000 live births.

	Results

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Response rate
Geographical coverage was comprehensive: professionals reported children from every postcode area in the United Kingdom, and only two of 122 postcode areas were not covered by professionals from both health and education. We received data from 191 (54%) of the 473 health professionals contacted. Of the 434 education professionals contacted, 295 (72%) provided data.

Prevalence
We received over 26 000 ascertainment forms. After we eliminated duplicate notifications the number ascertained was 17 160 individual children. We calculated prevalence from observed counts and from counts adjusted by capture-recapture (figure). Prevalence declined for children in the oldest two cohorts (1981 and 1980), who were aged from 16 to 18 years when the ascertainment was conducted. Some would have left school and not been included in the education list; some would have transferred from paediatric to adult hearing services. Both effects violate a requirement for capture-recapture to be valid. Hence these cohorts were excluded.

	Discussion

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The prevalence of permanent childhood hearing impairment rises over a wider age range and to a higher plateau than has been reported previously. Previous ascertainment studies have included fewer children and a narrower range of cohorts and hence could not map the rise in prevalence across birth cohorts with the precision displayed in the figure. The profile of the rise in prevalence with age has important implications for service delivery, which can be dealt with only when the variables underpinning the rise are understood. Three effects are likely to contribute.

Some children acquire impairment postnatallyImpairments that are acquired, as distinct from progressive or of late onset, account for 4-9% of overall prevalence ^{7 15-16} and 7% in the present study. Thus they explain only a small proportion of the rise.

Confirmation of impairment is delayed in some childrenDelayed confirmation of congenital cases may contribute to the rise, particularly for lesser degrees of impairment. ^{7 8 21} If universal neonatal hearing screening identified all congenital impairments the yield from screening would be close to the aggregate prevalence seen in the table. In the United Kingdom the yield of children with bilateral hearing impairment 40 dB HL per 1000 live births has been reported as only 1.18 (34/28 890)²¹ and 0.94 (24/25 609),²² giving an aggregate yield of 1.06 (95% confidence interval 0.84 to 1.44). This is close to the overall prevalence in the youngest cohort in our study, and the upper confidence limit is below the aggregate prevalence (table). Thus it is unlikely that delayed confirmation fully accounts for the unexplained portion of the rise.

Some inherited causes of hearing impairment manifest themselves only postnatallyMany of the dominant genes for deafness are associated with late onset progressive hearing impairment. ^{23 24} The protracted rise in the prevalence of severe and profound impairments (figure) is more compatible with the idea that some children have impairments of progressively increasing severity than with the alternative that many congenital cases with severe and profound impairments were not confirmed until several years after birth.

The implementation of universal neonatal hearing screening should result in a well documented screening history for all children. That information, together with the results of genetic investigations in children with a newly confirmed diagnosis of permanent hearing impairment, would permit the rising profile of prevalence with age to be confirmed prospectively and would allow us to unravel the relative contributions of the three effects to the rise.

Conclusions
In the United Kingdom the prevalence of confirmed cases of permanent childhood hearing impairment >40 dB HL has risen with age to a significantly higher plateau than previous studies have estimated. Assuming that the yield from universal neonatal hearing screening will remain close to 1.06 per 1000 live births, we estimate that for every 10 children with a permanent bilateral hearing impairment >40 dB HL detected another five to nine children (50-90%) would manifest such a hearing impairment by the age of 9 years. These additional children would comprise some with congenital impairments who either miss neonatal hearing screening or pass the screening despite having a hearing impairment, some who acquire an impairment postnatally, and others who manifest late onset or progressive impairments. Paediatric audiology and associated services will need the capacity and skills to identify and then confirm impairments in these children.

	Acknowledgments

We thank every professional who identified children and Mrs Margaret Eatough for facilitating the ascertainment in the education sector.

	Footnotes

Funding: Medical Research Council with additional funding from the National Lottery Charities Board through Defeating DeafnessThe Hearing Research Trust.

Conflict of interest: None declared.

	References

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1.	Conrad R. The deaf schoolchild: language and cognitive function. London: Harper and Row, 1979.
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5.	Mohr PE, Feldman JJ, Dunbar JL, McConkey-Robbins A, Niparko JK, Rittenhouse RK, et al. The societal costs of severe to profound hearing loss in the United States. Int J Technol Assess 2000; 16: 1120-1135[Medline].
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7.	Fortnum H, Davis A. Epidemiology of permanent childhood hearing impairment in Trent region, 1985-1993. Br J Audiol 1997; 31: 409-446[Medline].
8.	Van Naarden K, Decouflé P, Caldwell K. Prevalence and characteristics of children with serious hearing impairment in Metropolitan Atlanta. Pediatrics 1999; 103: 570-575[Abstract/Full Text].
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11.	Dalzell L, Orlando M, MacDonald M, Berg A, Bradley M, Cacace A, et al. The New York State universal newborn hearing screening demonstration project: ages of hearing loss identification, hearing aid fitting, and enrolment in early intervention. Ear Hearing 2000; 21: 118-130[Medline].
12.	Department of Health. Piloting the introduction of universal neonatal hearing screening in England. www.doh.gov.uk/uhnspilots/index.htm (accessed 11 Jan 2001).
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20.	British Society of Audiology. Recommendations for pure-tone audiometry. Br J Audiol 1988; 22: 123.
21.	Watkin PM, Baldwin M. Confirmation of deafness in infancy. Arch Dis Child 1999; 81: 380-389[Abstract/Full Text].
22.	Kennedy CR. Controlled trial of universal neonatal screening for early identification of permanent childhood hearing impairment: coverage, positive predictive value, effect on mothers and incremental yield. Wessex Universal Neonatal Screening Trial Group. Acta Paediatr Suppl 1999; 88: 73-75[Medline].
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(Accepted 25 May 2001)

Commentary: Universal newborn hearing screening: implications for coordinating and developing services for deaf and hearing impaired children

Adrian Davis, head of epidemiology, public health and clinical sections, ^a Christine Yoshinaga-Itano, professor, ^b Sally Hind, developmental psychologist. ^a

^a Public Health and Clinical Section, MRC Institute of Hearing Research, University Park, Nottingham NG7 2RD, ^b Department of Speech, Language, and Hearing Sciences, University of Colorado, Boulder 80309-0409, Colorado, USA

Correspondence to: A Davis Adrian{at}ihr.mrc.ac.uk

The prevalence of permanent childhood hearing impairment of 40 dB HL or greater, and the probability that late onset and progressive hearing impairment may be more prevalent than previously indicated, has been discussed by Fortnum et al in their paper. There is no estimate available of the number of children with "mild" (20-40 dB HL) bilateral permanent impairment or those with unilateral impairment, but current programmes that screen for hearing problems in the newborn in the United States suggest that such impairment, identified by screening at birth, is at least as prevalent.¹

Screening hearing in newborns has been shown to be efficient² and cost effective,³ with a sensitivity in the range of 80-90%, a false positive rate of <2% ^{4 5} and a positive predictive value of 17%. The proposed costs of such screening in the United Kingdom are much lower than the costs of the current infant distraction screen test,⁸ and the cost per child identified as having bilateral permanent hearing impairment is considerably less. There is little evidence that screening all newborns for hearing raises anxiety among mothers.⁶

The benefits of universal newborn hearing screening for children with permanent hearing impairment are that early identification is associated with better expressive and receptive language, speech, and social and emotional development. Children who are identified before the age of 6 months show substantial benefit in the first five years of life, and there is some evidence that earlier enrolment in intervention programmes is associated with better outcomes.⁷ A higher level of expressive language in young children is linked with levels of parental stress and better attachment as measured by emotional availability. ^{8 9} However, if early identification and intervention is not handled well at the service level, it can generate anxiety and grief and bring about negative outcomes for the family.¹⁰

The Department of Health has started a universal newborn hearing screening programme in England, beginning with a pilot implementation with a hospital or clinic based protocol in 17 areas and a community based protocol in three areas. Concerns over the quality of services for the assessment of children's hearing for those referred from screening and of early intervention programmes for parents and their children who have a confirmed permanent hearing impairment have been raised. Family Friendly Hearing Services are being developed that have three main characteristics. Firstly, service provision by all professional sectors in a positive family friendly culture should encourage "seamless" collaboration, responsiveness that meets the family's real needs, and provision of appropriate information between all agencies and for parents that enables families to make informed choices about services for their children. Secondly, paediatric audiology should exceed a minimum standard in terms of quality and accessibility. Thirdly, there must be a culture of service evaluation, including peer review, with an element of feedback from parents and their children with impaired hearing. Data from screening and assessments will be kept nationally on a database integrated with other child services. This will facilitate the monitoring of later development of permanent childhood hearing impairment and the effectiveness of the screening programme.

The implementation team will rigorously assess access to and quality of health and social care for these families, and outcomes of the programme will be evaluated. Coordination of these services and support options are key factors in the success of the programme, and availability of the range of options would be severely restricted by a lack of appropriately trained staff and resources. The aim is to detect bilateral moderate to profound congenital permanent childhood hearing impairment to enable high quality parent-child intervention services.

The advent of a national newborn hearing screening programme creates the opportunity to help these children to develop their true potential, provided that the training, resources, and coordination are made available. We will need to monitor the outcomes of the children at different ages to enhance the evidence base concerning the most effective health, educational, and social interventions. There continues to be a need to develop and implement more effective screening and case finding for school aged children (4-16 years) with acquired and late onset hearing impairments that may negatively affect their behaviour and educational achievement.

	Footnotes

The full version of this paper appears on the BMJ's website

	References

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2.	Davis A, Bamford J, Stevens J. Performance of neonatal and infant hearing screens: sensitivity and specificity. Br J Audiol 2001; 35: 3-15[Medline].
3.	Stevens JC, Hall DM, Davis A, Davies CM, Dixon S. The costs of early hearing screening in England and Wales. Arch Dis Child 1998; 78: 14-19[Abstract/Full Text].
4.	Yoshinaga-Itano C, Coulter D, Thomson V. The Colorado newborn hearing screening project: effects on speech and language development for children with hearing loss. J Perinatol 2000; 20: S132-S137[Medline].
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8.	Pressman L, Pipp-Siegel S, Yoshinaga-Itano C, Deas A. Maternal sensitivity predicts language gain in preschool children who are deaf and hard-of-hearing. J Deaf Studies Deaf Education 1999; 4: 294-304.
9.	Pressman L, Pipp-Siegel S, Yoshinaga-Itano C, Kubicek L, Emde RN. A comparison of the links between emotional availability and language gain in young children with and without hearing loss. Volta Review 2000; 100: 251-277.
10.	Hind S, Davis A. Outcomes for children with permanent hearing impairment. In: Seewald R, ed. A sound foundation through early amplification. Proceedings of the International Conference sponsored by Phonak Oct 1998, Chicago, Illinois, US. Staefa, Staefa, Switzerland: Phonak AG, 2000:199-212.