Early Hearing and Communication Development

 

Chapter III: Burden of the Target Disorder

Target Disorder

Author: Dr. Martyn Hyde

The "burden" of the target disorder is a term that refers to the overall set of negative consequences that may be a result of its occurrence. The target disorder is most commonly (albeit, not necessarily) defined in terms of parameters of hearing impairment, such as severity, laterality, type and time at expression. The burden of the disorder reflects its negative impact on the individual child and family, and upon society as a whole. The latter aspect of burden is governed primarily by the number of affected children and families (prevalence of the disorder) and by its cultural and socioeconomic effects.

The impact of a given hearing impairment on a particular child and family is widely believed to depend on many variables, and especially upon when the impairment is identified and what services are engaged to address it. These services may include, but are not limited to: family information and counseling; psychological, social and economic supports; assistive technologies such as personal amplification; other assistive devices; and cochlear implants. Instruction aimed at development of communication skills may include manual, oral or combined approaches. The effectiveness of all these services will depend on their nature, timeliness, accessibility, quality and acceptability. There is always some particular pattern of events related to service performance (or the lack of it), and so the impact of the target disorder must be considered as intimately connected to the current service pattern and its effects. For example, if it is assumed that high quality services are effective, then if services were inaccessible, inappropriate or of poor quality, the negative impact of a given spectrum of the target disorder would be increased.

For the purposes of this document, the primary focus in target disorder definition is upon hearing impairment that is congenital and is stable or progressive. This is referred to as permanent childhood hearing impairment (PCHI). Etiologically, most such impairment involves cochlear dysfunction and is medically irremediable. Structural conductive impairments which may arise from maldevelopment of the external or middle ears are usually included because they impose long-standing dysfunction, unless treated surgically.

Prevalence of Permanent Childhood Hearing Impairment

Author: Dr. Martyn Hyde

The prevalence of permanent childhood hearing impairment (PCHI) in the age range 0-5 years is reviewed in this section. Most PCHI is sensorineural but structural conductive impairment (e.g., ear canal atresia) is included. Congenital impairment is defined as impairment recognized at birth or believed to have been present since birth. Late-onset impairment is impairment not present at birth and that cannot be attributed to an exogenous cause. Acquired impairment is impairment not present at birth and for which an exogenous cause can be identified. Progressive impairment is impairment that increases over time, regardless of its point of initial manifestation.¹

These terms must be interpreted with great caution, because most datasets were obtained in the absence of comprehensive, valid and accurate hearing assessment in the neonate and infant. Thus, with the possible exception of recent, high quality, universal newborn hearing screening (UNHS) studies, prevalence of strictly congenital PCHI probably has been overestimated, and that of late-onset, acquired and progressive impairment underestimated.

Variation and Bias in Prevalence Estimates

There is large variation in reported prevalence. Major sources of variation include: random sampling error; the definition of the target disorder; the completeness and accuracy of the determination of hearing status; the definition of the target population; the methods by which that population is sampled; the age of the study population; demographic, cultural and behavioural factors; and the availability and quality of perinatal care.

Ascertainment Studies

Ascertainment studies involve case identification through notification systems or database surveys. Negative bias due to under-ascertainment is a concern, as are geographic consistency of case capture and the stability over time of the case-finding system, of the underlying population epidemiology, and of the hearing impairment measurement practices.

By far the most comprehensive ascertainment-based prevalence report to date is due to Fortnum et al.¹ This was a well-executed ascertainment study of a 15-year birth cohort in the U.K. (1980-1995), with 17,160 cases ascertained. The target disorder was PCHI of greater than 40 dBHL average over 0.5, 1, 2 and 4 kHz in the better ear. Adjusted prevalence was reported as 1.07 per 1,000 live births at 3 years and 2.05 per 1,000 live births at more than 9 years of age. Possible causes of the increase with age include progressive or delayed-onset PCHI, delayed confirmation of congenital PCHI, and acquired PCHI. There is insufficient information to resolve the relative contributions of these factors, all of which may contribute significantly.

The prevalence findings are reasonably consistent with those from other authors. Studies with substantial sample sizes were reviewed. They revealed significant effects of the target disorder criterion, as well as differences across demographic subgroups. The estimated congenital prevalence of moderate or greater hearing impairment for the accepted studies ranges from 0.09 to 1.16 per 1,000 live births. It should be noted that all these studies reported on hearing levels in the better ear, that is, on bilateral impairment. Also, they targeted average hearing levels over a frequency range. This represents a conservative approach to the definition of target PCHI.

Prevalence Estimates from Universal Newborn Hearing Screening Programs

Prospective prevalence estimates may be obtained from reports of large newborn hearing screening programs. Because only newborn screening referrals are followed up, UNHS programs are not cohort studies and they provide information exclusively about truly congenital PCHI. Other important limitations of UNHS studies are that prevalence estimates have large confidence intervals (due to the limited number of cases in typical study samples), and they may be biased due to incomplete screening coverage and follow-up or due to study-specific characteristics. Also, there is variation in target disorder definition, in the sensitivity of screening methods used, and in the accuracy and timing of hearing assessments.

The highest quality UNHS data was provided by the New York State UNHS demonstration project.² For this program, the adjusted prevalence of hearing impairment greater than 20 dB in either ear was 2.8 per 1,000 live births. For five acceptable program reports addressing at least mild, congenital PCHI in any ear (unilateral or bilateral impairment), the median unadjusted prevalence was approximately 2.2 per 1,000 live births. This value is biased negatively by incomplete follow-up. The adjusted median estimate accounting for children lost to follow-up is 3.2 per 1,000 live births.

The contrast between the UNHS estimates of congenital prevalence for PCHI criteria of better-ear >40 dBHL (Wessex and East London, average 1.06/1,000) versus the adjusted any-ear >20 dBHL value of 3.2 per 1,000 live births suggests that the prevalence of hearing impairment may triple if the severity threshold is changed from 40 dB to 20 dB and if unilateral impairment is included. However, there may be interactions among these variables, and the fact that common screening protocols will under-detect mild hearing impairments means that the true increase in prevalence may be greater than three-fold. At present, there are insufficient data to quantify prevalence in detail as a function of these three major variables.

Prevalence in At-Risk Groups

The U.S. Joint Committee on Infant Hearing (JCIH) has published a series of guidelines for risk indicators that predispose newborns and infants to congenital, progressive, late-onset or acquired PCHI.³

Prevalence estimates for PCHI in at-risk groups vary greatly. As well as the sources of variation noted earlier, risk determination itself adds further variability. Reported proportions of infants at risk vary with the risk indicator set and range from 3% to over 15%.

Accurate risk assignment requires that indicators be defined consistently and quantitatively, and that risk information be properly recorded, accessible and diligently sought. In practice, these conditions are never satisfied for all indicators. There is evidence that accurate determination of risk is time-consuming and far from straightforward. Also, geographic variations and advances over time in perinatal care quality may change both the prevalence of risk and its predictive value for impairment.

With respect to ascertainment studies, the overall prevalence of congenital impairment in the Trent study⁴ was 1.12 per 1,000 live births for a 40 dB better-ear criterion; it increased from 0.54 per 1,000 in low-risk children to 3.2 per 1,000 for neonatal intensive care unit (NICU) graduates, and 7.6 per 1,000 live births for children with a family history.

In the New York State study,² the adjusted prevalences for mild or greater impairments in any ear were 1.2 per 1,000 and 11.2 per 1,000 live births in the well-baby nursery (WBN) and NICU groups, respectively; for bilateral impairment only, these values were more than halved, to 0.49 and 4.8/1,000. Vohr et al.⁵ obtained similar values of 1.27 and 9.8/1,000, for the WBN and NICU, respectively. However, not all NICU graduates are at increased risk. The proportion may be as low as 60%, so estimates based on NICU attendance underestimate true at-risk prevalence. Also, not all WBN graduates are free from risk, so the prevalence of low-risk status may be overestimated. It is likely that these concepts of risk have been confounded in the literature, which may have contributed to bias and substantial variation among reports. It is also probable that diligent pursuit of risk information would frequently reveal substantial underestimation of the true proportion at risk.

In a high quality, prospective cohort study,⁶ the prevalence of PCHI in the NICU was 1.5%. Of the 56 infants with PCHI, 30 (over half) had bilateral impairment. Other studies have yielded prevalence estimates as high as 4%, though many studies have significant methodologic limitations, especially relating to the timing and accuracy of audiologic assessment.

Key References

1. Fortnum HM, Summerfield AQ, Marshall DH, et al. Prevalence of permanent childhood hearing impairment in the United Kingdom and implications for universal neonatal hearing screening: questionnaire based ascertainment study. Brit Med J. 2001 Sep 8; 323(7312):536-40.
2. Prieve B, Dalzell L, Berg A, et al. The New York State universal newborn hearing screening demonstration project: outpatient outcome measures. Ear Hearing. 2000 Apr; 21(2):104-17.
3. Joint Committee on Infant Hearing [homepage on the Internet]. Year 2000 Position Statement: Principles and Guidelines for Early Hearing Detection and Intervention Programs. 2000 Jun. Available from: <http://www.infanthearing.org/jcih/>.
4. Fortnum H, Davis A. Epidemiology of permanent childhood hearing impairment in Trent Region, 1985-1993. Brit J Audiol. 1997 Dec;31(6):409-46.
5. Vohr BR, Carty LM, Moore PE, Letourneau K. The Rhode Island Hearing Assessment Program: experience with statewide hearing screening (1993-1996). J Pediatr. 1998;133:353-7.
6. Vohr BR, Widen JE, Cone-Wesson B, et al. Identification of neonatal hearing impairment: characteristics of infants in the neonatal intensive care unit and well-baby nursery. Ear Hearing. 2000 Oct;21(5):373-82.

Temporal Pattern of Permanent Childhood Hearing Impairment Detection in the Absence of Universal Newborn Hearing Screening

Author: Dr. Andrée Durieux-Smith

Studies relating to the pattern of detection of permanent childhood hearing impairment (PCHI) in the absence of universal newborn hearing screening (UNHS) have been critically reviewed and are summarized here. The target disorder for the critical review is defined as a PCHI of 40 dBHL (0.5, 1 or 2 kHz) in the better ear. The review is restricted to the diagnosis of presumed congenital hearing impairment. Only literature published in 1990 or later is included, because it is felt that, before that time, technology may not have been available to accurately diagnose PCHI in infancy.

Studies on the age of diagnosis or confirmation of PCHI in the absence of UNHS fall into different categories. These include studies on the age of diagnosis in the absence of any screening activities, in the presence of some screening activities, and studies that have included some populations screened during the neonatal period as well as unscreened populations.

Studies on the age of diagnosis in the absence of any screening activities report on data collected by retrospective chart reviews and analyses of existing databases^1-3, by parental questionnaires⁴ and by a combination of methods.⁵ The results indicate that, on average, the age at diagnosis of PCHI in children exceeds 12-18 months; that there is an inverse relationship between degree of hearing impairment and age of identification; and that children with risk factors, additional medical or handicapping conditions are diagnosed earlier than children without such conditions.

In some studies, the age at PCHI confirmation is reported in the presence of some behavioural screening at age 7-9 months. Such studies have been done in the United Kingdom,^6-8 Australia,^9,10 Finland¹¹ and Denmark.¹² In some cases, the screening at 7-9 months was replaced by a vigilance program that includes questions for parents and professionals.^6,7 Some of these studies also report some screening of high-risk neonates,^6-10 although no data are provided separately for the screened infants. Also included in this category of studies are those that have used a high-risk birth certificate registry.¹³ The results of all these studies are not very different than those reported in the absence of screening. The mean or median ages at diagnosis exceed 12 months; children with risk factors are identified earlier than those without and there is an inverse relationship between degree of hearing impairment and age at diagnosis. Finally, studies in which some targeted newborn hearing screening was taking place report a lowering of the age at diagnosis for the entire birth cohort during that time. Studies that have compared different birth cohorts report a lowering of age at diagnosis over time.¹² This indicates an increased awareness of hearing impairment in children, most likely by physicians and health care professionals.

Studies comparing neonatally screened and unscreened populations include results for UNHS versus unscreened populations^14,15 and for targeted screened (high-risk and/or neonatal intensive care unit (NICU) babies) and non-screened populations.^16,17 Results of these studies clearly show that the age of diagnosis of babies with a PCHI is significantly lower for those identified through screening than for those identified through the traditional medical referral route.

The results of three major studies on the outcome of UNHS programs^18-20 are presented for comparison. These results indicate that, in the presence of UNHS, the median age of diagnosis for children with PCHI ranges from 2.1 months18 to 3 months.¹⁹ In addition, studies that have been collecting data over several years indicate an improvement in the ages of diagnosis over time because of experience in the development and refinement of programs.²⁰

Relationship Between Severity of Hearing Impairment and Pattern of Detection

Information on the temporal pattern of detection in relation to the degree of hearing impairment severity was extracted from most of the articles already reviewed in which age at diagnosis for children in different types of health systems were presented. The results of these studies indicate that in the absence of UNHS, children with profound hearing impairments are identified sooner than children with lesser degrees of impairment, although rarely before 12 months of age. Children with moderate hearing impairments are identified between 20 and 42 months of age.^1-4,16 For children identified through UNHS, there is no significant difference in the ages at diagnosis for children with different degrees of hearing impairment.

Conclusions

• The prevalence of permanent childhood hearing impairment (PCHI) is about 1/1,000 live births in infancy if one uses 40 dBHL in the better ear as the cut-off. This rate increases to about 2/1,000 live births over the first decade of life.
• In the absence of systematic screening, the detection, confirmation, diagnosis and management of hearing impairment are significantly delayed.
• With universal newborn hearing screening (UNHS), the median age of diagnosis is less than 3 months.

Key References

1. Van Naarden K, Decoufle P, Caldwell K. Prevalence and characteristics of children with serious hearing impairment in Metropolitan Atlanta, 1991-1993. Pediatrics. 1999;103:570-5.
2. Strong CJ, Clark T, Walden B. The relationship of hearing-loss severity to demographic, age, treatment, and intervention-effectiveness variables. Ear Hearing. 1994;15(2):126-37.
3. Mace AL, Wallace K, Whan M, et al. Relevant factors in the identification of hearing loss. Ear Hearing. 1991;12(4):287-93.
4. Harrison M, Roush J. Age of suspicion, identification, and intervention for infants and young children with hearing loss: a national study. Ear Hearing. 1996;17(1):55-62.
5. Stein LK, Jabaley T, Spitz R, et al. The hearing-impaired infant: patterns of identification and habilitation revisited. Ear Hearing. 1990;11(3):201-5.
6. Sutton GJ, Scanlon P. Health visitor screening versus vigilance: outcomes of programmes for detecting permanent childhood hearing loss in west Berkshire. Brit J Audiol. 1999;33(3):145-56.
7. Fonseca S, Forsyth H, Grigor J, et al. Identification of permanent hearing loss in children: are the targets for outcome measures attainable? Brit J Audiol. 1999;33(3),135-43.
8. Fortnum H, Davis A. Epidemiology of permanent childhood hearing impairment in Trent Region, 1985-1993. Brit J Audiol. 1997 Dec;31(6):409-46.
9. Russ SA, Rickards F, Poulakis Z, et al. Six year effectiveness of a population based two tier infant hearing screening programme. Arch Dis Child. 2002 Apr;86(4):245-50.
10. Robertson C, Aldridge S, Jarman F, et al. Late diagnosis of congenital sensorineural hearing impairment: why are detection methods failing? Arch Dis Child. 1995;72(1):11-5.
11. Vartiainen E, Karjalainen S. Congenital and early-onset bilateral hearing impairment in children: the delay in detection. J Laryngol Otol. 1997;111(11):1018-21.
12. Parving A, Jensen J. Prevalence of permanent childhood hearing impairment - its role in audit of local paediatric hearing health services. J Audiol Med. 1998;7(2):100-8.
13. Mauk GW, White K, Mortensen L, et al. The effectiveness of screening programs based on high-risk characteristics in early identification of hearing impairment. Ear Hearing. 1991;12(5):312-9.
14. Nekahm D, Weichbold V, Welzl-Mueller K, et al. Improvement in early detection of congenital hearing impairment due to universal newborn hearing screening. Int J Pediatr Otorhi. 2001;59(1):23-8.
15. Wessex Universal Neonatal Hearing Screening Trial Group. Controlled trial of universal neonatal screening for early identification of permanent childhood hearing impairment. Lancet. 1998 Dec 19-26;352(9145):1957-64.
16. Durieux-Smith A, Whittingham J. The rationale for neonatal hearing screening. J Speech Lang Pathol Audiol. 2000 Jun;24:59-67.
17. Watkin PM, Baldwin M, McEnery G. Neonatal at risk screening and the identification of deafness. Arch Dis Child. 1991;66(10 Spec. No.):1130-5.
18. Mehl AL, Thomson V. The Colorado newborn hearing screening project, 1992-1999: on the threshold of effective population-based newborn hearing screening. Pediatrics. 2002 Jan;109(1):E7.
19. Dalzell L, Orlando M, MacDonald M, et al. The New York State universal newborn hearing screening demonstration project: ages of hearing loss identification, hearing aid fitting, and enrollment in early intervention. Ear Hearing. 2000 Apr;21(2):118-30.
20. Vohr BR, Carty LM, Moore PE, Letourneau K. The Rhode Island Hearing Assessment Program: experience with statewide hearing screening (1993-1996). J Pediatr. 1998;133:353-7.

Additional References

Cone-Wesson B, Vohr BR, Sininger YS, et al. Identification of neonatal hearing impairment: infants with hearing loss. Ear Hearing. 2000 Oct;21(5):488-507.

Davis A, Bamford J, Wilson I, et al. A critical review of the role of neonatal hearing screening in the detection of congenital hearing impairment. Health Technol Assess. 1997;1(10):i-iv,1-176. Review.

Davis AC, Parving A. Towards appropriate epidemiological data on childhood hearing disability: a comparative European study of birth cohorts 1982-88. J Audiol Med. 1994;3:35-47.

Finitzo T, Albright K, O'Neal J. The newborn with hearing loss: detection in the nursery. Pediatrics. 1998 Dec;102(6):1452-60.

Galambos R, Wilson MJ, Silva PD. Identifying hearing loss in the intensive care nursery: a 20-year summary. J Am Acad Audiol. 1994 Mar;5(3):151-62.

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 Dec;88(432):73-5.

Maki-Torkko EM, Lindholm PK, Vayrynen MR, et al. Epidemiology of moderate to profound childhood hearing impairments in northern Finland: any changes in ten years? Scand Audiol. 1998;27:95-103.

Mehl AL, Thomson V. Newborn hearing screening: the great omission. Pediatrics. 1998 Jan;101(1):E4.

Stapells D, Oates P. Estimation of the pure-tone audiogram by the auditory brainstem response: a review. Audiol Neuro-Otol. 1997 Sept-Oct;2(5):257-80.

Stein LK. Factors influencing the efficacy of universal newborn hearing screening. Pediatr Clin N Am. 1999 Feb;46(1):95-105.

Thompson DC, McPhillips H, Davis RL, et al. Universal Newborn Hearing Screening. JAMA. 2001 Oct;286:2000-10.

Widen JE, Folsom RC, Cone-Wesson B, et al. Identification of neonatal hearing impairment: hearing status at 8 to 12 months corrected age using a visual reinforcement audiometry protocol. Ear Hearing. 2000 Oct;21(5):471-87.

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