Fitzpatrick, Elizabeth M.1,2; Whittingham, JoAnne2; Durieux-Smith, Andrée1,2
Permanent hearing loss, which affects 2 to 4 per 1000 children (Fortnum et al. 2001; Russ et al. 2003; Watkin & Baldwin 2011), has gained increasing attention since the introduction of universal newborn hearing screening (UNHS). The negative effects of bilateral hearing loss of moderate degrees and greater (>40 dB HL) on spoken language have been well documented (Kennedy et al. 2006; Nelson et al. 2008; Ching et al. 2010; Sininger et al. 2010; Fitzpatrick et al. 2011). Consequently, there is an international consensus regarding the importance of acoustic amplification and interventions to mitigate these effects (Nelson et al. 2008; Bagatto et al. 2010; King 2010). However, practices for children identified with mild bilateral hearing loss or unilateral hearing loss (MBUHL) are much less certain (McKay et al. 2008; Tharpe 2008; Fitzpatrick et al. 2010).
Historically, late diagnosis at 4 to 5 years of age of both mild bilateral hearing loss (MBHL) and unilateral hearing loss (UHL) was common (Watkin 1991; Durieux-Smith et al. 2008; Tharpe 2008; Fitzpatrick et al. 2010), but with newborn hearing screening and particularly since UNHS, these types of hearing loss can be identified in early childhood (Yoshinaga-Itano et al. 2008; Watkin & Baldwin 2011). While some UNHS programs include MBUHL in their target population (Hyde 2005), others aim to identify moderate or greater hearing loss due to the uncertainty around the benefit of early intervention and the technical difficulties in identifying very mild loss (Russ et al. 2002; Bamford et al. 2005). For these reasons and due to variations in definitions, the prevalence of MBUHL has been difficult to establish, with best estimates ranging from 0.4 to 1.3 per 1000 newborns (Watkin & Baldwin 1999; Johnson et al. 2005). Studies of school-aged children also show considerable variability, ranging from 0.88% with slight/mild bilateral loss in 6581 Australian children (Wake & Poulakis 2004) to 2.4% (MBHL) and 3.0% (UHL) in 1218 U.S. children (Bess et al. 1998). Recent data from the United Kingdom for a newborn screening cohort of 35,668 showed a prevalence of 3.64 children with permanent hearing loss per 1000 children in the first year of school. Hearing loss of moderate or worse degree was reported in 1.51/1000, leaving 2.14/1000 (58.6%) with MBHL (1.2/100) or UHL (0.81/1000) (Watkin & Baldwin 2011).
Until the 1980s, relatively little attention was accorded to “minimal losses” as the effects on development were thought to be negligible (Tharpe 2008; Porter & Bess 2011). However, there is considerable literature documenting that children with MBUHL experience difficulties at school age, including poor speech understanding in noise, and localization difficulties (Bess & Tharpe 1984; Bess et al. 1986, 1998; Porter & Bess 2011). For some late-identified children, there is evidence of negative effects on language, academic, and psychosocial development (Bess et al. 1998; Hick & Tharpe 2002; Most 2004; Wake et al. 2004). A recent study (Lieu et al. 2010) supported these earlier findings and showed that children with UHL had poorer language scores than their siblings and were more likely to have an individualized education plan and speech-language services. Taken together, these reports indicate that children with MBUHL are at risk for adverse educational outcomes (Tharpe 2008; Porter & Bess 2011). Treatment approaches for MBUHL appear to range from “watchful waiting” to specific management with hearing devices and speech-language services. Relatively little information is available about the impact of early-identified MBUHL on children’s development or to guide clinical decision making regarding interventions. Yoshinaga-Itano et al. (2008) suggested that despite early identification, approximately one third of these children will experience delays in language development.
In a previous study, we documented that MBUHL accounted for more than 40% of children identified in a pediatric audiology clinic (Fitzpatrick et al. 2010). In the absence of screening, limited information has been available about progression of hearing loss, one of the reasons put forth to justify targeting MBHL in screening initiatives (Hyde 2005). Since 2002, a province-wide comprehensive UNHS program that includes screening, high-risk infant surveillance, diagnostic audiologic evaluation, and family support services has been implemented in the province of Ontario. Provincial protocols include a multistage screening process, which involves automated otoacoustic emissions in the well-baby nursery followed by automated auditory brainstem response testing (AABR) for automated otoacoustic emission refer outcomes. Infants at high risk for permanent hearing loss (e.g., in the neonatal intensive care unit [NICU]) undergo AABR screening (Hyde 2005). Screening programs such as the Ontario program that include MBUHL within the case definition have facilitated collection of prospective data and closer examination of the clinical characteristics of these children. Such information may have value for clinical decision making and parent counseling for this new clinical population.
This study had four primary objectives: (1) to examine the proportion of children with MBUHL in a clinical population; (2), to describe the clinical characteristics of children with MBUHL; (3) to document practices related to identification and amplification; and (4) to examine the factors affecting clinical recommendations. In summary, we report 20-year data from one Canadian region before and after the implementation of a UNHS program.
MATERIALS AND METHODS
Clinical characteristics were collected prospectively as part of a research database maintained for all children identified with permanent hearing loss from 1990 to 2010 at the Children’s Hospital of Eastern Ontario in Ottawa, Canada, a publicly funded pediatric teaching hospital. Clinical characteristics documented for all children included child-specific (e.g., sex, screening status, NICU status) and hearing loss-specific information (e.g., age of confirmation, type of loss, etiology, audiometric thresholds, age and type of amplification, changes in hearing loss or hearing technology). For this study, these details were extracted from the database, and details of the use of amplification were collected retrospectively via detailed medical chart review. Since 1975 the hospital has delivered audiologic services to an estimated 95% or more of children with hearing loss in a catchment area of 1 million. Since the implementation of province-wide UNHS in 2002, the hospital has been the designated diagnostic center for the approximately 12,000 infants screened in the region and consequently provides audiologic assessments for all children who receive a refer result from screening tests. Under provincial UNHS protocols, well babies undergo two screens and babies in the NICU have one AABR screen before referral to diagnostic audiology. Consistent with provincial screening protocols, the AABR screen is conducted using click stimuli, and the click level is equivalent to 35 dBnHL. In addition, children with known risk factors for hearing loss are placed on a surveillance list. Thirty-five to 40 children with permanent hearing loss ranging from mild to profound degrees are identified annually in the region. Before UNHS, children were referred through physicians or through a hospital-managed high-risk screening program in place from 1981 to 2001.
There is considerable variation in the definition of MBUHL. For the purposes of this study the working definition proposed by the National Workshop on Mild Bilateral and Unilateral Hearing Loss (2005) was adopted. Study criteria included all children aged 0 to 18 years identified with mild bilateral (better ear) or unilateral loss. Children with bilateral loss were divided into two subgroups, mild in the better ear (average hearing at 0.5, 1, and 2K Hz) and mild high-frequency hearing loss (2 or more frequencies above 2K Hz). Children with known acquired hearing loss associated with etiologies such as meningitis or ototoxicity were excluded. This study was approved by the institutional review boards of the Children’s Hospital of Eastern Ontario and the University of Ottawa.
As noted, clinical characteristics were collected at diagnosis of hearing loss and were updated at return visits to audiology to document changes in hearing status and other areas (e.g., etiology) as information became available. These data and details related to recommendations for and use of amplification were entered into a study-specific data form.
Statistical analysis was performed using SPSS Version 19 (IBM Corp., Armonk, NY). The primary outcome of interest was the number of children with MBUHL pre- and post-UNHS and their diagnostic history. Secondary outcomes included the number of children with recommendations for and uptake of amplification. Baseline characteristics were summarized using descriptive statistics and included means and standard deviations or medians and interquartile ranges (IQRs) as appropriate, and frequency counts. Continuous characteristics and outcomes normally distributed were compared between the two study periods using a Student’s t test. Otherwise a nonparametric approach (Mann–Whitney U test) was applied. Differences between groups for categorical variables were assessed using χ2 test or Fisher’s exact test. Logistic regression analysis was conducted to examine the association between amplification decisions and age at confirmation of hearing loss, severity of hearing loss in the worse ear, and severity in the better ear (for the mild bilateral group).
Proportion of Children Identified
A total of 864 children were identified with permanent hearing loss from 1990 to 2010. After excluding 41 children with known acquired losses, 823 children were entered in the study. Figure 1 shows the selection of study participants, 585 children (71.1%) were identified pre-UNHS (1990 to 2001) and 238 (28.9%) post-UNHS (2002 to 2010). During the 20-year time frame, 46.3% (n = 381) children presented with MBUHL with no significant difference between the two periods, (47.6% pre-UNHS; 42.9% post-UNHS), (p = 0.207). After removing lost-to-follow-up patients, 235 pre-UNHS and all 102 post-UNHS charts were available for further analyses.
Age of Confirmation of Hearing Loss
The 235 pre-UNHS children were confirmed at a median age of 5.0 years (IQR, 3.6 to 7.0) (Table 1). According to hospital policy, children were seen for an evaluation in the audiology clinic through physician referral. The pre-UNHS group was primarily a nonscreened group with only 29 (12.3%) exposed to targeted high-risk screening and only 20 with hearing loss confirmed by the age of 1 year. Figure 2 shows the distribution of children in each diagnostic period by screening status. As shown, post-UNHS children were confirmed much earlier than pre-UNHS children (p < 0.001) at an overall median age of 0.8 years (IQR, 0.3 to 2.3). A smaller percentage of MBUHL in the UNHS period (42.9% post-UNHS versus 47.6% pre-UNHS) may reflect that fact that late-onset hearing loss has not yet been confirmed in this younger group of children.
Figure 3 provides details on the 102 post-UNHS children. Of 82 screened children, 67.1% (55) were referred for audiologic assessment after receiving a refer result from screening test and were identified at a median age of 0.3 years (IQR, 0.2 to 0.6). Age of confirmation of permanent hearing loss was highly variable in these 55 children with congenital or early onset loss referred from screening. Permanent hearing loss was confirmed for 69.1% (38) by 6 months and an additional 18.2% (10) by 1 year of age. Late confirmation (>12 months) for 7 of the 55 children was due to parental follow-up issues (n = 4), inconclusive test results (n = 2), and medical issues (n = 1). Another 32.9% (27) who initially passed screening or had normal hearing at first assessment (12 of the 27) presented with delayed onset loss, which was confirmed at a median age of 2.0 (IQR, 1.0 to 4.7 years); 16 of these had high-risk factors for hearing loss. These children were classified as having delayed onset rather than acquired hearing loss due to a normal screen or a first diagnostic assessment within normal limits and no history of any identifiable exogenous cause (e.g., meningitis). An additional 20 children not screened (see Fig. 3 for reasons) were identified at a median age of 3.3 years (IQR, 1.0 to 4.7 years).
Clinical characteristics are provided in Table 1, where children are categorized into three groups: (1) MBHL averaged across three frequencies (n = 236), (2) mild high-frequency bilateral loss (MHFBHL; n = 39), and (3) UHL (n = 62). Etiology was unknown for 52.2% (176 of 337) of all children and a similar pattern was observed across all groups. Syndromic hearing loss was reported for 19.0% of all children (64 of 337), accounting for 39.8% of known etiologies (64 of 161). Forty-five children (without syndromes) were NICU graduates, accounting for 28.0% of the 161 with known etiologies. Of the 161 known etiologies, family history or genetic hearing loss (documented through a report of genetics testing in the medical chart) explained another 19.9%, and hearing loss associated with ear, nose, and throat (ENT) anomalies accounted for 12.4%. Six of 32 children with genetic causes were identified with GJB2 mutations. It is important to note that before UNHS, a specific genetics testing protocol was not in place, and etiology workup was at the discretion of the attending ENT physician. Specifically for the 62 children with UHL, almost one third (9 of 30) with known etiologies had documented ENT anomalies, of which 5 children presented with enlarged vestibular aqueduct syndrome, which has commonly been associated with hearing loss. One child with UHL had congenital cytomegalovirus (CMV), a major cause of nongenetic hearing loss (Nance et al. 2006; Misono et al. 2011). Routine screening for neonatal CMV infection was, however, not in place during the study period.
Severity and Progression of Hearing Loss
At initial assessment, 81.6% (275) of children presented with mild bilateral loss (based on better ear thresholds) and 18.4% (62) with unilateral loss. However, more than one third (37.8%) of children with bilateral loss and 58% (36) with unilateral loss had greater than mild hearing loss in the worse or impaired ear (Table 2). Permanent conductive loss was found in 11.9% children (40), typically due to structural malformations or permanent loss associated with syndromes (16 of 40).
Figure 4 details the initial severity and subsequent progression of hearing loss. Hearing was eventually documented as within normal limits for 6 of 337 children (1.8%). Of these, two children had Down’s syndrome, one had cerebral palsy, one had chronic middle ear problems and two were unexplained. In the MBHL group (n = 236), 23 showed improvement, 9 (3.8%) moving to MHFBHL and 14 (5.9%) to UHL. None of the 62 UHL children showed improvement in thresholds over time.
A total of 74 children (22.0%), some from each of the three hearing- loss categories, experienced deterioration in hearing, either in terms of laterality or audiometric thresholds (Fig. 4). Of the 74 children, 50 were classified with progressive loss (defined as 20 dB or greater deterioration in pure-tone average at 0.5, 1K, and 2K Hz). The other 24 children were reclassified to more severe categories based on deterioration (less than 20 dB) in thresholds. Specifically, in the group identified since the implementation of UNHS, for whom early screening and audiometric information were therefore available, 33 of 102 (32.4%) experienced deterioration, 26 of whom had more than 20 dB change in average hearing thresholds.
Examination of Clinical Practices
Overall, 51.3% (173 of 337) of children received a recommendation for amplification at identification (within 3 months) but practice patterns varied considerably (Fig. 5). Almost 60% with bilateral loss (58.5% of children with MBHL and 56.4% with MHFBHL) received initial recommendations compared with 21% (13 of 62) of UHL children. Further examination was conducted for the 236 children classified as MBHL based on better ear thresholds. Initial recommendations for amplification were not significantly different (p = 0.350) for children with mild loss in both ears (55.8% recommended for 138 children) and those with mild loss in the better ear (62.2% recommended for 98 children). Initial fitting practices did not vary significantly between the pre- and post-UNHS periods for MBHL (p = 0.107), MHFBHL (p = 1.00), or UHL (p = 0.093) groups. Although not statistically significant, overall, a slightly greater proportion of pre-UNHS children (54.5 versus 44% post-UNHS; p = 0.08) received amplification at identification.
Eventually 87.2% (294 of 337) of children received recommendations for amplification. Examination of time to recommendation showed that 22.8% (77) experienced more than 12 months’ delay with two thirds receiving recommendations from 2 to more than 6 years (n = 8) postdiagnosis. Similar practice patterns were noted in both study periods (Fig. 6). Amplification decisions for the 69.6% of post-UNHS group with amplification, varied over time with 44.1 % (45 of 102) receiving initial recommendations for amplification. A smaller group of children in the post-UNHS period (12 of 102) did not receive a recommendation for amplification until more than a year after diagnosis.
An examination of amplification decisions in relation to hearing-loss severity and age at confirmation was carried out using logistic regression analysis. Amplification decisions for children with MBHL were associated with older age at identification (odds ratio [OR] 1.24; 95% confidence interval [CI] 1.13 to 1.36) and greater severity of hearing loss in the better ear (OR 1.08; CI 1.04 to 1.12), but not with severity of hearing in the worse ear (OR 1.00; CI 0.98 to 1.01). In other words, after adjusting for severity of hearing loss, the odds of having amplification prescribed at initial confirmation were 24% higher for each additional year of increase in the age at confirmation of hearing loss. We further explored this association using age at confirmation as a dichotomous variable to divide the group according to preschool (0 to 4 years of age) and school age (>4 years). An OR of 3.63 (CI 2.10 to 6.27) indicated that children who were identified at school age were significantly more likely to be prescribed amplification. In addition, for every decibel of increase in hearing loss (pure-tone average), the odds of having amplification recommended at confirmation of hearing loss were 8% higher. In contrast, for UHL children, there was no association between amplification decisions and age of identification or severity of loss in the impaired ear. However, the small number of children in this group may have limited the power to determine any effects.
Figure 7 illustrates changes in amplification for 173 children with and 164 without initial recommendations for amplification. Generally, children fitted with amplification (93.6%) continued to have documented recommendations for amplification. Discontinued use of amplification was recommended for 11 cases including 3 children whose hearing loss resolved. Of 164 children without initial recommendations, 73.8% (121) eventually received a prescription, including 23 with progressive loss and 5 for whom amplification was later discontinued.
Uptake of amplification was examined for the 278 children with amplification recommendations at their most recent follow-up. The findings were based on audiologists’ chart documentation, which relied on parental report at the child’s audiology follow-up visit. A total of 70.2% (195) of children were reported to use amplification on a regular basis (documentation of consistent use both at home and school for 60.8% and consistent school use for 9.4%), leaving 29.8% classified as inconsistent/nonusers, lost to follow-up, or not following recommendations. There were no clear differences in amplification use between children with MBHL, MHFBHL, and UHL (p = 0.556).
This population-based study found that MBUHL accounted for 46.3% of childhood hearing loss. This proportion is somewhat lower than the 58.5% recently reported in a U.K. newborn screening cohort studied at school age (Watkin & Baldwin 2011), and may reflect that delayed onset hearing loss had not yet been identified in the younger UNHS children in our study. Our findings of late identification in 26.7% of 75 screened children are consistent with conclusions that a substantial number of children develop hearing loss after the newborn period (Johnson et al. 2005; White & Muñoz 2008; Lü et al. 2011; Watkin & Baldwin 2011).
One reason advanced for targeting MBUHL is to adequately follow-up children for progression of hearing loss. Our finding that 22% of all children and 32.4% of children since UNHS implementation experienced deterioration in hearing supports this rationale (Hyde 2005). It is noteworthy that almost one third of children with UHL experienced more than 20 dB deterioration or progression to bilateral loss, a finding consistent with other studies of children diagnosed after failing screening in one ear (Neault 2005; Declau et al. 2008). Given that 50% of the pre-UNHS children were not identified with hearing loss until after the age of 5 years, these numbers likely underestimate progressive hearing loss.
Etiology was known in less than half of the children, a finding consistent with other reports (Russ et al. 2003; Declau et al. 2008). In our study, 26.7% of children had been admitted to the NICU, a well-established risk factor for hearing loss (Joint Committee on Infant Hearing 2007), which has resulted in separate protocol recommendations for NICU nurseries (Hyde 2005). Only 5 children presented with enlarged vestibular aqueduct syndrome and 1 with congenital CMV although these have been reported as important causes for late-onset hearing loss (Nance et al. 2006). However, this finding likely reflects the absence of medical workup targeting these particular conditions.
Our study showed a dramatic decrease in the age of confirmation of MBUHL after implementation of UNHS, from a median age of 5.0 to 0.8 years. Specifically for children with UHL, the median age was lowered from 5.3 to 0.3 years. In 2007, the Joint Committee on Infant Hearing stated the importance of identifying all childhood hearing disorders, while recognizing that current technologies may miss some mild hearing loss (Cone-Wesson et al. 2000; Johnson et al. 2005). Our research shows that UNHS can contribute to the early identification of many children with MBUHL. Similarly, Holte et al. (2012) reported that in children who underwent newborn hearing screening, severity of hearing loss was not associated with age at confirmation or intervention. These results appear to contrast with the concerns of some investigators that infants with milder hearing loss are not being identified through UNHS programs (White & Muñoz 2008; Porter & Bess 2011).
In countries where UNHS is standard care, children with MBUHL are likely to be identified at much younger ages than previously. A challenging aspect of providing optimal care is the relative uncertainty related to amplification. While there is good consensus on the benefits of amplification for children with more severe hearing loss (Bagatto et al. 2010; King 2010), protocols are less well-established for children with MBUHL (Tharpe 2008; McKay et al. 2008). It is interesting to note that, 87.2% of children eventually received amplification recommendations, suggesting that audiologists judged amplification to be beneficial for most. Time from hearing-loss identification to amplification ranged from immediate to more than 6-year delays, suggesting uncertainty about management options. For the 275 children with bilateral hearing loss, our analysis revealed that later age at identification was significantly associated with audiologists’ decisions concerning amplification. One explanation is that clinicians made decisions based on information from parents and schools about older children’s functioning. These findings suggest that audiologists may feel more comfortable with the accuracy of information and with access to a wider range of technology options (e.g., open-fit hearing aids) for slightly older children. For children with bilateral losses, severity in the better ear also influenced amplification-related decisions. For children with UHL, there was no clear association between amplification decisions and age at confirmation or degree of hearing loss in the impaired ear. However, this finding should be interpreted with caution in view of the much smaller number of children in the UHL group and particularly the small number who received amplification at confirmation.
In contrast to earlier studies that reported less than 50% amplification use in children with MBUHL (Davis et al. 2002; Reeve 2005), our results indicated that 70.2% regularly used amplification, possibly reflecting earlier age at amplification in recent years. To date, there is little information to support whether amplification or other interventions including family support are likely to reduce or prevent the effects of MBUHL. Careful monitoring of outcomes both in terms of amplification use and impact on development is required to document the benefits of early identification.
A major strength of this study is the access to population-based prospective data for one entire region over a 20-year period, which permitted comparisons before and after UNHS initiatives. However, while we demonstrated that many more children with MBUHL were being identified and managed at younger ages than previously, without follow-up of children who passed the screen, we are unable to determine the true effectiveness of screening. It is therefore possible that some children identified as having late-onset hearing loss had minimal degrees of loss at screening, which went undetected until parental concerns arose at a later age. Additional important weaknesses are the reliance on chart data to determine amplification use and the lack of outcome data that could contribute to a better understanding of the variation in clinical practices. In some cases, audiologists’ amplification decisions may have been impacted by parental reluctance but this information was not systematically available for analysis. Given the apparent degree of indecision concerning amplification for these children, it is also important to underscore that provider uncertainty may have affected parents’ understanding of the potential benefits of amplification as well as their commitment to using hearing devices after fitting. Our findings point to the need for further research about the advantages of amplification in the early years and for continuing education for clinicians on how to manage this population. Furthermore, in this study, information related to socioeconomic status was not available. Although hearing aids are partially subsidized in the public health care system, for some children, socioeconomic status may have impacted parental decision making related to amplification. Finally, parents’ participation in therapy may have influenced their decisions about proceeding with recommendations for and subsequent use of amplification. In this publicly funded program, children with all degrees of hearing had access to early intervention services as standard practice. Although enrolment in speech-language intervention was documented in the medical charts and specific details such as amount of therapy might have contributed additional information, these details were not extracted for this particular study.
This study confirms that one outcome of UNHS is a clinical population of young children with MBUHL who require services. Although, not a new population, they represent a group of children who are different from those previously identified with MBUHL because of their earlier age at confirmation of hearing loss. Given the limited evidence base to guide treatment decisions, continued collection of information about clinical care has important implications for the management of this new clientele. Our work suggests that UNHS increases the likelihood that infants with hearing loss will receive amplification at a young age, and that clinical practice is leaning toward fitting amplification as a standard of care well before school entry. One clinical consequence is that these children will continue to require follow-up and draw on clinical resources much earlier than previous generations. There is limited information on the effects of MBUHL when identified during infancy and the early preschool years. It remains to be seen whether achieving early identification and early amplification will positively affect outcomes for these children.
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