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Variations in the Prevalence of Hearing Loss in Children: Truth or Artifact?

Epidemiologic estimates of the prevalence of childhood hearing loss (HL) are important to public health and policy for a host of reasons. On the public health front, estimating the disease and disability burden of HL influences priorities in health care and research, determines whether preventionstrategiesareeffective, and tracks longitudinal progressionvsnewonsetofHL in the population. On a policy level, knowing the prevalence of HL in children helps policymakers allocate resources needed in the schools to rehabilitate and accommodate children and adolescents with HL, as mandated by the Individuals with Disability Education Act part C, and contributes to understanding the overall societal cost as children with HL grow into adulthood. However,epidemiologicalstudieshavereportedlargedifferences in the prevalence of childhood HL over time, from approximately 1 in 1000 to 19.5%.1,2 Why do the estimates of prevalence of childhood HL vary so widely in the literature? First, disparate definitions of what constitutes HL prevent easy summary or synthesis of the numbers. In the past, only bilateral HL of more than 40 decibel (dB) pure-tone averages (PTA) (ie, moderate or worse HL) were counted.1 In more recent studies,3,4 the thresholds for defining HL have decreased to mild HL (>25 dB) or slight HL (>15 dB), investigators have evaluated low-frequency or high-frequency PTAs, as well as unilateral and bilateral HL. All of these recent changes in definition of HL increase the prevalence. Second, how the hearing data are acquired affects the prevalence estimates. Whether the hearing thresholds are obtained in sound-treated rooms or in quiet rooms; estimates are obtained via self-report or ascertained with audiometers; tympanograms or otoacoustic emissions are acquired to attempt to separate conductive from sensorineural HL; and whether bone and air conduction thresholds are measured; all of these factors affect the quality of primary data. Third, because epidemiologic studies cannot test every child in a target population, they are subject to several biases. These biases include sampling bias, when cross-sectional studies choose one child and assume that other children of similar demographic and socioeconomic background are represented by that child; selection bias, when factors associated with a parent allowing the child to participate in a study but not measured by the investigators skew the results; and biases related to follow-up in cohort studies, when factors that result in a child not participating in subsequent evaluations are not distributed equally among those with and without hearing loss. Finally, the age range of the sample population matters, because the prevalence of HL increases as children grow older, owing to delayed onset of congenital and/or hereditary HL and acquired HL. Two new studies3,4 estimate the prevalence of childhood HL using different study designs and age groups but arrive at similar conclusions. le Clerq and colleagues report an overall 17.5% prevalence of HL among children ages 9 to 11 years in the Generation R study,3 a longitudinal study based in Rotterdam, the Netherlands. Based on tympanogram data combined with hearing thresholds, the investigators estimated 7.8% had a sensorineural HL while 6.3% had conductive HL, and 3.5% had HL of unknown origin. Su and Chan4 report an overall 15.2% prevalence of HL among US adolescents ages 12 to 19 years in the National Health and Nutrition Examination Survey (NHANES) 2009-2010, a cross-sectional study.4 They reported this as a decrease from the 22.5% peak prevalence seen in the NHANES 2007-2008 survey. Both studies used hearing thresholds more than 15 dB in at least 1 ear as their definition of HL and used only air conduction thresholds. Both studies have significant potential for bias from nonparticipation or exclusion of data; 37% of the eligible population of the Generation R study did not participate, and data from 18% of the NHANES populations were excluded due to incomplete examinations or discrepancy in testing thresholds. Both studies show an association of HL with a history of recurrent otitis media and lower socioeconomic status, measured by maternal education status in the Generation R study3 and poverty income ratio in the NHANES study. How do these 2 studies compare in their estimates with other epidemiological studies of HL in children and adolescents? The Table summarizes large studies published since 2010 from across the globe. The main difficulty in trying to compare the prevalence is that the hearing thresholds used to define HL are so different. Feder et al5 from Canada comes the closest to these 2 studies, reporting 7.7% of children and adolescents ages 6 to 19 years had any HL as defined as any PTA more than 20 dB. As soon as the threshold for defining HL increases, the prevalence of HL decreases. If the reduction in the prevalence of HL from the NHANES 2009-2010 data is true, we may speculate about some of the mitigating factors that may have influenced the estimates. These mitigating factors are suggested in the risk factors for HL, namely recurrent otitis media and low socioeconomic status, which were noted by both Su and Chan4 and le Clerq et al3 in their analyses. The children in the latest NHANES sample4 may have been more likely to have received the pneumococcal conjugate vaccines that became available in 2000 (https://www.cdc.gov/vaccines/pubs/pinkbook/pneumo .html) and have significantly decreased the burden of otitis media. In addition, the Children’s Health Insurance Program, created in 1997, would have provided more access to health care, including preventative health care and immunizations that may have influenced the decrease in HL. Related articles Variations in the Prevalence of Hearing Loss in Children Invited Commentary