Kurt A. Stone, MD

In 1993 a consensus statement from the National Institutes of Health (NIH)¹ recommended universal newborn hearing screening by the age of 3 months and also stated that otoacoustic emission might be the technology used for screening. These recommendations were based on the following: (1) the incidence of hearing loss is 1 to 6 per 1000; (2) only one half of the infants with hearing loss are discovered with high-risk screening; (3) the current average age at diagnosis of hearing loss is 2.5 years; and (4) early identification and treatment by the age of 6 months will improve outcomes.¹ The 1994 position statement from the Joint Committee on Infant Hearing² reiterated this recommendation.

Bess and Paradise³ and Paradise⁴ succinctly enumerated the difficulties with universal screening, including high false-positive rates, overall expense, patient acceptance, and feasibility. Since 1993, research and publications^5-9 have supported universal screening; now the cost of identifying an infant with hearing loss is less than the cost of identifying an infant with phenylketonuria.¹⁰ Also, studies by Appuzzo and Yoshinaga-Itano¹¹ and Yoshinaga-Itano and colleagues¹² showed early identification and intervention improves language and social development, and today 37 states have more than 1 hospital providing universal hearing screening programs.¹³ A variety of screening devices are used, including automated auditory brainstem responses (AABR), transient evoked otoacoustic emission, and distortion product otoacoustic emissions (DPOAE).

Methods

Study Group

Well infants hospitalized from 24 to 72 hours were screened at ages 6 to 72 hours. Data was obtained from a sample of 1002 infants screened at Rapid City Regional Hospital between February 1997 and March 1999. During that period, newborn infants receiving care from family physicians and a pediatrician in the regular nursery were screened. Specific statistics on the age of each infant at screening were not kept.

The screening team consisted of a family practice physician, a registered nurse, and 2 family practice residents. All members of the team performed hearing screening.

We explained the hearing screen procedure, methods, risks, and benefits to the parents of the patient, and obtained informed consent. The follow-up plan for failed hearing screens was also outlined.

Equipment

The GSI 60 computer-based DPOAE instrument (Grason-Stadler, Inc, Milford, NH) was used to perform screenings. It generates paired frequencies F1 (65 dB) and F2 (55 dB). These frequencies travel through the middle ear to the cochlea, where a third tone is generated at the outer hair cell level. Normal cochlear stimulation in this manner produces a DPOAE at a specific frequency predicted by the formula 2F1-F2. During distortion product measurement, the frequency range of 2000 to 4000 Hz was selected for distortion product frequencies.

Procedure

The initial DPOAE measure was obtained on the morning of hospital discharge, with most infants tested between the ages of 12 and 72 hours. Average actual DPOAE screen time was 20 minutes. Passing the test was defined as an emission signal reproducible at 3 frequencies on 2 separate tests. The distortion product was required to be 5 decibels above the noise floor to be considered a pass.

Infants who failed the DPOAE measure were rescreened using DPOAE at 8 weeks. All second-stage screen failures were screened with tympanometry and DPOAE and were referred to their private physician or an ear, nose, and throat specialist. Infants that failed DPOAE and passed tympanometry were to be referred for diagnostic auditory brain response testing (Figure).

Results

Of the 1002 infants screened, 11.1% (111) failed the initial screening (Table 1). Seventy-nine infants were returned to our clinic for retesting 1 to 3 months after their initial evaluation. Two infants (0.2% of the total) failed the second screening. One infant failed the second screen and the tympanogram. He was treated and he passed the third DPOAE. An additional infant failed the repeat screen but passed the tympanogram. She was referred for auditory brain response testing and was found to have mild sensory neural hearing loss. A total of 32 infants were lost to follow-up despite frequent attempts to contact parents by telephone and mail.

Discussion

Recent advances in technology have provided the means to screen newborns and infants for hearing deficits. The 2 most commonly used technologies are AABRs and otoacoustic emissions. Otoacoustic emissions were first described by Kemp in 1978. The cochlear basal membrane vibrates when stimulated by sound, and this vibration sends a retrograde wave back through the cochlear fluid that ultimately vibrates the eardrum, producing a sound wave that can be detected by a microphone at the external ear. DPOAE are produced by stimulating the cochlea with a series of 2 specific frequencies, resulting in a single predictable frequency response.¹⁴ Transient evoked otoacoustic emissions, an alternative to DPOAE, are evoked by a click that results in the emission of several frequencies at the same time. AABRs are also used in screening programs, with the advantage of testing both the cochlea and retrocochlear functions. However, the majority of infants with hearing loss have cochlear deficits.¹⁵ Otoacoustic emission testing can be done with the infant awake, feeding, or sucking on a pacifier. AABR requires the infant to be asleep. Currently, it is unknown which screening test or combination of tests is best. A few studies have compared various screening methods, but no consensus has been reached.^16,17 Twenty-two states currently mandate some form of newborn universal hearing screening.¹⁸

We looked at the feasibility of universal infant hearing screening and whether it meets the criteria for screening tests discussed by Frame and coworkers.¹⁹

Disease Recognition

Is there an identifiable disease? Yes. The NIH consensus statement1 identified the risk of hearing loss at 1 per 1000 births. Other studies have found a base rate of from 2 per 1000 to as high as 5 to 9.75 per 1000 in high-risk infants.^5-8,20 Without universal screening, the average age at which a deaf child is identified is 2.5 years.¹ Typically, these children are tested because of a delay in language and speech skills. The goal of any screening program is to identify and effectively treat a disease in the asymptomatic stage.¹⁹ Unfortunately, not all infant hearing loss is identifiable at birth. Approximately 20% to 30% of children develop their deafness in the first few months of life.¹ Because of this, health care systems must be vigilant and have a low threshold for repeat screening in older infants. Assuming a hearing loss incidence of 1 per 1000, a birthrate of 4 million per year, and the ability to detect 80% of affected newborns, 3200 infants per year could be diagnosed with hearing loss.

Early Identification

Does early identification and intervention while the infant is asymptomatic improve outcomes? The experts who developed the NIH consensus statement¹ stated that early intervention probably does improve outcomes. When this statement was made, however, there had not been adequate studies showing improved outcomes with intervention by the age of 6 months. Since then there have been 2 studies showing significant improvement in expressive and receptive language skills in infants diagnosed and treated before the age of 6 months. Apuzzo and Yoshinaga-Itano¹¹ showed significant improvement in language skills in study of a subset of infants diagnosed before the age of 2 months. Their study included 63 infants, and only those with severe hearing loss (23 infants) had a statistically significant improvement in outcomes. Infants with profound, mild, and mild-to-moderate hearing loss did not have significant improvement. A later study by Yoshinaga and colleagues¹² revealed significant improvement in all categories of hearing loss when diagnosed and treated before the age of 6 months. Of the 150 infants in that study, 72 were diagnosed before the age of 6 months, and 78 were diagnosed after the age of 6 months. The early-identified infants had significantly better language skills regardless of the degree of hearing loss, socioeconomic class, and level of cognitive skills. Early diagnosis needs to be coupled with an effective intervention program.¹ The intervention should be multidisciplinary and include a physician experienced in otologic disorders, an audiologist with experience in infants and hearing augmentation, a speech and language pathologist, a sign language specialist, and family support services.²

Sensitivity and Specificity

What are the false-negative and false-positive rates of the test? In Rhode Island, universal screening began in 1991 using otoacoustic emission testing. In an article by Vohr and coworkers⁹ only 5 infants with sensorineural hearing loss had passed the initial screen (false-negatives). Of the 47,257 infants screened there were 106 true-positives, so the sensitivity was 95%. Mehl and Thompson8 reported on the Colorado screening program that used either otoacoustic emissions or AABR. There were no false-negatives, and 41,796 infants were screened. At the other end of the spectrum, Lutman and coworkers²¹ found a false-negative rate of 20% in high-risk infants screened with otoacoustic testing. The majority of these infants were from the newborn intensive care unit and thus were at higher risk for central nervous system disease (eg, kernicterus, cytomegalovirus) and associated hearing loss. Otoacoustic emissions are normal in infants with hearing loss secondary to central lesions. This may account for some of the false-negative tests in that study.^15,22 Infants with known central nervous system disease should probably be evaluated with auditory brain response testing. There has not been a controlled long-term study specifically evaluating the actual false-negative rate in a universal screening program. In the Rhode Island and Colorado groups the false-negative rate appears to be very low. Our study was not designed to determine a false-negative rate. The large number of required subjects (50,000)²¹ and the length of time required to do a meaningful assessment of the false-negative rate were beyond the scope of our study.

There is a consistently high false-positive rate for infants tested in the newborn nursery—between 3.5% and 10%.^5-9,20 This is in part because of matter (vernix) in the newborn ear, the background noise in the nursery, and fluid in the middle ear. The fluid and vernix clear spontaneously during the first few days of life. As a result, most studies repeat the failed newborn screens at the age of 2 to 8 weeks. Infants who fail the second screen are referred for diagnostic auditory brain response testing. The overall failure rate after the second screen was 1% or even less in the referenced studies.^59,20 The actual rate of sensorineural hearing loss in these studies is 1 to 2 per 1000. Thus, for every 1000 infants tested, approximately 10 were referred for diagnostic auditory brain testing. The rate of true sensorineural hearing loss was 1 to 2 per 1000. Therefore, 5 to 10 diagnostic auditory brain response tests were done to find each infant with hearing loss. The positive predictive value (PPV) for infants who failed the second screen was 16% in the Rhode Island study and between 5% and 19% in Colorado.^8,9 In comparison, the PPV for hypothyroidism screening is 3% and is 80% for phenylketonuria screening.⁸

Cost-Effectiveness

It appears universal screening will be cost effective, but no studies have been done to prove this. In our study the cost was just higher than $22,000 dollars to find 1 low-risk infant with hearing loss (Tables 2 and 3). Costs in other studies have ranged from $4000 to $17,500 per child identified with hearing loss.^6-8 The significant factor when comparing these costs is the actual incidence of hearing loss. Studies with lower costs per identified child had a higher incidence of hearing loss. For example, if our study had found 2 children with sensorineural hearing loss, the cost per child diagnosed would have been just higher than $11,000. This cost of hearing screens can then be compared with the cost of identifying infants with phenylketonuria disease (~$10,000) and hypothyroidism (~$40,000) per child given the diagnosis.^8,10 There is a clear cost benefit with phenylketonuria and hyperthyroid screening, but a cost benefit has not been proved with universal hearing screening. The potential for cost savings relies on fewer children requiring special education and fewer adults on long-term disability. The state of South Dakota provides an in-residence school for the deaf at no cost for state residents but charges approximately $15,000 per year for patients who are residents of other states. In-residence schooling in other states can cost as much as $30,000 per year.¹⁰ This is approximately 4 times the cost of regular schooling. If only a portion of the early-identified infants attended 12 years of regular school, universal screening would be cost-beneficial. A study comparing schooling costs in early-identified infants versus late-identified infants has not been done.

Is it feasible for rural states to implement a universal hearing screening program? Our study found infants could be successfully screened at a specified time rather than waiting for the infant to be perfectly quiet. Therefore, otoacoustic emission testing lends itself to being taken on the road, and the same equipment and personnel can be used to test infants at a number of hospitals within a 100-mile radius. The software is user friendly, and the cost of otoacoustic emission devices has dropped to approximately $7000. Wyoming began implementation of a universal hearing screening program in 1994, and as of 1998 that program has been fully implemented. In 1998, 95% of all infants born in Wyoming were successfully screened.²³ Universal hearing screening can be done, and has been done in rural states and communities.

Conclusions

Testing only high-risk newborn infants results, at best, in early identification of only half of the infants with hearing loss.¹ Universal screening is the only effective way to identify the majority of newborn infants with hearing loss. Early identification and treatment has been shown to significantly improve expressive and receptive language skills in infants and children with hearing loss. For this reason, it is clearly worthwhile to pursue universal screening. However, long-term patient outcomes and cost benefits should be studied.

Acknowledgments

We would like to thank the Children’s Miracle Network at Rapid City Regional Hospital, which provided funding of $13,562.50 to purchase the otoacoustic testing equipment.

We also thank Douglas A. Bright, MD, program director, Rapid City Regional Hospital Family Practice Residency, for his guidance and support with our project.

In 1993 a consensus statement from the National Institutes of Health (NIH)¹ recommended universal newborn hearing screening by the age of 3 months and also stated that otoacoustic emission might be the technology used for screening. These recommendations were based on the following: (1) the incidence of hearing loss is 1 to 6 per 1000; (2) only one half of the infants with hearing loss are discovered with high-risk screening; (3) the current average age at diagnosis of hearing loss is 2.5 years; and (4) early identification and treatment by the age of 6 months will improve outcomes.¹ The 1994 position statement from the Joint Committee on Infant Hearing² reiterated this recommendation.

Bess and Paradise³ and Paradise⁴ succinctly enumerated the difficulties with universal screening, including high false-positive rates, overall expense, patient acceptance, and feasibility. Since 1993, research and publications^5-9 have supported universal screening; now the cost of identifying an infant with hearing loss is less than the cost of identifying an infant with phenylketonuria.¹⁰ Also, studies by Appuzzo and Yoshinaga-Itano¹¹ and Yoshinaga-Itano and colleagues¹² showed early identification and intervention improves language and social development, and today 37 states have more than 1 hospital providing universal hearing screening programs.¹³ A variety of screening devices are used, including automated auditory brainstem responses (AABR), transient evoked otoacoustic emission, and distortion product otoacoustic emissions (DPOAE).

Methods

Study Group

Well infants hospitalized from 24 to 72 hours were screened at ages 6 to 72 hours. Data was obtained from a sample of 1002 infants screened at Rapid City Regional Hospital between February 1997 and March 1999. During that period, newborn infants receiving care from family physicians and a pediatrician in the regular nursery were screened. Specific statistics on the age of each infant at screening were not kept.

The screening team consisted of a family practice physician, a registered nurse, and 2 family practice residents. All members of the team performed hearing screening.

We explained the hearing screen procedure, methods, risks, and benefits to the parents of the patient, and obtained informed consent. The follow-up plan for failed hearing screens was also outlined.

Equipment

The GSI 60 computer-based DPOAE instrument (Grason-Stadler, Inc, Milford, NH) was used to perform screenings. It generates paired frequencies F1 (65 dB) and F2 (55 dB). These frequencies travel through the middle ear to the cochlea, where a third tone is generated at the outer hair cell level. Normal cochlear stimulation in this manner produces a DPOAE at a specific frequency predicted by the formula 2F1-F2. During distortion product measurement, the frequency range of 2000 to 4000 Hz was selected for distortion product frequencies.

Procedure

The initial DPOAE measure was obtained on the morning of hospital discharge, with most infants tested between the ages of 12 and 72 hours. Average actual DPOAE screen time was 20 minutes. Passing the test was defined as an emission signal reproducible at 3 frequencies on 2 separate tests. The distortion product was required to be 5 decibels above the noise floor to be considered a pass.

Infants who failed the DPOAE measure were rescreened using DPOAE at 8 weeks. All second-stage screen failures were screened with tympanometry and DPOAE and were referred to their private physician or an ear, nose, and throat specialist. Infants that failed DPOAE and passed tympanometry were to be referred for diagnostic auditory brain response testing (Figure).

Results

Of the 1002 infants screened, 11.1% (111) failed the initial screening (Table 1). Seventy-nine infants were returned to our clinic for retesting 1 to 3 months after their initial evaluation. Two infants (0.2% of the total) failed the second screening. One infant failed the second screen and the tympanogram. He was treated and he passed the third DPOAE. An additional infant failed the repeat screen but passed the tympanogram. She was referred for auditory brain response testing and was found to have mild sensory neural hearing loss. A total of 32 infants were lost to follow-up despite frequent attempts to contact parents by telephone and mail.

Discussion

Recent advances in technology have provided the means to screen newborns and infants for hearing deficits. The 2 most commonly used technologies are AABRs and otoacoustic emissions. Otoacoustic emissions were first described by Kemp in 1978. The cochlear basal membrane vibrates when stimulated by sound, and this vibration sends a retrograde wave back through the cochlear fluid that ultimately vibrates the eardrum, producing a sound wave that can be detected by a microphone at the external ear. DPOAE are produced by stimulating the cochlea with a series of 2 specific frequencies, resulting in a single predictable frequency response.¹⁴ Transient evoked otoacoustic emissions, an alternative to DPOAE, are evoked by a click that results in the emission of several frequencies at the same time. AABRs are also used in screening programs, with the advantage of testing both the cochlea and retrocochlear functions. However, the majority of infants with hearing loss have cochlear deficits.¹⁵ Otoacoustic emission testing can be done with the infant awake, feeding, or sucking on a pacifier. AABR requires the infant to be asleep. Currently, it is unknown which screening test or combination of tests is best. A few studies have compared various screening methods, but no consensus has been reached.^16,17 Twenty-two states currently mandate some form of newborn universal hearing screening.¹⁸

We looked at the feasibility of universal infant hearing screening and whether it meets the criteria for screening tests discussed by Frame and coworkers.¹⁹

Disease Recognition

Is there an identifiable disease? Yes. The NIH consensus statement1 identified the risk of hearing loss at 1 per 1000 births. Other studies have found a base rate of from 2 per 1000 to as high as 5 to 9.75 per 1000 in high-risk infants.^5-8,20 Without universal screening, the average age at which a deaf child is identified is 2.5 years.¹ Typically, these children are tested because of a delay in language and speech skills. The goal of any screening program is to identify and effectively treat a disease in the asymptomatic stage.¹⁹ Unfortunately, not all infant hearing loss is identifiable at birth. Approximately 20% to 30% of children develop their deafness in the first few months of life.¹ Because of this, health care systems must be vigilant and have a low threshold for repeat screening in older infants. Assuming a hearing loss incidence of 1 per 1000, a birthrate of 4 million per year, and the ability to detect 80% of affected newborns, 3200 infants per year could be diagnosed with hearing loss.

Early Identification

Does early identification and intervention while the infant is asymptomatic improve outcomes? The experts who developed the NIH consensus statement¹ stated that early intervention probably does improve outcomes. When this statement was made, however, there had not been adequate studies showing improved outcomes with intervention by the age of 6 months. Since then there have been 2 studies showing significant improvement in expressive and receptive language skills in infants diagnosed and treated before the age of 6 months. Apuzzo and Yoshinaga-Itano¹¹ showed significant improvement in language skills in study of a subset of infants diagnosed before the age of 2 months. Their study included 63 infants, and only those with severe hearing loss (23 infants) had a statistically significant improvement in outcomes. Infants with profound, mild, and mild-to-moderate hearing loss did not have significant improvement. A later study by Yoshinaga and colleagues¹² revealed significant improvement in all categories of hearing loss when diagnosed and treated before the age of 6 months. Of the 150 infants in that study, 72 were diagnosed before the age of 6 months, and 78 were diagnosed after the age of 6 months. The early-identified infants had significantly better language skills regardless of the degree of hearing loss, socioeconomic class, and level of cognitive skills. Early diagnosis needs to be coupled with an effective intervention program.¹ The intervention should be multidisciplinary and include a physician experienced in otologic disorders, an audiologist with experience in infants and hearing augmentation, a speech and language pathologist, a sign language specialist, and family support services.²

Sensitivity and Specificity

What are the false-negative and false-positive rates of the test? In Rhode Island, universal screening began in 1991 using otoacoustic emission testing. In an article by Vohr and coworkers⁹ only 5 infants with sensorineural hearing loss had passed the initial screen (false-negatives). Of the 47,257 infants screened there were 106 true-positives, so the sensitivity was 95%. Mehl and Thompson8 reported on the Colorado screening program that used either otoacoustic emissions or AABR. There were no false-negatives, and 41,796 infants were screened. At the other end of the spectrum, Lutman and coworkers²¹ found a false-negative rate of 20% in high-risk infants screened with otoacoustic testing. The majority of these infants were from the newborn intensive care unit and thus were at higher risk for central nervous system disease (eg, kernicterus, cytomegalovirus) and associated hearing loss. Otoacoustic emissions are normal in infants with hearing loss secondary to central lesions. This may account for some of the false-negative tests in that study.^15,22 Infants with known central nervous system disease should probably be evaluated with auditory brain response testing. There has not been a controlled long-term study specifically evaluating the actual false-negative rate in a universal screening program. In the Rhode Island and Colorado groups the false-negative rate appears to be very low. Our study was not designed to determine a false-negative rate. The large number of required subjects (50,000)²¹ and the length of time required to do a meaningful assessment of the false-negative rate were beyond the scope of our study.

There is a consistently high false-positive rate for infants tested in the newborn nursery—between 3.5% and 10%.^5-9,20 This is in part because of matter (vernix) in the newborn ear, the background noise in the nursery, and fluid in the middle ear. The fluid and vernix clear spontaneously during the first few days of life. As a result, most studies repeat the failed newborn screens at the age of 2 to 8 weeks. Infants who fail the second screen are referred for diagnostic auditory brain response testing. The overall failure rate after the second screen was 1% or even less in the referenced studies.^59,20 The actual rate of sensorineural hearing loss in these studies is 1 to 2 per 1000. Thus, for every 1000 infants tested, approximately 10 were referred for diagnostic auditory brain testing. The rate of true sensorineural hearing loss was 1 to 2 per 1000. Therefore, 5 to 10 diagnostic auditory brain response tests were done to find each infant with hearing loss. The positive predictive value (PPV) for infants who failed the second screen was 16% in the Rhode Island study and between 5% and 19% in Colorado.^8,9 In comparison, the PPV for hypothyroidism screening is 3% and is 80% for phenylketonuria screening.⁸

Cost-Effectiveness

It appears universal screening will be cost effective, but no studies have been done to prove this. In our study the cost was just higher than $22,000 dollars to find 1 low-risk infant with hearing loss (Tables 2 and 3). Costs in other studies have ranged from $4000 to $17,500 per child identified with hearing loss.^6-8 The significant factor when comparing these costs is the actual incidence of hearing loss. Studies with lower costs per identified child had a higher incidence of hearing loss. For example, if our study had found 2 children with sensorineural hearing loss, the cost per child diagnosed would have been just higher than $11,000. This cost of hearing screens can then be compared with the cost of identifying infants with phenylketonuria disease (~$10,000) and hypothyroidism (~$40,000) per child given the diagnosis.^8,10 There is a clear cost benefit with phenylketonuria and hyperthyroid screening, but a cost benefit has not been proved with universal hearing screening. The potential for cost savings relies on fewer children requiring special education and fewer adults on long-term disability. The state of South Dakota provides an in-residence school for the deaf at no cost for state residents but charges approximately $15,000 per year for patients who are residents of other states. In-residence schooling in other states can cost as much as $30,000 per year.¹⁰ This is approximately 4 times the cost of regular schooling. If only a portion of the early-identified infants attended 12 years of regular school, universal screening would be cost-beneficial. A study comparing schooling costs in early-identified infants versus late-identified infants has not been done.

Is it feasible for rural states to implement a universal hearing screening program? Our study found infants could be successfully screened at a specified time rather than waiting for the infant to be perfectly quiet. Therefore, otoacoustic emission testing lends itself to being taken on the road, and the same equipment and personnel can be used to test infants at a number of hospitals within a 100-mile radius. The software is user friendly, and the cost of otoacoustic emission devices has dropped to approximately $7000. Wyoming began implementation of a universal hearing screening program in 1994, and as of 1998 that program has been fully implemented. In 1998, 95% of all infants born in Wyoming were successfully screened.²³ Universal hearing screening can be done, and has been done in rural states and communities.

Conclusions

Testing only high-risk newborn infants results, at best, in early identification of only half of the infants with hearing loss.¹ Universal screening is the only effective way to identify the majority of newborn infants with hearing loss. Early identification and treatment has been shown to significantly improve expressive and receptive language skills in infants and children with hearing loss. For this reason, it is clearly worthwhile to pursue universal screening. However, long-term patient outcomes and cost benefits should be studied.

Acknowledgments

We would like to thank the Children’s Miracle Network at Rapid City Regional Hospital, which provided funding of $13,562.50 to purchase the otoacoustic testing equipment.

We also thank Douglas A. Bright, MD, program director, Rapid City Regional Hospital Family Practice Residency, for his guidance and support with our project.

In 1993 a consensus statement from the National Institutes of Health (NIH)¹ recommended universal newborn hearing screening by the age of 3 months and also stated that otoacoustic emission might be the technology used for screening. These recommendations were based on the following: (1) the incidence of hearing loss is 1 to 6 per 1000; (2) only one half of the infants with hearing loss are discovered with high-risk screening; (3) the current average age at diagnosis of hearing loss is 2.5 years; and (4) early identification and treatment by the age of 6 months will improve outcomes.¹ The 1994 position statement from the Joint Committee on Infant Hearing² reiterated this recommendation.

Bess and Paradise³ and Paradise⁴ succinctly enumerated the difficulties with universal screening, including high false-positive rates, overall expense, patient acceptance, and feasibility. Since 1993, research and publications^5-9 have supported universal screening; now the cost of identifying an infant with hearing loss is less than the cost of identifying an infant with phenylketonuria.¹⁰ Also, studies by Appuzzo and Yoshinaga-Itano¹¹ and Yoshinaga-Itano and colleagues¹² showed early identification and intervention improves language and social development, and today 37 states have more than 1 hospital providing universal hearing screening programs.¹³ A variety of screening devices are used, including automated auditory brainstem responses (AABR), transient evoked otoacoustic emission, and distortion product otoacoustic emissions (DPOAE).

Methods

Study Group

Well infants hospitalized from 24 to 72 hours were screened at ages 6 to 72 hours. Data was obtained from a sample of 1002 infants screened at Rapid City Regional Hospital between February 1997 and March 1999. During that period, newborn infants receiving care from family physicians and a pediatrician in the regular nursery were screened. Specific statistics on the age of each infant at screening were not kept.

The screening team consisted of a family practice physician, a registered nurse, and 2 family practice residents. All members of the team performed hearing screening.

We explained the hearing screen procedure, methods, risks, and benefits to the parents of the patient, and obtained informed consent. The follow-up plan for failed hearing screens was also outlined.

Equipment

The GSI 60 computer-based DPOAE instrument (Grason-Stadler, Inc, Milford, NH) was used to perform screenings. It generates paired frequencies F1 (65 dB) and F2 (55 dB). These frequencies travel through the middle ear to the cochlea, where a third tone is generated at the outer hair cell level. Normal cochlear stimulation in this manner produces a DPOAE at a specific frequency predicted by the formula 2F1-F2. During distortion product measurement, the frequency range of 2000 to 4000 Hz was selected for distortion product frequencies.

Procedure

The initial DPOAE measure was obtained on the morning of hospital discharge, with most infants tested between the ages of 12 and 72 hours. Average actual DPOAE screen time was 20 minutes. Passing the test was defined as an emission signal reproducible at 3 frequencies on 2 separate tests. The distortion product was required to be 5 decibels above the noise floor to be considered a pass.

Infants who failed the DPOAE measure were rescreened using DPOAE at 8 weeks. All second-stage screen failures were screened with tympanometry and DPOAE and were referred to their private physician or an ear, nose, and throat specialist. Infants that failed DPOAE and passed tympanometry were to be referred for diagnostic auditory brain response testing (Figure).

Results

Of the 1002 infants screened, 11.1% (111) failed the initial screening (Table 1). Seventy-nine infants were returned to our clinic for retesting 1 to 3 months after their initial evaluation. Two infants (0.2% of the total) failed the second screening. One infant failed the second screen and the tympanogram. He was treated and he passed the third DPOAE. An additional infant failed the repeat screen but passed the tympanogram. She was referred for auditory brain response testing and was found to have mild sensory neural hearing loss. A total of 32 infants were lost to follow-up despite frequent attempts to contact parents by telephone and mail.

Discussion

Recent advances in technology have provided the means to screen newborns and infants for hearing deficits. The 2 most commonly used technologies are AABRs and otoacoustic emissions. Otoacoustic emissions were first described by Kemp in 1978. The cochlear basal membrane vibrates when stimulated by sound, and this vibration sends a retrograde wave back through the cochlear fluid that ultimately vibrates the eardrum, producing a sound wave that can be detected by a microphone at the external ear. DPOAE are produced by stimulating the cochlea with a series of 2 specific frequencies, resulting in a single predictable frequency response.¹⁴ Transient evoked otoacoustic emissions, an alternative to DPOAE, are evoked by a click that results in the emission of several frequencies at the same time. AABRs are also used in screening programs, with the advantage of testing both the cochlea and retrocochlear functions. However, the majority of infants with hearing loss have cochlear deficits.¹⁵ Otoacoustic emission testing can be done with the infant awake, feeding, or sucking on a pacifier. AABR requires the infant to be asleep. Currently, it is unknown which screening test or combination of tests is best. A few studies have compared various screening methods, but no consensus has been reached.^16,17 Twenty-two states currently mandate some form of newborn universal hearing screening.¹⁸

We looked at the feasibility of universal infant hearing screening and whether it meets the criteria for screening tests discussed by Frame and coworkers.¹⁹

Disease Recognition

Is there an identifiable disease? Yes. The NIH consensus statement1 identified the risk of hearing loss at 1 per 1000 births. Other studies have found a base rate of from 2 per 1000 to as high as 5 to 9.75 per 1000 in high-risk infants.^5-8,20 Without universal screening, the average age at which a deaf child is identified is 2.5 years.¹ Typically, these children are tested because of a delay in language and speech skills. The goal of any screening program is to identify and effectively treat a disease in the asymptomatic stage.¹⁹ Unfortunately, not all infant hearing loss is identifiable at birth. Approximately 20% to 30% of children develop their deafness in the first few months of life.¹ Because of this, health care systems must be vigilant and have a low threshold for repeat screening in older infants. Assuming a hearing loss incidence of 1 per 1000, a birthrate of 4 million per year, and the ability to detect 80% of affected newborns, 3200 infants per year could be diagnosed with hearing loss.

Early Identification

Does early identification and intervention while the infant is asymptomatic improve outcomes? The experts who developed the NIH consensus statement¹ stated that early intervention probably does improve outcomes. When this statement was made, however, there had not been adequate studies showing improved outcomes with intervention by the age of 6 months. Since then there have been 2 studies showing significant improvement in expressive and receptive language skills in infants diagnosed and treated before the age of 6 months. Apuzzo and Yoshinaga-Itano¹¹ showed significant improvement in language skills in study of a subset of infants diagnosed before the age of 2 months. Their study included 63 infants, and only those with severe hearing loss (23 infants) had a statistically significant improvement in outcomes. Infants with profound, mild, and mild-to-moderate hearing loss did not have significant improvement. A later study by Yoshinaga and colleagues¹² revealed significant improvement in all categories of hearing loss when diagnosed and treated before the age of 6 months. Of the 150 infants in that study, 72 were diagnosed before the age of 6 months, and 78 were diagnosed after the age of 6 months. The early-identified infants had significantly better language skills regardless of the degree of hearing loss, socioeconomic class, and level of cognitive skills. Early diagnosis needs to be coupled with an effective intervention program.¹ The intervention should be multidisciplinary and include a physician experienced in otologic disorders, an audiologist with experience in infants and hearing augmentation, a speech and language pathologist, a sign language specialist, and family support services.²

Sensitivity and Specificity

What are the false-negative and false-positive rates of the test? In Rhode Island, universal screening began in 1991 using otoacoustic emission testing. In an article by Vohr and coworkers⁹ only 5 infants with sensorineural hearing loss had passed the initial screen (false-negatives). Of the 47,257 infants screened there were 106 true-positives, so the sensitivity was 95%. Mehl and Thompson8 reported on the Colorado screening program that used either otoacoustic emissions or AABR. There were no false-negatives, and 41,796 infants were screened. At the other end of the spectrum, Lutman and coworkers²¹ found a false-negative rate of 20% in high-risk infants screened with otoacoustic testing. The majority of these infants were from the newborn intensive care unit and thus were at higher risk for central nervous system disease (eg, kernicterus, cytomegalovirus) and associated hearing loss. Otoacoustic emissions are normal in infants with hearing loss secondary to central lesions. This may account for some of the false-negative tests in that study.^15,22 Infants with known central nervous system disease should probably be evaluated with auditory brain response testing. There has not been a controlled long-term study specifically evaluating the actual false-negative rate in a universal screening program. In the Rhode Island and Colorado groups the false-negative rate appears to be very low. Our study was not designed to determine a false-negative rate. The large number of required subjects (50,000)²¹ and the length of time required to do a meaningful assessment of the false-negative rate were beyond the scope of our study.

There is a consistently high false-positive rate for infants tested in the newborn nursery—between 3.5% and 10%.^5-9,20 This is in part because of matter (vernix) in the newborn ear, the background noise in the nursery, and fluid in the middle ear. The fluid and vernix clear spontaneously during the first few days of life. As a result, most studies repeat the failed newborn screens at the age of 2 to 8 weeks. Infants who fail the second screen are referred for diagnostic auditory brain response testing. The overall failure rate after the second screen was 1% or even less in the referenced studies.^59,20 The actual rate of sensorineural hearing loss in these studies is 1 to 2 per 1000. Thus, for every 1000 infants tested, approximately 10 were referred for diagnostic auditory brain testing. The rate of true sensorineural hearing loss was 1 to 2 per 1000. Therefore, 5 to 10 diagnostic auditory brain response tests were done to find each infant with hearing loss. The positive predictive value (PPV) for infants who failed the second screen was 16% in the Rhode Island study and between 5% and 19% in Colorado.^8,9 In comparison, the PPV for hypothyroidism screening is 3% and is 80% for phenylketonuria screening.⁸

Cost-Effectiveness

It appears universal screening will be cost effective, but no studies have been done to prove this. In our study the cost was just higher than $22,000 dollars to find 1 low-risk infant with hearing loss (Tables 2 and 3). Costs in other studies have ranged from $4000 to $17,500 per child identified with hearing loss.^6-8 The significant factor when comparing these costs is the actual incidence of hearing loss. Studies with lower costs per identified child had a higher incidence of hearing loss. For example, if our study had found 2 children with sensorineural hearing loss, the cost per child diagnosed would have been just higher than $11,000. This cost of hearing screens can then be compared with the cost of identifying infants with phenylketonuria disease (~$10,000) and hypothyroidism (~$40,000) per child given the diagnosis.^8,10 There is a clear cost benefit with phenylketonuria and hyperthyroid screening, but a cost benefit has not been proved with universal hearing screening. The potential for cost savings relies on fewer children requiring special education and fewer adults on long-term disability. The state of South Dakota provides an in-residence school for the deaf at no cost for state residents but charges approximately $15,000 per year for patients who are residents of other states. In-residence schooling in other states can cost as much as $30,000 per year.¹⁰ This is approximately 4 times the cost of regular schooling. If only a portion of the early-identified infants attended 12 years of regular school, universal screening would be cost-beneficial. A study comparing schooling costs in early-identified infants versus late-identified infants has not been done.

Is it feasible for rural states to implement a universal hearing screening program? Our study found infants could be successfully screened at a specified time rather than waiting for the infant to be perfectly quiet. Therefore, otoacoustic emission testing lends itself to being taken on the road, and the same equipment and personnel can be used to test infants at a number of hospitals within a 100-mile radius. The software is user friendly, and the cost of otoacoustic emission devices has dropped to approximately $7000. Wyoming began implementation of a universal hearing screening program in 1994, and as of 1998 that program has been fully implemented. In 1998, 95% of all infants born in Wyoming were successfully screened.²³ Universal hearing screening can be done, and has been done in rural states and communities.

Conclusions

Testing only high-risk newborn infants results, at best, in early identification of only half of the infants with hearing loss.¹ Universal screening is the only effective way to identify the majority of newborn infants with hearing loss. Early identification and treatment has been shown to significantly improve expressive and receptive language skills in infants and children with hearing loss. For this reason, it is clearly worthwhile to pursue universal screening. However, long-term patient outcomes and cost benefits should be studied.

Acknowledgments

We would like to thank the Children’s Miracle Network at Rapid City Regional Hospital, which provided funding of $13,562.50 to purchase the otoacoustic testing equipment.

We also thank Douglas A. Bright, MD, program director, Rapid City Regional Hospital Family Practice Residency, for his guidance and support with our project.