Hearing Screening Overview
Sound has two measurable characteristics: frequency (Hertz) and volume (decibels).
Frequency (Pitch or Tone)
Frequency is the range of tones, measured in Hertz (Hz). Hertz is the international system of measurement (SI) unit of frequency or tone equal to sound wave or cycle per second. Although we can hear sounds as low as 20 Hz, we only use a very limited range (250 Hz through 8000 Hz) for our daily listening needs. Since this frequency range is critical for hearing and understanding speech and other sounds 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, and 6000 Hz (ages 11 and older) are used for routine hearing screening.
Volume (Intensity or Loudness)
Volume is the range of sound loudness, measured in decibels (dB). The greater the decibel number, the louder the sound. The minimal sound level that the majority of people with normal hearing can detect is 0dB. At least twenty percent of children can hear sounds as low as -10dB (Roberts & Huber, 1967). A 130dB sound causes pain in most people's ears. People usually speak at an intensity of 45-60dB (Centers for Disease Control and Prevention [CDC], June 2012).
Hearing and Hearing Loss Defined
The American Standards Association set the level of audiometric zero in 1951. Several studies in the 1960s found that about half of adults and children could hear the screening frequencies of 500, 1000, 2000 and 4000 Hz below audiometric zero (Roberts & Huber, 1967; Roberts & Bayliss, 1967). A person with normal hearing should be able to hear volumes as low as -10dB to 15dB and frequencies of 250 through 8000 Hz.
Hearing loss is when the softest or lowest decibel (16dB or more) someone can hear is louder than the sound (0 to 15dB) someone with normal hearing can hear. Refer to the Degree and Effects of Hearing Loss (PDF).
Hearing Loss Statistics
Hearing loss is one of the most common birth defects. Approximately one to three in 1000 infants are born with hearing loss (Dedhia, Kitska, Sabo, & Chi, 2013). In Minnesota, 259 babies were born in 2014 with hearing loss (Minnesota EHDI, 2015). During the 2015-2016 school year, Early Childhood Screening identified 3740 children in Minnesota ages three to five years as having potential problems with hearing (MDE, 2016). Six out of 1000 children have permanent hearing loss by age six (Choo & Meinzen-Derr, 2010). The incidence of hearing loss increases in the school age population to nine to 10 in 1000 (White, 2010). The incidence of fluctuating or temporary hearing loss in children is one in seven (American Academy of Audiology [AAA], 2011). Approximately 30 to 50 per 1000 youth have hearing loss by late adolescence (AAA, 2011).
Types of Hearing Loss
Hearing loss is either conductive or sensorineural and, depending upon the anatomical location of the loss, can be in the external, middle, or inner ear.
Conductive Hearing Loss
- Occurs in the external and/or middle ear.
- Blocks movement of sound into the ear.
- Is typically caused by: wax in the ear canal, a hole in eardrum, broken ossicles (middle ear bones), or middle ear fluid or infection.
- Can usually be treated medically or surgically; use of amplification devices such as hearing aids can help.
Sensorineural Hearing Loss
- Is a sensory problem in the inner ear, auditory nerve, or brain.
- Is the most common type of permanent hearing impairment.
- Causes include: genetics or damage to sensory nerves due to ototoxic drugs, infections, trauma, or noise.
- Is usually treated with amplification devices such as hearing aids or cochlear implants.
Combined Hearing Loss
- Involves both conductive and sensorineural hearing loss.
Causes and Effects
Causes of Congenital Hearing Loss
Results from hereditary or environmental influences before, during, or immediately following birth can cause congenital hearing loss. At least half of the causes of congenital hearing loss are associated with genetic risk factors (Kaye, 2006). The cause of about 25 percent of congenital hearing loss cases in the U.S. is unknown (CDC, 2012).
Causes of Acquired Hearing Loss
Acquired hearing loss occurs after birth, and may be temporary or permanent. Environmental infections or toxins are a common cause of infant and childhood hearing loss. Infections that can cause hearing loss include toxoplasmosis and cytomegalovirus. Ototoxic drugs that can cause hearing loss include aminoglycosides and cisplatin. Trauma to the head or ear can also cause hearing loss. Otitis media with effusion (OME), or fluid in the middle ear, is a common cause of temporary or fluctuating hearing loss. Ninety percent of children will have had OME at least once before school age (American Academy of Pediatrics [AAP], 2004). Five to ten percent of all children may have persistent OME for a year or longer. Children with persistent (chronic) OME are at risk of developing conditions that can cause permanent hearing loss.
Causes of Noise-Induced Hearing Loss (NIHL)
The effects of overexposure to loud noise can cause NIHL (CDC, 2008). NIHL can be temporary or permanent; it can result instantly from a single loud noise like a firecracker or gunshot, or can occur gradually from repeated exposure to noise. Approximately twelve and a half percent (5.2 million) of children six to 19 years of age have some level of noise-induced hearing loss (CDC, 2011). Sources of excessive noise for children include loud music, real or toy firearms, power tools, fireworks, loud toys, and loud engines such as those in snowmobiles, jet skis, motorcycles, or farm equipment (Montgomery & Fujikawa, 1992). NIHL prevalence increases significantly in late childhood and adolescence (AAA, 2011). Strong evidence exists that increases in high frequency NIHL in adolescents is the result of exposure to recreational noise. There is a wide variation in the reported incidence of NIHL in adolescents, as background noise can influence test results and make it difficult to assess.
Effects of Hearing Loss
Hearing loss affects language acquisition, speech, learning and psychosocial wellbeing. The critical time to stimulate the auditory and language brain pathways is during the first six months of life (Joint Committee on Infant Hearing [JCIH], 2007). Children with all degrees of hearing loss who receive appropriate intervention prior to six months of age can attain speech and language skills twenty to forty percent higher than their peers who receive intervention later and comparable to their hearing peers (JCIH, 2007).
A child with a hearing loss is at a greater risk for academic deficits. In school, students must be able to listen in a noisy environment, pay attention, concentrate, and interpret information. Unidentified hearing loss in the school population is associated with impairments in speech perception and social functioning, and difficulties in attention span and learning (AAA, 2011). Even mild hearing loss can significantly interfere with the reception of spoken language and educational performance. Reading success is especially dependent on the linguistic skill of interpreting information. Half of all children with hearing loss graduate from high school with a 4th grade reading level or less, unless appropriate early educational intervention occurs (Gallaudet Research Institute, 1996). In the case of NIHL, the effects of hearing loss may come on very gradually, depending on the amount of exposure to noise (Bess, Dodd-Murphy, & Parker, 1998, Daly, Hunter, & Giebink, 1999). Ongoing review of hearing and speech age-appropriate milestones, risk factors and routine hearing screening is critical for identifying hearing loss and optimizing educational outcomes (JCIH, 2007, AAA, 2011).
Joint Commission on Infant Hearing (JCIH) Position Statement (2007)
Principles and guidelines for Early Hearing Detection and Intervention programs
The JCIH 2007 Position Statement from the AAP identified 11 risk indicators associated with hearing loss. The identification of risk indicators is an essential component of a comprehensive hearing-screening program for infants and children. JCIH recommends that all infants and children receive an assessment of risk indicators for hearing loss during routine medical care, consistent with the AAP/Bright Futures Recommendations for Preventative Pediatric Health Care. This assessment for risk indicators includes information regarding prenatal/birth history, newborn hearing screening results, presence of specific early childhood conditions, and family risk factors (refer to the complete list). However, the use of risk indicators alone will identify only 40-50 percent of infants with hearing loss.
"Monitor all infants and children, with and without risk indicators, during routine medical care consistent with the AAP periodicity schedule. Refer all infants with a risk indicator for hearing loss to an audiologist at least once by 24 to 30 months of age. MDH recommends that an audiologist assess infants and children with risk factors as soon as a concern is identified. Children with risk indicators that are highly associated with delayed-onset hearing loss, such as having received ECMO or having CMV infection, should have more frequent hearing assessments (JCIH 2007)."
Explanation of Risk Indicators
To assist in obtaining accurate and pertinent information from each parent or caregiver, a brief explanation of JCIH risk indicators associated with permanent congenital, delayed
- Caregiver concern regarding hearing, speech, language, or developmental delay
Most parents are reliable reporters of their child's development. Depending on the setting and the concern, parents have been accurate found to be accurate up to 94 percent of the time (Glascow & Dworkin, 1995).
- Family history of permanent childhood hearing loss
Hereditary (genetic) hearing loss in both maternal and paternal family members, living and deceased is an important risk factor for congenital hearing loss (JCIH, 2007). Absence of a family history of genetic or risk factors for congenital hearing loss does not rule out a genetic cause. Depending on risk factors, the child may need regular follow-up with an audiologist. It is important to determine whether the relative has acquired hearing loss (such as that resulting from meningitis, noise exposure, chemotherapy, or the aging process); acquired hearing loss is not an inherited condition.
- Neonatal intensive care for more than five days, or any of the following: extra-corporeal membrane oxygenation (ECMO), assisted ventilation, exposure to ototoxic medications (gentamycin and tobramycin) or loop diuretics (furosemide also known as Lasix), or hyperbilirubinemia that requires exchange transfusion
Infants admitted to the NICU are at greater risk for hearing loss. For example, infants with very low birth weight are at increased risk of both sensorineural and conductive hearing loss. Jaundice is a condition, which occurs when there is too much bilirubin (by-product from the liver) in the blood. High bilirubin levels (hyperbilirubinemia) requiring an exchange transfusion can be ototoxic and may cause hearing loss. Premature infants and infants with low birth weights are at a greater risk for high bilirubin levels. Low bilirubin levels (slight jaundice) typically do not affect hearing. In addition, infants who require prolonged use of mechanical ventilation are at risk for hearing loss (e.g. persistent pulmonary hypertension, conditions requiring the use of extracorporeal membrane oxygenation [ECMO]) (JCIH, 2007).
Ototoxic: Refers to conditions and medications that have the potential to damage the cochlea, auditory nerve and sometimes the vestibular system of the ear. Conditions include persistent pulmonary hypertension and hyperbilirubinemia. Ototoxic drugs include antibiotics such as aminoglycoside gentamicin, loop diuretics such as furosemide. Use of ototoxic medications can result in sensorineural hearing loss, equilibrium disturbances, or both. Either may be reversible and temporary, or irreversible and permanent (Weichbold, V., Neckahm-Heis, D., & Welzl-Mueller. 2006).
- In utero infections, such as cytomegalovirus (CMV), herpes, rubella, syphilis, or toxoplasmosis
The majority of infections in pregnant women are not known to cause hearing loss. However, some infectious agents, contracted by the mother during pregnancy, may cross the placental barrier and infect fetal tissue. Teratogenic (birth defect causing) infections can be associated with hearing loss, especially those occurring during the first trimester, since this is when the auditory system develops. Many infections go unrecognized due to the lack of clinical symptoms in the mother. The infant may have a normal NHS and not be identified as at risk for hearing loss. Hearing loss in children has been linked to the following infectious agents.
CMV: This herpes virus is the leading cause of fetal viral infection in the U.S. (CDC, 2013). This infection is most often asymptomatic in the mother (Fowler et. al, 1997). CMV can cause sensorineural hearing loss, which varies in severity, may have a delayed onset, may be unilateral, and is often progressive.
Herpes: Either systemic or simplex, type one or two, are in the same family as the CMV virus. Herpes may cause severe to profound sensorineural hearing loss (al Muhaimeed & Zakzouk, 1997).
Toxoplasmosis: Is an infection caused by a protozoan parasite and is usually asymptomatic in the mother. A fetus is most likely to be affected by a first trimester infection. Frequently seen effects of toxoplasmosis include sensorineural hearing loss (Andrade et al., 2008), as well as mental retardation, seizures, and ocular disease.
Rubella (German measles): Effectively eliminated in the U.S, rubella is still endemic in other parts of the world (CDC, 2012). Rubella poses a serious risk to the developing fetus when a maternal infection occurs within the first trimester of pregnancy. Hearing loss is the most common rubella-related birth defect; other anomalies may include heart disorders, low birth weight, mental retardation, and vision loss. When hearing loss occurs, 50 percent of children have bilateral severe to profound loss. This type of hearing loss may be progressive.
Syphilis: Congenital syphilis may become apparent in the first two years of life, or between the ages of eight to 20 years. Hearing loss is sensorineural and maybe be sudden, progressive, or temporary.
- Craniofacial anomalies, including those that involved the pinna, ear canal, ear tags, ear pits, and temporal bone
Craniofacial abnormalities (e.g. cleft lip/palate, shortened neck, webbed neck, abnormal head circumference) may be indications of the presence of hearing loss. Malformation of the ears may include atresia (close or narrowing of the ear canal), low set ears, skin tags, and preauricular pits. These abnormalities may be indicative of a syndrome associated with hearing loss (Weichbold, V., Neckahm-Heis, D., & Welzl-Mueller. 2006).
- Physical findings such as a white forelock that are associated with a syndrome known to include a sensorineural or permanent conductive hearing loss
- Syndromes associated with hearing loss or progressive or late-onset hearing loss, such as neurofibromatosis, osteopetrosis, and Usher syndrome; other frequently identified syndromes include Waardenburg, Alport, Pendred, and Jervell and Lange-Nielson
Many syndromes that include observable physical anomalies of the head, neck, and ears such as Down syndrome and neurofibromatosis type II (NF2), frequently result in hearing loss. Some syndromes are not evident at birth.
- Neurodegenerative disorders, such as Hunter syndrome, or sensory motor neuropathies, such as Friedrich ataxia and Charcot-Marie-Tooth syndrome
- Culture-positive postnatal infections associated with sensorineural hearing loss, including confirmed bacterial and viral (especially herpes viruses and varicella) meningitis
- Head trauma, especially basal skull/temporal bone fractures that requires hospitalization
Head trauma (e.g. a skull fracture) may result in conductive or sensorineural hearing loss due to damage to the middle ear, cochlea, or auditory cortex. Conductive hearing loss may occur due to perforation of the tympanic membrane, bleeding, or disruption of the ossicles. Sensorineural loss may occur due to damage or obliteration of the temporal bone housing the inner ear (Fitzgerald, 1996; Podoshin & Fradis, 1975).
Some medications used to treat cancer, such as cisplatinum, can be ototoxic.
Note: The 2007 JCIH Position Statement no longer includes in its list of risk indicators recurrent or persistent otitis media (OME) with effusion for at least three months. However, the JCIH recommends careful assessment of middle-ear status at all well-child visits, and referral of children with persistent middle-ear effusion (OME) lasting three months or longer for a hearing evaluation. Monitor OME vigilantly as it compounds hearing loss due to other conditions (e.g. sensorineural hearing loss).
Noise-Induced Hearing Loss (NIHL)
Noise-Induced Hearing Loss (NIHL) (PDF)
About 12.5 percent of children and teens have lasting hearing loss from contact with very loud noise (Sight and Hearing Association, 2013).
Why does loud noise cause hearing loss?
There are 15,000 to 20,000 tiny cells (cilia) in the inner ear that send sounds to the brain. Hearing loss can result when these cilia are damaged. To picture what happens when these cells are exposed to too much noise, think about when you walk on fresh grass. When you walk on it lightly only a few times it bounces back to its original shape. If you walk on grass often, or you crush it, it becomes matted down and will not bounce back. Exposure to sounds that are loud enough or occur long enough can damage the ears' cilia so that they can no longer bounce back into shape and can no longer send sound to the brain. This is the cause of noise-induced hearing loss (NIHL). Frequency is the tone of a sound. The frequency of a sound can range from very low to very high tones. At first, NIHL can make it hard to hear high tones. This can cause problems hearing speech sounds like "s". Background noise often makes hearing these sounds even harder to hear. NIHL slowly progresses into lower tones. Once these are affected, you may have problems hearing people when they speak.
What kind of noise is too loud?
The noise is too loud if you have to raise your voice to talk to a person who is only an arm's length away. The loudness of sound is measured in decibels (dB). Noise over 85dB can cause hearing loss. Hearing noise louder than 110dB for more than one minute can cause lasting hearing loss. Instant damage to hearing can be caused by sounds 150dB or higher. For every 5dB increase in sound level, it takes 50 percent less time to get hearing loss (Sight and Hearing Association, 2013).
|Examples of Excessive Noise:
Max Time Allowed Without Earplugs
|Guns||120dB +||7.5 minutes|
|Rock concert||120dB||7.5 minutes|
|Stereo Headphones||110dB||30 minutes|
|Boom box||110dB||30 minutes|
|Lawn mower||90dB||4 hours|
*Note: Decibel levels vary between sources, though the levels noted here are generally agreed upon in the field.
How can I prevent NIHL?
- Know how to avoid loud noise and protect your ears.
- Know which noises cause damage (those about 90 decibels).
- Wear earplugs or other hearing protective devices when involved in a loud activity. Special earplugs and other ear protectors are available at hardware stores and sporting goods stores.
- Do noisy activities for a short time and then do something quiet to rest your ears.
- Be alert to noise in the environment.
- Tell your friends and family about this!