audiology and hearing health professionals in developed and developing countries audiology and hearing health professionals in developed and developing countries an audiologist, according to the american academy of audiology, "is a person who, by virtue of academic degree, clinical training, and license to practice and/or professional credential, is uniquely qualified to provide a comprehensive array of professional services related to the prevention of hearing loss and the audiologic identification, assessment, diagnosis, and treatment of persons with impairment of auditory and vestibular function, and to the prevention of impairments associated with them." according to the world health organization (who), approximately 250 million people worldwide have a disabling hearing impairment (i.e., moderate or worse hearing loss in the better ear). of these 250 million people, two-thirds live in developing countries. therefore, it is not surprising that "adult-onset hearing loss ranks 15th amongst the leading causes of the global burden of disease (gbd)." in order to learn more about a specific country, click the country of interest in the table below labeled "developing countries." prevention according to the world health organization, "half of all cases of hearing loss can be prevented through primary prevention. some simple strategies for prevention include: immunizing children against childhood diseases, including measles, meningitis, rubella and mumps; immunizing adolescent girls and women of reproductive age against rubella before pregnancy; screening for and treating syphilis and other infections in pregnant women; improving antenatal and perinatal care, including promotion of safe childbirth; avoiding the use of ototoxic drugs, unless prescribed and monitored by a qualified physician; referring babies with high risk factors (such as those with a family history of deafness, those born with low birth weight, birth asphyxia, jaundice or meningitis) for early assessment of hearing, prompt diagnosis and appropriate management, as required; and reducing exposure (both occupational and recreational) to loud noises by creating awareness, using personal protective devices, and developing and implementing suitable legislation. hearing loss due to otitis media can be prevented by healthy ear and hearing care practices. it can be suitably dealt with through early detection, followed by appropriate medical or surgical interventions." screening for hearing loss due to the lack of readably available hearing screenings in developing countries, hearing loss is often left undetected in all ages. reasons for the lack of hearing screenings is in part due to limited personnel and financial resources, according to mcpherson and olusanya (2008). hearing screenings are considered a high priority component of a hearing healthcare program in large due to the fact that early detection of hearing loss in infants can allow for prompt assessment, detection, and intervention of congenital and early onset hearing loss. furthermore, research has shown the importance of early intervention during the critical period of speech and language development (yoshinaga-itano et al., 1998). lastly, hearing screenings may be able to detect transient hearing losses that may dissipate with appropriate medical intervention. currently, actions have been taken in developing countries to prevent hearing loss. these actions include: promotion of immunization against known causes of hearing loss (e.g., measles, mumps, and rubella); improved care of mothers before and during child delivery; and education on the use or misuse of ototoxic drugs (mcpherson & olusanya, 2008). unfortunately, the healthcare systems in the majority of developing countries are unable to uphold these standards of care. definition and principles according to the world health organization (1971), screening is a "medical investigation that does not arise from a patient’s request for advice for specific complains. the term covers all types of examination and does not refer to their speed or accuracy." similarly harford et al. (1978) states, "screening is a process by which individuals are identified who may have disease or disorders that are otherwise undetected" and which many have "findings of asymptomatic cases" (haggard & hughes, 1991). when considering an appropriate screening program for a developing, or developed, country, wilson and jungner (1968) recommend the following ten basic principles that screening program should observe: "the condition to be screened for should be an important health problem there should be an accepted treatment for cases identified facilities for diagnosis and treatment should be available there should be a recognizable latent (early, asymptomatic) stage in the condition there should be a suitable test to employ in screening the test should be acceptable to the population the natural history of the condition should be understood there should be an agreed policy on whom to treat as patients the cost of case-finding (including diagnosis and treatment of those diagnosed) should be non-wastefully balanced in relation to expenditure on medical care as a whole case-finding should be an ongoing process and not a ‘one-off’ project." tools in developing countries, the predominant method of detecting children with hearing loss is through parental suspicion due to the child’s inappropriate response, or lack of response, to sound and occurs at a mean age of 22 months (gopal et al., 2001; mukari et al, 1999; olusanya et al., 2005). early detection of hearing loss requires reliable, valid, easy to apply, and safe hearing screening battery in order to be used in developing countries. a hearing screening is considered valid, according to mcpherson and olusanya (2008), "if it detects the majority of subjects with the target disorder (high sensitivity) and excludes most subjects without the disorder (high specificity) and if a positive test indicates the presence of the disorder (high positive predictive value)." two objective screening tests available for use in infants are otoacoustic emissions (oaes) and auditory brainstem response (abr). an oae is an electrophysiologic measure of the integrity of the outer hair cells in the cochlea. two types of oaes are transient evoked otoacoustic emissions (teoaes) and distortion product otoacoustic emissions (dpoaes). this test is relatively quick, non-invasive, and does not require the sleep or sedation. the oae screener results in either a pass or fail result, making it easy to read without requiring the screener to have audiological expertise. furthermore, oaes have a high sensitivity (>90%) and specificity (>96%) based on a two-stage screening (davis et al., 1997; jcih, 2000). disadvantages of oaes include its sensitivity to conductive hearing loss, which may occur within the first few days of life due to a vernix plug in an infant's ear canal, does not detect auditory neuropathy, and dpoaes may miss mild hearing loss. abr is an electrophysiologic measure of the function of cranial nerve eight and the auditory pathway in the brainstem. three electrodes are placed on the scalp in order to record electrical responses from auditory stimuli. recordings may be measured when the baby is sleeping, sedated, or in a quiet state. abr recordings are correlated with the degree of hearing loss, for click abr this range is from 1k to 4k hz within 10 to 15 db hl. the screening version of abr, or automated abr (aabr), is designed to produce a simple pass or fail result. aabr has high sensitivity (>90%), high specificity (>96%) and low positive predictive value (19%) (vohr et al., 2001; watkin, 2001). one advantage of aabr is that it is able to identify auditory neuropathy; however, the disadvantage is that aabr may miss mild sensorineural or exclusively low frequency hearing loss. therefore, it is recommended that hearing screening programs utilize a two-stage screening protocol that is made up of teoaes and aabr. combined, these two tests have the most favorable combination of specificity, sensitivity, acceptability and high coverage in hospitals with a wide range of birth rates (kennedy et al., 2000; vohr et al., 2001). mcpherson and olusanya (2008) write, "evidence from ongoing infant hearing screening programs has shown that these tests are acceptable to parents because they are not invasive, painless and quick to administer. they are currently employed in developed countries and in a growing number of developing countries." lastly, it is recommended that the two-stage screening protocol be performed on newborns prior to hospital discharge in order to decrease the number of infants lost to follow-up care. hospital-based hearing screening screening newborns in the hospital prior to discharge eliminates the need to ask parents to return specifically for their child to have a hearing test and allows healthcare professionals to satisfy an ethical obligation to ensure infants have been assessed for hidden abnormality prior to discharge. parents may be less likely to return to the hospital for an invisible and non-life-threatening disorder in their apparently normal newborn babies. in order to implement the two-stage screening protocol (i.e., teoaes and aabr), it is recommended the screening be entrusted to a dedicated team since adding this responsibility onto the nurses workload could result in few to none hearing screenings being performed since nurses may view this task as being less important compared to other routine clinical duties (mcpherson & olusanya, 2008). lastly, the two-stage screener should begin with teoaes followed by aabr for those referred from the first stage (i.e., teoaes). screening should occur has close to discharge as possible in order to minimize referral rates from vernix plugs. challenges faced in hospital-based screenings may include: excessive ambient noise causing higher referral rates; a long queue of babies may results on parents growing impatient and thus leaving prior to having their baby screened; and may fail to reach a significant number of newborns that are born outside of hospitals, which are common in developing countries (unicef, 2005). clinic-based hearing screening in developing countries, the majority of babies are born outside of hospitals (who, 2004) which causes a dilemma when developing hearing screening based in hospital settings. fortunately, "routine childhood immunization is perhaps the most well-established public health program globally, due to substantial technical/financial support it receives yearly from unicef, who and several donor agencies/partners" (mcpherson & olusanya, 2008). mothers with newborns, regardless of the birthing location, take their babies to immunization clinics at designated community health centers. immunization clinics have been used as platforms for delivering new child health intervention packages in developing countries (who, 2002) due their popularity derived from its known preventive value of preventing childhood deaths from killer disease and because it is offered free to parents. therefore, community-based hearing screenings may be performed in immunization clinics in hopes of reaching the newborn babies missed in hospital-based screenings. furthermore, lin et al. (2004), kapil (2002), and bantock and croxson (1998) speculate that hearing screenings may even be performed at infant welfare clinics and other child health programs. targeted or universal newborn hearing screening when considering universal newborn hearing screenings, an important ethical requirement is the delivery of equitable access to all babies. however, due to lack of resources in some settings and communities, a more targeted hearing screening approach may serve as a good take-off point for universal newborn hearing screenings. a targeted screening approach limits the screenings to babies who exhibit some risk factors for hearing loss. risk factors for hearing loss are provided below in the table titled, "risk factors for hearing loss in newborns (jcih, 2000)." targeted screening has been shown to identify approximately 50% of babies with moderate to profound hearing loss (vohr et al., 2000; watkin et al., 1991). unfortunately, this low number is due to the limitations of high risk factors either being difficult to detect at birth or during early childhood and lack of education of the high risk factors for hearing loss, especially in developing countries (derekoy, 2000; gray, 1989; minja, 1998). as mentioned previously, targeted screenings may be useful in establishing universal newborn hearing screenings in specific communities and educate communities on the predominant risk factors of hearing loss while establishing a more effective and culturally-appropriate universal hearing screening program. risk factors for hearing loss in newborns, according to the jcih, 2000, including: family history of sensorineural hearing loss. in-utero infections such as rubella, cytomegalovirus, syphilis, toxoplasmosis and herpes. craniofacial anomalies. birth weight less than 1,500g (3.3 lbs). hyperbilirubinemia at levels quiring exchange transfusion. bacterial meningitis. ototoxic medications. mechanical ventilation lasting 5 days or more. stigmata or other findings associated with a syndrome known to include a sensorineural and/or conductive hearing loss. birth asphyxia with apgar scores less than or equal to 5 at 1 minute or less than or equal to 6 at 5 minutes. school-based hearing screening in order to diagnose missed, progressive, or late-onset hearing loss, school-based hearing screenings are recommended in order to identify children with hearing loss. school-based screenings