There is adequate data suggesting that the prevalence of permanent hearing loss in high-risk children could be as high as 40% of this high-risk cohort (Al-Muhaimeed 1996) and about 10% of all children bom will exhibit one or more of these indicators associated with hearing loss such as a history o f congenital hearing loss, very low birth weight (<1500g), congenital perinatal infection, congenital malformations of the head and neck, bacterial meningitis, severe neonatal asphyxia and hyperbilimbinaemia (White 1998; Kawarai et al 1999; Al-Muhaimeed 1996).
Because o f these reasons it has been a norm in developed countries to identify hearing loss in young children based on the high-risk indicators in the 1970s to early 1980s. The rationale for the high-risk register (HRR) approach was based on the fact that by focusing on a cohort of the population, which was at-high-risk, medical professionals would be able to use of auditory brainstem response in hospitals. Although such high- risk based screening programmes were the most frequent method used to identify hearing loss in very young children until late 1970s and early 1980s, an effective high-risk-based screening protocol would only identify 43-54% of all children with permanent congenital hearing loss in hospital based HRR in developed countries (White 1998; Kawarai et al 1999; Al-Muhaimeed 1996).
Another problem associated with the high-risk based screening programmes is the high dropout of parents. Mauk et al’s (1991) study reported high rates o f drop out of parents for diagnostic evaluations because it is difficult to motivate parents to return for the necessary diagnostic evaluations. For example, in Mahony and Eichwald’s (1987) and Mauk et al’s (1991) studies, which mailed and followed-up the selected parents and free diagnostic assessments were available at regional centres. Mobile vans also went to parents’ homes. Despite this effort only half o f the parents whose children were at risk attended an appointment and completed a diagnostic evaluation. There are many challenges affecting community-based as compared to institution based programmes especially when parents are not well informed of the benefits of completing the diagnostic procedures of screening programmes.
Fig. 2.1 adapted from Mahoney and Eichwald (1987) and White (1997) shows an example of screening programme evaluated to determine the compliance of parents
with identified as at-risk who were registered on a high risk register (HRR) screening programme in USA by Mahoney and Eichwald (1987).
Fig. 2:2 shows the problems of parental dropouts on the at-risk surveillance programme using birth certificates, based on high-risk registry to identity deaf children in Utah from 1978 to
1984 adapted from Mahoney and Eichwald (1987) and White (1997)
Live births: 283,298 Parental compliance: 12,699 (53%) Parental dropouts: 11,383 (47%) Sensorineural 101 (2%) Conductive 1,313(28%) Parents booked for
diagnostic evaluation: 7,445 (59%)
Parents who completed the diagnostic evaluation: 5,644 (72%)
Births with high risk factors: 25,564 (9%)
Parental dropouts: 1,801 (28%) Parents with no concerns:
5,254 (41%)
Adapted from:
• Mahoney and Eichwald 1987 (pp. 160).
• White (1997): (www.infanthearing.org).
Mahoney and Eichwald’s (1987) study, therefore concluded that only 22% o f the “at- risk” infants completed diagnostic evaluations hence 101 out o f 283,298 (0.36/1000) children were identified with sensorineural hearing loss. Despite the fact that physiological screens are used children identified, as at high-risk is comparably smaller numbers than those screened in universal programmes. The tests usually used to screen the registered high-risk children are the ABR or Transient Otoacustic emissions because they are the most reliably used protocols in evaluating audiological conditions in early infancy and would identify about 50% o f infants in efficient community programmes because of problems of parental breaking the appointments
for diagnostic evaluation and about 75-80% of hearing-impaired neonates in the intensive care (Mahoney and Eichwald’s 1987; White et 1998; White 1997; Kawarai et al 1999).
2.3.1 Screening protocols
Screening hearing loss in children is undertaken by using different types of screening tests, which depend on the precision of measurements, availability of the technology, the trained manpower and the purpose o f the screen. However, this field of audiometry divides hearing tests into two categories:
A) Physiological tests of which two screening protocols were reviewed, i.e. auditory brainstem response (ABR) and transient oto-acoustic emissions (TOAE).
B) Behavioural tests of which five screening protocols were reviewed i.e. pure- tone audiometry (PTA), home visitors distraction test (HVDT), picture and toy tests, simple clinical screening techniques and questionnaire screens.
Both types o f tests could be used either to screen or to diagnose hearing loss (Northern and Downs 1991; Haggard 1993; Kawarai et al 1999).
According to Northern and Downs (1991) and Haggard (1993) screening is an all- encompassing term, which could be defined as the preliminary acquisition of information for the early detection of a condition. More specifically, a hearing screen is a rapid and simple test and procedure, applied to a generally large population to identify individuals with a high chance o f having a hearing-impairment (Haggard, 1993). The concept of identifying a hearing-impairment before it is clinically apparent is an appealing public health consideration. Screening allows large numbers o f persons to be evaluated for a hearing problem with less commitment o f time, cost and inconvenience than with specific diagnostic tests (Hayes and Northern, 1996). For example, screening hearing loss in children is a fast procedure where a criterion of pass or fail is set, while diagnosis aims to determine the levels, types and possibly establish the aetiology of the hearing loss (Downs 1995). Two important considerations are understood in the above definitions:
• Screening hearing loss in children reveals a likelihood o f chance of hearing impairment rather than the certainty of accuracy of this condition.
• Therefore it is not an issue o f diagnosis and does not specify the type of deafness or severity of deafiiess.
It only separates individuals with high and low probability for a hearing-impairment. Persons identified with a positive outcome during the hearing screening procedure must be considered only ‘at-risk’ of the hearing loss until careful diagnostic testing can accurately determine the presence or absence o f this impairment (Hayes and Northern, 1996).