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Hearing impairment among ‘at risk’ children
INTE.WATMALIOURNALOF
International Journal of Pediatric Otorhinolaryngology
ELSEVIER
34 (1996)
75-85
Hearing impairment among ‘at risk’ children Hamad S. Al-Muhaimeed* Drpartmrnt of Otorhinolaryn~ology, King Abdul Azi: Urtitxrsit~* Hospital. P.O. Box 24.5,Riyudlr 1141. Saudi Arubiu Received 18 October
1994: revision received 9 June 1995; accepted 12 June 1995
Abstract A survey was carried out to identify the prevalence and the aetiology of hearing impairment among infants and children at risk based on the criteria. Out of 6421 surveyed children, 1256 (19.6%) were found ‘at risk’ for hearing impairment. Children with hearing impairment in this study were found to be 494 which represent 39.3% of the ‘at risk’ children. We found 326 (66%) children had conductive hearing loss almost all associated with secretory otitis media (n = 232). Sensorineural hearing loss affected 168 (34%) children. Heredo-familial causes were responsible for about 111 (66.1%) cases. The detailed causes of conductive and sensorineural hearing loss are presented and compared with other studies in the literature. Conductive hearing impairment was mild in the majority of the cases n = 27 1, (83X), moderate in 55 (17%) cases. Sensorineural hearing loss was mild in 113 (67,3X), moderate in 32 (19%) and profound in 23 (13.7%) cases. A large scale Kingdom-wide study to focus on aetiology of deafness among Saudi infants and children to find out the extent of this problem is recommended. Keywords: Sensorineural hearing loss; ‘At risk’ child; Consanguinity
1. Introduction Hearing is necessary to learn language and speech and the development of the baby is highly dependent upon hearing, and the social, emotional and intellectual
development is bound up with the normal functioning of the auditory system. Ewing and Ewing (1950) [7] have described in detail the effect of a hearing disability * Corresponding author Ol65-5876/96/$09.50 0 1996 Elsevier Science Ireland Ltd. All rights reserved SSDI 0165-5876(95)01254-Z
16
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/ Int. J. Pediatr. Otorhinolaryngol.
34 (1996) 75-85
on a developing child, as well as the importance of hearing on physical attributes of breathing, a sense of rhythm, walking, eating, drinking and personal habits. Hearing impairment during infancy and childhood has its greatest effect on language development and even a mild loss can interfere with the natural growth. Therefore, early detection and intervention will minimize the effect of such disability. In order to guarantee the earliest possible identification of hearing impairment, hearing screening of all the neonates has been advocated [4]. However, the results of mass screening programs were found to be inconsistent, misleading and unnecessarily expensive [3]. The Joint Committee of Infant Hearing and Screening (1982) [lo] recommended that infants at high risk for hearing impairment should be identified by means of history and physical examination. The Infant High Risk Register lists the following factors: 1. A family history of hearing impairment; 2. Congenital perinatal infection; 3. Anatomic malformations of the head and neck; 4. Low birth weight ( < 1500 g); 5. Hyperbilirubinemia; 6. Bacterial meningitis; 7. Severe neonatal asphyxia. After identifying the high risk infants and children, they are subjected to screening tests. Those children who fail the screening tests are then referred for full diagnostic tests which vary according to the age, co-operation, mental condition facilities available, etc. Using the above criteria, this study aims at identifying the aetiological factors of hearing impairment in high risk infants and children using full diagnostic hearing evaluation including appropriate laboratory investigations. This is the first study of its type in Saudi Arabia on the epidemiology and possible aetiology of deafness. 2. Materials
and methods
A comprehensive survey of 6421 Saudi infants, pre-school and school-age children from 2 months up to 12 years was carried out in Riyadh in the period between May 1988 and September 1990. The sampling design was essentially based on quota sampling using two interlocked quota controls, age and sex. On the other hand, in order to have an adequate and representative coverage of all socio-economic and demographic groups of the residents of Riyadh, it was necessary to introduce an element of randomness during the actual sample selection process. Therefore, a stratified three-stage random sampling frame of Riyadh administrative areas and roads was established as follows: A field work was carried out to enumerate and number the administrative areas and roads of Riyadh. This field work included the outlining of administrative areas and dividing them into roads. It was decided to use the method of areas and roads
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for sample withdrawing to facilitate data collection. It was decided not to use methods of sampling by aerial maps, though in theory, it is an excellent method. However, for the city of Riyadh, there would have been some difficulty in identifying segments inside each area by using a grid map because the segments are not numbered and there are no names for the land marks which would have helped in outlining boundaries of the segments. Road locations were adopted because this was easier each road has a number and there were marks which indicated the road limits on both sides. The sample withdrawing could be summarized as follows: 1. Riyadh was divided into 93 administrative areas (Table 1). They were further divided into six strata according to socio-economic homogeneity; 2. In each stratum the number of areas were identified and one fifth of the areas in each stratum were chosen randomly to be included in the study as presented in Table 1; 3. Each randomly selected area was further subdivided into roads, altogether, there were 1376 roads in the 17 randomly selected areas. One-sixth of the roads in each of the 17 areas selected for the first stage of the study was chosen randomly. Two-hundred-and-twenty-four roads were randomly selected for the study; 4. Each road was subsequently divided into smaller manageable blocks of approximately equal size and samples of such blocks were randomly selected. 2.1. Field survey design und procedures jbr dmt collection Within each block selected, a random starting point was chosen and each survey team was asked to follow a pre-determined zigzag route calling at every other household encountered. There were two survey teams. Each survey team included an E.N.T. specialist, a nurse, a social worker, a field supervisor and a driver. The teams established whether there were any children in the household. If so, and after obtaining permission from the family. the team proceeded to the clinical examination of the child and completed the relevant questionnaire with the mother. In order to meet the required quotas, daily records of contacts were submitted to the field supervisors who were responsible for co-ordinating the field operations. Table I Total number of administrative areas of Riyadh and areas surveyed according respect to socio-economic status
to homogeneity
with
Stratification according to homogeneity with respect to socio-economic status
Total # of areas in each socio-economic stratum
No. of areas sampled for the survey (I 5 of areas from the total number of areas in each socio-economic stratum)
Stratum Stratum Stratum Stratum Stratum Stratum
Only Only Only Only Only Only
Only Only Only Only Only Only
Total
I 2 3 4 5 6
93
6 areas I2 areas I6 areas I5 areas 7 areas 37 areas
I7
I 2 3 3 I 7
area areas areas areas area
areas
78
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A number of interviews, anthropometric measurements and clinical examinations were also carried out in the Well-Baby Clinics and Maternal-Child Health Centers which had been previously randomly selected. This sampling procedure, had four major advantages: 1. Randomness of the study sample; 2. Control over the sample size in each age group in order not to exceed the required number in each age and sex group, or fail to reach the required number. Since there is a predominance of children below the age of 6 years, we decided the proportion of children < 6 years not to exceed 2:l to those over 6 years; 3. Manageability of the implementation of the task in terms of time and resources allocated for the completion of each age group in the survey; 4. Precise estimation of children’s age and other related data. 2.2. Study procedure
In various city blocks, individuals who were ‘at risk’ for hearing impairment were determined by the presence of one or more of the following: 1. History of genetically-determined childhood hearing impairment; 2a. Identification of the etiological agents of congenital infection: TORCH agents (e.g. toxoplasma, syphilis, rubella cytomegalovirus, herpes); 2b. Identification of the aetiological agent of chronic otitis media or secretory otitis media which may attribute to hearing impairment; 3. Rubella or other non-bacterial intrauterine foetal infection (e.g. cytomegalovirus and herpes infection); 4. Defects of the ear, nose or throat. Malformed, low set or absent pinnae, cleft lip or palate (including submucous cleft); any residual abnormality of the otorhinolaryngeal system; 5. Prematurities or birth weight < 1500 grams; 6. Cyanosis; 7. High bilirubin concentrations that exceed the level necessaryfor blood transfusion. The first draft of the research protocol was tested during an initial 3 month pilot phase and was further modified according to the analysis of pilot data and assessment of the epidemiological and statistical co-ordinators of the research program. 2.3. Data processing and analysis
All completed research protocols were submitted to the project methodological unit each day and were edited on a daily basis to ensure that possible errors could be immediately identified and corrected. The data was then processed by a computer using statistically package for biomedical sciences(BMDP) every 6 months. All the infants and children who participated in the study were exposed to full ORL clinical examination after taking a detailed history from their parents including social and family history. Hearing of children below 6 years were evaluated by brain stem evoked response (Type Amplaid MK15) and older children were
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Table 2 Age and sex distribution of ‘at risk’ children Age group
Number
Male
Female
I6 years 6612 years
831 (66.2%) 425 (33.8%)
514 (61.9%) 276 (65%)
317 (38.1%) 149 (35%)
Total
1256 (100%)
790 (63.0%)
466 (37.0%)
evaluated by pure tone audiometry (Type GSI 10) Tympanometry was done on all children. Tympanometry does not evaluate hearing levels, but may give information on the topical site of a hearing lesion. Appropriate blood specimens were collected and sent to the laboratory to allow identification of the aetiological microbiological agents. The assay performed included IgG, IgM antibodies to TORCH agents which were tested for by an enzyme immunoassay using Virgo, ELISA reagents and automated Virgo equipments Model 400AT. The tests were carried out according to the instructions of the manufacturers. Appropriate positive and negative controls were used. Positive IgM antibodies specific to any of TORCH agents or a fourfold rise in specific IgG antibody titre were considered a potential aetiological agent for hearing impairment. 3. Results
Out of a total of 6421 infants and children 1256 (19.56%) were identified as ‘at risk’ for hearing impairment. Table 2 shows the distribution by age and sex of the ‘at risk’ children. About two third (63%) were males and a third (37%) were females. Two-thirds (66.2%) of the participants were 6 years and below whereas the remaining were older than 6 years. The number of children with hearing impairment were found to be 494 which represent 39.3% of the ‘at risk’ children (Table 3). Three-hundred-and-twenty-six children were suffering from different degrees of conductive hearing loss (Table 3) which forms 26% of the ‘at risk’ group. Most of the casesof conductive loss (232) were due to secretory otitis media (Table 4). Table 3 Types of deafness among ‘at risk’ children Number Bilateral sensorineural hearing loss Unilateral sensorineural hearing loss Familial progressive sensorineural hearing loss Mixed hearing impairment Conductive hearing impairment Undetermined
61 13 26 54 326 8
Total
494
Percent of the risk group 5.3 1.0 2.1 4.3 26 0.6 1256
80
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34 (1996) 75-85
Table 4 Causes of hearing impairment Causes
Number
1. Secretory otitis media 2. Suppurative otitis media 3. Heredo-familial and consanguinity 4. Mumps 5. Meningitis 6. Rubella 7. Low birth weight 8. Down’s syndrome 9. Unknown (sensorineural hearing loss)
232 94 III 4 I5 4 17 2 15
Total
494
Percentage 47.0 19.0 22.5 0.8 3.0 0.8 3.4 0.4 3.0 100
One-hundred-and-sixty-eight had sensorineural hearing loss which represent 34% of all children with hearing loss. The different causes of hearing loss are given in Table 4. Secretory otitis media is the commonest cause of conductive hearing loss affecting 47% of children with hearing impairment. This is followed by suppurative otitis media (19%). On the other hand, the commonest cause of sensorineural is heredo-familial causes affecting 111 (22.5%) children and infants and this represents 66.1% of all cases of sensorineural deafness. Other causes were due to prematurity (3.4%) meningitis (3.0%) rubella (0.8%) mumps (0.8%) and Down’s syndrome (0.4%). Fifteen cases (3.0%) were classified as of unknown causes. Conductive hearing loss was mild in the majority of the cases, n = 271 (83%) moderate in 55 (17%) cases (Fig. 1). Sensory neural hearing loss was mild in 113 (67.3%) moderate in 32 (19%) and profound in 23 (13.7%) cases(Fig. 2). 4. Discussion
The number of children considered to be ‘at risk’ of hearing impairment were found to be 1256, about one fifth of all the surveyed children (6421). It is known that the details of ‘at risk’ registers vary from place to place with consequent variation in efficiency in detecting deafness and to be effective, an ‘at risk’ register must have a prevalence rate of 14 times greater than the general population [16]. The number of children with hearing impairment in this study were found to be 494 (39.3%) of the ‘at risk’ children. The very high prevalence of deafness(39.3%) among the at risk group is striking. This could be due to the efficiency of detecting the minor degreesof conductive and sensory neural hearing loss using objective diagnostic tests; but further investigation is needed to reach firm conclusions about the efficiency of our criteria of the ‘at risk’ register. The number of casesof conductive hearing impairment was 326 (26%) (Table 3) of all surveyed children and the majority (n = 232) were due to secretory otitis
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media (Fig. 1). The epidemiology of such disease is poorly documented and shows wide variation according to the geographical location, age and methods of identification. The prevalence of middle ear effusion varies from 8.7% (reported by Suarez Nieto et al., 1983) [17] among Spanish children aged from 2 months to 12 years; to 50% prevalence reported by Brooks (1976) [5] in children aged 557 years in the UK. Our study’s relatively low prevalence of 18.5% may be due to the age distribution of the sample, the seasonal variation or actual low prevalence of such a disease. Suarez Nieto et al. (1983) found the prevalence of secretory otitis media decreased with increasing age from 38.8% at 2 years to 1.1% at 11 years. The number of sensorineural hearing loss caseswas 168 (13.4%) of all surveyed children (Fig. 2). This figure is higher than the prevalence of 1.1- 1.7% reported by others [8,9] and reflects the importance of sensory neural hearing impairment as a major health problem in Saudi Arabia in comparison with other parts of the world. When analysing the different underlying causes of sensorineural deafness, hereditary hearing impairment was found to be the most common single cause, being established in 111 cases, which represent 66.1% of all cases of sensorineural deafness. Again, this represent a significantly higher prevalence than other reports approximately one half of sensorineural hearing loss in children was attributed to hereditary causes [14,15]. Also, the prevalence of hereditary deafness (1.7% of the total number) is markedly higher than the prevalence of 1 in 2000 to 1 in 6000 live birth given by other authors. This high prevalence of hereditary deafness may be explained, in part, by the widely practiced consanguinity in Riyadh. The high prevalence of consanguinity in Saudi Arabia is evident from this study. First cousins was found in 22.1% of the parents and more distant consanguinity was present in another 23% (Table 5). It is estimated that 75.9% of hereditary hearing loss is caused by single gene recessiveautosomal transmission [lo]. Consanguineous marriage increases the chance that the two parents may each have the same recessive gene inherited from their common ancestor and this increases the
oderate
conductive
Mild conductive hearing ,109~ n = 271 Fig. 1. Hearing severity of children with conductive
hearing loss (n = 326).
82
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/ Int. J. Pediatr. Otorhinolaryngol.
oderate
34 (1996) 75-85
SNHL
Profound
SNHL
Mild SNHL n 113 q
Fig. 2. Hearing severity of children with sensorineural
hearing loss (n = 168).
proportion of homozygotes, at the expense of heterozygotes. On the other hand a consanguineous marriage also increases the risk of transmission of polygenic (multifactorial) inheritance which may play a minor role on the transmission of some casesof hereditary deafness. The efficiency of detecting genetic deafness may play a part in the increase in cases of hereditary deafness in some earlier studies, including the current survey. Taylor et al. (1975) [18] reported that most, if not all, casesof deafness previously classified as of ‘unknown cause’ are casesof autosomal recessive inheritance. The hereditary deafness may appear at the time of birth or may be delayed developing after birth. The diagnosis of hereditary deafnessis usually based on careful study of the family, pregnancy, birth and infancy history and by careful physical examination of the affected individual and other family members in addition to the necessary laboratory work. Low birth weight was found to be the second commonest cause of sensorineural hearing loss among the children in the current study. Children born with low birth weight accounted for 10.2% (n = 128) of the participants. Seventeen children of those were found to have sensorineural hearing loss primarily caused by the low birth weight itself (after excluding children exposed to other aetiological factor of Table 5 Consanguinity Parent’s relation First cousins Relatives Not relatives Total
of parent (n = 1256) Percent 21.1 23.0 55.9 100.0
H.S. Al-Muhaimeed
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83
deafness). These data mean that 13.3% of the low birth weight children suffered from deafness directly attributed to the low birth weight and also mean that low birth weight accounted for 10.1% of the childhood sensorineural deafness. This relatively low frequency in our study is probably due to the exclusion of low birth weight children who have been exposed to other causative factors of childhood deafness, particularly asphyxia and jaundice. It is worth noting that deafness among low birth weight infants has been attributed to several factors, such as the ‘immaturity’ the use of ototoxic drugs, the ambient noise of the incubators in which these infants were nursed and the presence of some perinatal complications (e.g. hypoxia, acidosis) that are likely to produce brain damage and which are more frequently encountered among low-birth-weight infants [ 1,2]. Meningitis as a cause of a sensorineural deafness was shown in 15 cases (8.9%) of the 168 children with sensorineural hearing loss. Several studies of school age children in different parts of the world have shown that bacterial meningitis is the cause of 8-24% of all cases of severe deafness [12]. Post-meningitis sensorineural hearing loss may be unilateral or bilateral and may be partial or complete. The incidence of partial hearing loss in the literature ranges between 20 and 70% [12]. Post-meningitis deafness is unilateral in 20-60% of cases [11,13]. Since no specific therapy can be recommended to diminish the incidence of sensorineural deafness following meningitis, prevention of meningitis is the only means to reduce such a serious complication. Vaccination against the three most common causes of bacterial meningitis are now available and their use should be encouraged. Four cases (2.4%) of the sensorineural deafness are attributed to maternal rubella. This relatively low incidence is in contrast to the findings of Martin (1982) [l l] who found rubella to be the commonest identifiable cause of congenital sensorineural deafness (25%) in children of the European Community. In contrast to the common belief, rubella at any stage in the pregnancy can cause deafness. Nowadays the laboratory diagnosis of congenital rubella may be established by: the isolation of rubella virus from urine or throat cultures during the first week of life: the identification of IgM antibodies against rubella in serum from the neonate; and an increasing antibody titre to rubella virus in an infant during the first few months of life [6]. The sensorineural hearing loss encountered in these cases is usually severe to profound. Screening and vaccination programmes have markedly reduced the incidence of congenital deafness due to rubella. Mumps accounted for four cases (2.4%) of sensory neural hearing loss. Hearing loss associated with mumps occurs in about 5 of every 10 000. Deafness is usually unilateral and profound. Mumps is probably the most common cause of unilateral acquired sensorineural hearing loss in children [l4]. The number of children with sensorineural hearing impairment classified as of unknown cause was 15, representing 8.9% of all cases with hearing impairment. In many earlier reports approximately 30-35% of the cases are placed in a category of ‘unknown cause’ [ll]. Many authors believe that most cases of deafness of undetermined causes are cases of autosomal recessive inheritance [g]. A follow-up of those children may reveal additional pertinent information which may be instrumental in determining the cause of deafness. Feinmesser et al., 1986 [g]
84
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34 (1996) 75-85
followed 44 deaf children of unknown cause (representing 41.4% of 107 deaf children) and were able to determine the cause of deafnessin 12 of them. Therefore, the percentage of the group with unknown aetiology dropped from 41.4 to 28% in their series. 5. Recommendations 1. To carry out a large scale Kingdom wide study to find out what is the extent of this problem in the Kingdom of Saudi Arabia. 2. AS this study has indicated that consanguineous marriage is prevalent in the Kingdom, a comprehensive genetic study should also be carried out in order to find out the heredo-familial aetiology of deafness and its magnitude. 3. Since early diagnosis is essential for the successful treatment and the proper development of speech, all babies should undergo screening tests for hearing around the age of 6 months. This is in view of the fact that there is no existing policy to such screening. In the management of the children with hearing impairment it is crucial to take into consideration that the ability to learn auditory discrimination diminishes, as the child grows older. In this respect it is important to appreciate that the first year of life is the most crucial time for having normal hearing. Accordingly, the child with hearing impairment should be taught to hear as early as possible. As far as hearing aid is concerned, it should be fitted at the earliest ages; this often being at ages as young as 10 months when the child will accept it and does not pull it out. 4. Since total deafness is quite rare and only l-2% of deaf children have no hearing at all, all children with hearing impairment should have a 2 year auditory training before being regarded as totally deaf. Family guidance should start from the day hearing impairment is diagnosed, being undertaken by an audiologist and by the specialist teacher of the deaf. The teacher should train the mother of the hearing impaired child on how to handle her child so as to bring sound to him or her. 5. Hearing impairment is a preventable ailment especially when it is due to inflammatory causes such as otitis media. In the current study 66% of the children with hearing impairment had otitis media making it the major cause. Furthermore, 22.5% of the hearing impairment in this study were due to hereditary causes mainly due to consanguineous marriage. Therefore, early detection of infection and family counselling could be most effective in preventing hearing impairment in Saudi Arabia. Acknowledgement I would like to thank King Abdul Aziz City for Science and Technology (KACST) for sponsoring this study; Prof. Siraj M. Zakzouk for his great support and Ms. Connie Unisa for her secretarial work.
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References [i] Adam, D.A. (1987) Causes of Deafness, Scott-Brown’s Otolaryngology, Vol 6 (5th ed.) Butterworths, London, pp. 35-51. [2] Angnostakis, D., Petmezakis, J., Papazissis, G., Messaritakis, J., Matsaniotis, N. (1982). Hearing loss in low birth weight infants. Am. J. Dis. Child. 136, 6022604. [3] Barr, B., Stensland, Junker K. and Svard, M. (1978) Early discovery of hearing impairment: a critical evaluation for the BOEL test. Audiology 17, 62. [4] Bhattacharya, J., Bennet, M.J. and Tucker, SM. (1984) Long terms follow-up of newborns tested with the auditory response cradle. Arch. Dis. Child. 59, 5044511. [5] Brooks, D. (1976) School screening for middle ear effusion. Ann. Otol. Rhino]. Laryngol. 85 (suppl. 25), 2233229. [6] Davis, L.E. and Johnson, L.G. (1983) Viral infections of the inner ear: clinical virologic and pathologic studies in humans and animals. Am. J. Otolaryngol. 4, 3477362. [7] Ewing, I.R. and Ewing, A.W.G. (1950) Opportunity and the Deaf Child. London; University of London Press Ltd. [8] Feinmesser, M., Tell, L. and Levi, H. (1986) Etiology of childhood deafness with reference to the group of unknown cause. Audiology 25, 65-69. [9] Harrison, K., Watson, T. (1979) Deafness in Children. In: Scott Brown, Diseases of the Ear, Nose and Throat, Vol. 2 (4th ed.) Butterworths, London, pp. 395-417. [IO] Joint Committee on Infant Hearing (1982) Joint Committee Statement on Infant Hearing Screening. Paediatrics 70 4966497. [I I] Martin, J.A.M. (1982) Etiological factors relating to childhood deafness in the European Community. Audiology 21 1499158. [I21 Nodal, J. (1978) Hearing loss as a sequela of meningitis. Laryngoscope 88, 739-755. [13] Nylen, 0. and Rosenhall, U. (1979) Haemophilus influenzae, meningitis and hearing. Int. J. Pediatr. Otolaryngol. I, 97- 101. [I41 Paparella, M.M. and Schachern P.A. (1991) Sensorineural Hearing Loss in Children. In: Paparella, M.M. and Shumrick, D.A. (Eds.), Otolaryngology, W.B. Sauders Company Vol. 2, Philadelphia, pp. 1579. [15] Smith, R.J.H. (1988) Medical Diagnosis and Treatment of Hearing Loss in Children In: Cummings, C.W. (Eds.) Otolaryngology Head and Neck Surgery, C.V. Mosby Company, Vol. 4, St. Louis, pp. 322553246. [16] Snashall, S. (1988) Deafness in Childhood. In: Ludman H. (Eds.), Mawson’s Diseases of the Ear, Fifth Edition. Edward Arnold, London, p. 226. [17] Suarez Nieto, C., Mallaguiza, Calvo R. and Barthe Garcia P. (1983) Etiological factors in chronic secretory otitis media in relation to age. Clin. Otolaryngol. 8, 171-174. [ 181 Taylor, I.G., Brasier, V.J., Hine, W.D., Chiveralls K. and Morris, T. (1975) A study of the cause of hearing loss in a population of deaf children with special reference to genetic factors. J. Laryngol. Otol. 89 No. 9.
International Journal of Pediatric Otorhinolaryngology
ELSEVIER
34 (1996)
75-85
Hearing impairment among ‘at risk’ children Hamad S. Al-Muhaimeed* Drpartmrnt of Otorhinolaryn~ology, King Abdul Azi: Urtitxrsit~* Hospital. P.O. Box 24.5,Riyudlr 1141. Saudi Arubiu Received 18 October
1994: revision received 9 June 1995; accepted 12 June 1995
Abstract A survey was carried out to identify the prevalence and the aetiology of hearing impairment among infants and children at risk based on the criteria. Out of 6421 surveyed children, 1256 (19.6%) were found ‘at risk’ for hearing impairment. Children with hearing impairment in this study were found to be 494 which represent 39.3% of the ‘at risk’ children. We found 326 (66%) children had conductive hearing loss almost all associated with secretory otitis media (n = 232). Sensorineural hearing loss affected 168 (34%) children. Heredo-familial causes were responsible for about 111 (66.1%) cases. The detailed causes of conductive and sensorineural hearing loss are presented and compared with other studies in the literature. Conductive hearing impairment was mild in the majority of the cases n = 27 1, (83X), moderate in 55 (17%) cases. Sensorineural hearing loss was mild in 113 (67,3X), moderate in 32 (19%) and profound in 23 (13.7%) cases. A large scale Kingdom-wide study to focus on aetiology of deafness among Saudi infants and children to find out the extent of this problem is recommended. Keywords: Sensorineural hearing loss; ‘At risk’ child; Consanguinity
1. Introduction Hearing is necessary to learn language and speech and the development of the baby is highly dependent upon hearing, and the social, emotional and intellectual
development is bound up with the normal functioning of the auditory system. Ewing and Ewing (1950) [7] have described in detail the effect of a hearing disability * Corresponding author Ol65-5876/96/$09.50 0 1996 Elsevier Science Ireland Ltd. All rights reserved SSDI 0165-5876(95)01254-Z
16
H.S. AI-Muhaimeed
/ Int. J. Pediatr. Otorhinolaryngol.
34 (1996) 75-85
on a developing child, as well as the importance of hearing on physical attributes of breathing, a sense of rhythm, walking, eating, drinking and personal habits. Hearing impairment during infancy and childhood has its greatest effect on language development and even a mild loss can interfere with the natural growth. Therefore, early detection and intervention will minimize the effect of such disability. In order to guarantee the earliest possible identification of hearing impairment, hearing screening of all the neonates has been advocated [4]. However, the results of mass screening programs were found to be inconsistent, misleading and unnecessarily expensive [3]. The Joint Committee of Infant Hearing and Screening (1982) [lo] recommended that infants at high risk for hearing impairment should be identified by means of history and physical examination. The Infant High Risk Register lists the following factors: 1. A family history of hearing impairment; 2. Congenital perinatal infection; 3. Anatomic malformations of the head and neck; 4. Low birth weight ( < 1500 g); 5. Hyperbilirubinemia; 6. Bacterial meningitis; 7. Severe neonatal asphyxia. After identifying the high risk infants and children, they are subjected to screening tests. Those children who fail the screening tests are then referred for full diagnostic tests which vary according to the age, co-operation, mental condition facilities available, etc. Using the above criteria, this study aims at identifying the aetiological factors of hearing impairment in high risk infants and children using full diagnostic hearing evaluation including appropriate laboratory investigations. This is the first study of its type in Saudi Arabia on the epidemiology and possible aetiology of deafness. 2. Materials
and methods
A comprehensive survey of 6421 Saudi infants, pre-school and school-age children from 2 months up to 12 years was carried out in Riyadh in the period between May 1988 and September 1990. The sampling design was essentially based on quota sampling using two interlocked quota controls, age and sex. On the other hand, in order to have an adequate and representative coverage of all socio-economic and demographic groups of the residents of Riyadh, it was necessary to introduce an element of randomness during the actual sample selection process. Therefore, a stratified three-stage random sampling frame of Riyadh administrative areas and roads was established as follows: A field work was carried out to enumerate and number the administrative areas and roads of Riyadh. This field work included the outlining of administrative areas and dividing them into roads. It was decided to use the method of areas and roads
H.S.
AI-Muhaimeed
I ht.
J. Prdiatr.
Ororl~it~oIr~r~~r~~ol. 34 (IYY6)
75-85
17
for sample withdrawing to facilitate data collection. It was decided not to use methods of sampling by aerial maps, though in theory, it is an excellent method. However, for the city of Riyadh, there would have been some difficulty in identifying segments inside each area by using a grid map because the segments are not numbered and there are no names for the land marks which would have helped in outlining boundaries of the segments. Road locations were adopted because this was easier each road has a number and there were marks which indicated the road limits on both sides. The sample withdrawing could be summarized as follows: 1. Riyadh was divided into 93 administrative areas (Table 1). They were further divided into six strata according to socio-economic homogeneity; 2. In each stratum the number of areas were identified and one fifth of the areas in each stratum were chosen randomly to be included in the study as presented in Table 1; 3. Each randomly selected area was further subdivided into roads, altogether, there were 1376 roads in the 17 randomly selected areas. One-sixth of the roads in each of the 17 areas selected for the first stage of the study was chosen randomly. Two-hundred-and-twenty-four roads were randomly selected for the study; 4. Each road was subsequently divided into smaller manageable blocks of approximately equal size and samples of such blocks were randomly selected. 2.1. Field survey design und procedures jbr dmt collection Within each block selected, a random starting point was chosen and each survey team was asked to follow a pre-determined zigzag route calling at every other household encountered. There were two survey teams. Each survey team included an E.N.T. specialist, a nurse, a social worker, a field supervisor and a driver. The teams established whether there were any children in the household. If so, and after obtaining permission from the family. the team proceeded to the clinical examination of the child and completed the relevant questionnaire with the mother. In order to meet the required quotas, daily records of contacts were submitted to the field supervisors who were responsible for co-ordinating the field operations. Table I Total number of administrative areas of Riyadh and areas surveyed according respect to socio-economic status
to homogeneity
with
Stratification according to homogeneity with respect to socio-economic status
Total # of areas in each socio-economic stratum
No. of areas sampled for the survey (I 5 of areas from the total number of areas in each socio-economic stratum)
Stratum Stratum Stratum Stratum Stratum Stratum
Only Only Only Only Only Only
Only Only Only Only Only Only
Total
I 2 3 4 5 6
93
6 areas I2 areas I6 areas I5 areas 7 areas 37 areas
I7
I 2 3 3 I 7
area areas areas areas area
areas
78
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A number of interviews, anthropometric measurements and clinical examinations were also carried out in the Well-Baby Clinics and Maternal-Child Health Centers which had been previously randomly selected. This sampling procedure, had four major advantages: 1. Randomness of the study sample; 2. Control over the sample size in each age group in order not to exceed the required number in each age and sex group, or fail to reach the required number. Since there is a predominance of children below the age of 6 years, we decided the proportion of children < 6 years not to exceed 2:l to those over 6 years; 3. Manageability of the implementation of the task in terms of time and resources allocated for the completion of each age group in the survey; 4. Precise estimation of children’s age and other related data. 2.2. Study procedure
In various city blocks, individuals who were ‘at risk’ for hearing impairment were determined by the presence of one or more of the following: 1. History of genetically-determined childhood hearing impairment; 2a. Identification of the etiological agents of congenital infection: TORCH agents (e.g. toxoplasma, syphilis, rubella cytomegalovirus, herpes); 2b. Identification of the aetiological agent of chronic otitis media or secretory otitis media which may attribute to hearing impairment; 3. Rubella or other non-bacterial intrauterine foetal infection (e.g. cytomegalovirus and herpes infection); 4. Defects of the ear, nose or throat. Malformed, low set or absent pinnae, cleft lip or palate (including submucous cleft); any residual abnormality of the otorhinolaryngeal system; 5. Prematurities or birth weight < 1500 grams; 6. Cyanosis; 7. High bilirubin concentrations that exceed the level necessaryfor blood transfusion. The first draft of the research protocol was tested during an initial 3 month pilot phase and was further modified according to the analysis of pilot data and assessment of the epidemiological and statistical co-ordinators of the research program. 2.3. Data processing and analysis
All completed research protocols were submitted to the project methodological unit each day and were edited on a daily basis to ensure that possible errors could be immediately identified and corrected. The data was then processed by a computer using statistically package for biomedical sciences(BMDP) every 6 months. All the infants and children who participated in the study were exposed to full ORL clinical examination after taking a detailed history from their parents including social and family history. Hearing of children below 6 years were evaluated by brain stem evoked response (Type Amplaid MK15) and older children were
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Table 2 Age and sex distribution of ‘at risk’ children Age group
Number
Male
Female
I6 years 6612 years
831 (66.2%) 425 (33.8%)
514 (61.9%) 276 (65%)
317 (38.1%) 149 (35%)
Total
1256 (100%)
790 (63.0%)
466 (37.0%)
evaluated by pure tone audiometry (Type GSI 10) Tympanometry was done on all children. Tympanometry does not evaluate hearing levels, but may give information on the topical site of a hearing lesion. Appropriate blood specimens were collected and sent to the laboratory to allow identification of the aetiological microbiological agents. The assay performed included IgG, IgM antibodies to TORCH agents which were tested for by an enzyme immunoassay using Virgo, ELISA reagents and automated Virgo equipments Model 400AT. The tests were carried out according to the instructions of the manufacturers. Appropriate positive and negative controls were used. Positive IgM antibodies specific to any of TORCH agents or a fourfold rise in specific IgG antibody titre were considered a potential aetiological agent for hearing impairment. 3. Results
Out of a total of 6421 infants and children 1256 (19.56%) were identified as ‘at risk’ for hearing impairment. Table 2 shows the distribution by age and sex of the ‘at risk’ children. About two third (63%) were males and a third (37%) were females. Two-thirds (66.2%) of the participants were 6 years and below whereas the remaining were older than 6 years. The number of children with hearing impairment were found to be 494 which represent 39.3% of the ‘at risk’ children (Table 3). Three-hundred-and-twenty-six children were suffering from different degrees of conductive hearing loss (Table 3) which forms 26% of the ‘at risk’ group. Most of the casesof conductive loss (232) were due to secretory otitis media (Table 4). Table 3 Types of deafness among ‘at risk’ children Number Bilateral sensorineural hearing loss Unilateral sensorineural hearing loss Familial progressive sensorineural hearing loss Mixed hearing impairment Conductive hearing impairment Undetermined
61 13 26 54 326 8
Total
494
Percent of the risk group 5.3 1.0 2.1 4.3 26 0.6 1256
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Table 4 Causes of hearing impairment Causes
Number
1. Secretory otitis media 2. Suppurative otitis media 3. Heredo-familial and consanguinity 4. Mumps 5. Meningitis 6. Rubella 7. Low birth weight 8. Down’s syndrome 9. Unknown (sensorineural hearing loss)
232 94 III 4 I5 4 17 2 15
Total
494
Percentage 47.0 19.0 22.5 0.8 3.0 0.8 3.4 0.4 3.0 100
One-hundred-and-sixty-eight had sensorineural hearing loss which represent 34% of all children with hearing loss. The different causes of hearing loss are given in Table 4. Secretory otitis media is the commonest cause of conductive hearing loss affecting 47% of children with hearing impairment. This is followed by suppurative otitis media (19%). On the other hand, the commonest cause of sensorineural is heredo-familial causes affecting 111 (22.5%) children and infants and this represents 66.1% of all cases of sensorineural deafness. Other causes were due to prematurity (3.4%) meningitis (3.0%) rubella (0.8%) mumps (0.8%) and Down’s syndrome (0.4%). Fifteen cases (3.0%) were classified as of unknown causes. Conductive hearing loss was mild in the majority of the cases, n = 271 (83%) moderate in 55 (17%) cases (Fig. 1). Sensory neural hearing loss was mild in 113 (67.3%) moderate in 32 (19%) and profound in 23 (13.7%) cases(Fig. 2). 4. Discussion
The number of children considered to be ‘at risk’ of hearing impairment were found to be 1256, about one fifth of all the surveyed children (6421). It is known that the details of ‘at risk’ registers vary from place to place with consequent variation in efficiency in detecting deafness and to be effective, an ‘at risk’ register must have a prevalence rate of 14 times greater than the general population [16]. The number of children with hearing impairment in this study were found to be 494 (39.3%) of the ‘at risk’ children. The very high prevalence of deafness(39.3%) among the at risk group is striking. This could be due to the efficiency of detecting the minor degreesof conductive and sensory neural hearing loss using objective diagnostic tests; but further investigation is needed to reach firm conclusions about the efficiency of our criteria of the ‘at risk’ register. The number of casesof conductive hearing impairment was 326 (26%) (Table 3) of all surveyed children and the majority (n = 232) were due to secretory otitis
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media (Fig. 1). The epidemiology of such disease is poorly documented and shows wide variation according to the geographical location, age and methods of identification. The prevalence of middle ear effusion varies from 8.7% (reported by Suarez Nieto et al., 1983) [17] among Spanish children aged from 2 months to 12 years; to 50% prevalence reported by Brooks (1976) [5] in children aged 557 years in the UK. Our study’s relatively low prevalence of 18.5% may be due to the age distribution of the sample, the seasonal variation or actual low prevalence of such a disease. Suarez Nieto et al. (1983) found the prevalence of secretory otitis media decreased with increasing age from 38.8% at 2 years to 1.1% at 11 years. The number of sensorineural hearing loss caseswas 168 (13.4%) of all surveyed children (Fig. 2). This figure is higher than the prevalence of 1.1- 1.7% reported by others [8,9] and reflects the importance of sensory neural hearing impairment as a major health problem in Saudi Arabia in comparison with other parts of the world. When analysing the different underlying causes of sensorineural deafness, hereditary hearing impairment was found to be the most common single cause, being established in 111 cases, which represent 66.1% of all cases of sensorineural deafness. Again, this represent a significantly higher prevalence than other reports approximately one half of sensorineural hearing loss in children was attributed to hereditary causes [14,15]. Also, the prevalence of hereditary deafness (1.7% of the total number) is markedly higher than the prevalence of 1 in 2000 to 1 in 6000 live birth given by other authors. This high prevalence of hereditary deafness may be explained, in part, by the widely practiced consanguinity in Riyadh. The high prevalence of consanguinity in Saudi Arabia is evident from this study. First cousins was found in 22.1% of the parents and more distant consanguinity was present in another 23% (Table 5). It is estimated that 75.9% of hereditary hearing loss is caused by single gene recessiveautosomal transmission [lo]. Consanguineous marriage increases the chance that the two parents may each have the same recessive gene inherited from their common ancestor and this increases the
oderate
conductive
Mild conductive hearing ,109~ n = 271 Fig. 1. Hearing severity of children with conductive
hearing loss (n = 326).
82
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34 (1996) 75-85
SNHL
Profound
SNHL
Mild SNHL n 113 q
Fig. 2. Hearing severity of children with sensorineural
hearing loss (n = 168).
proportion of homozygotes, at the expense of heterozygotes. On the other hand a consanguineous marriage also increases the risk of transmission of polygenic (multifactorial) inheritance which may play a minor role on the transmission of some casesof hereditary deafness. The efficiency of detecting genetic deafness may play a part in the increase in cases of hereditary deafness in some earlier studies, including the current survey. Taylor et al. (1975) [18] reported that most, if not all, casesof deafness previously classified as of ‘unknown cause’ are casesof autosomal recessive inheritance. The hereditary deafness may appear at the time of birth or may be delayed developing after birth. The diagnosis of hereditary deafnessis usually based on careful study of the family, pregnancy, birth and infancy history and by careful physical examination of the affected individual and other family members in addition to the necessary laboratory work. Low birth weight was found to be the second commonest cause of sensorineural hearing loss among the children in the current study. Children born with low birth weight accounted for 10.2% (n = 128) of the participants. Seventeen children of those were found to have sensorineural hearing loss primarily caused by the low birth weight itself (after excluding children exposed to other aetiological factor of Table 5 Consanguinity Parent’s relation First cousins Relatives Not relatives Total
of parent (n = 1256) Percent 21.1 23.0 55.9 100.0
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deafness). These data mean that 13.3% of the low birth weight children suffered from deafness directly attributed to the low birth weight and also mean that low birth weight accounted for 10.1% of the childhood sensorineural deafness. This relatively low frequency in our study is probably due to the exclusion of low birth weight children who have been exposed to other causative factors of childhood deafness, particularly asphyxia and jaundice. It is worth noting that deafness among low birth weight infants has been attributed to several factors, such as the ‘immaturity’ the use of ototoxic drugs, the ambient noise of the incubators in which these infants were nursed and the presence of some perinatal complications (e.g. hypoxia, acidosis) that are likely to produce brain damage and which are more frequently encountered among low-birth-weight infants [ 1,2]. Meningitis as a cause of a sensorineural deafness was shown in 15 cases (8.9%) of the 168 children with sensorineural hearing loss. Several studies of school age children in different parts of the world have shown that bacterial meningitis is the cause of 8-24% of all cases of severe deafness [12]. Post-meningitis sensorineural hearing loss may be unilateral or bilateral and may be partial or complete. The incidence of partial hearing loss in the literature ranges between 20 and 70% [12]. Post-meningitis deafness is unilateral in 20-60% of cases [11,13]. Since no specific therapy can be recommended to diminish the incidence of sensorineural deafness following meningitis, prevention of meningitis is the only means to reduce such a serious complication. Vaccination against the three most common causes of bacterial meningitis are now available and their use should be encouraged. Four cases (2.4%) of the sensorineural deafness are attributed to maternal rubella. This relatively low incidence is in contrast to the findings of Martin (1982) [l l] who found rubella to be the commonest identifiable cause of congenital sensorineural deafness (25%) in children of the European Community. In contrast to the common belief, rubella at any stage in the pregnancy can cause deafness. Nowadays the laboratory diagnosis of congenital rubella may be established by: the isolation of rubella virus from urine or throat cultures during the first week of life: the identification of IgM antibodies against rubella in serum from the neonate; and an increasing antibody titre to rubella virus in an infant during the first few months of life [6]. The sensorineural hearing loss encountered in these cases is usually severe to profound. Screening and vaccination programmes have markedly reduced the incidence of congenital deafness due to rubella. Mumps accounted for four cases (2.4%) of sensory neural hearing loss. Hearing loss associated with mumps occurs in about 5 of every 10 000. Deafness is usually unilateral and profound. Mumps is probably the most common cause of unilateral acquired sensorineural hearing loss in children [l4]. The number of children with sensorineural hearing impairment classified as of unknown cause was 15, representing 8.9% of all cases with hearing impairment. In many earlier reports approximately 30-35% of the cases are placed in a category of ‘unknown cause’ [ll]. Many authors believe that most cases of deafness of undetermined causes are cases of autosomal recessive inheritance [g]. A follow-up of those children may reveal additional pertinent information which may be instrumental in determining the cause of deafness. Feinmesser et al., 1986 [g]
84
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followed 44 deaf children of unknown cause (representing 41.4% of 107 deaf children) and were able to determine the cause of deafnessin 12 of them. Therefore, the percentage of the group with unknown aetiology dropped from 41.4 to 28% in their series. 5. Recommendations 1. To carry out a large scale Kingdom wide study to find out what is the extent of this problem in the Kingdom of Saudi Arabia. 2. AS this study has indicated that consanguineous marriage is prevalent in the Kingdom, a comprehensive genetic study should also be carried out in order to find out the heredo-familial aetiology of deafness and its magnitude. 3. Since early diagnosis is essential for the successful treatment and the proper development of speech, all babies should undergo screening tests for hearing around the age of 6 months. This is in view of the fact that there is no existing policy to such screening. In the management of the children with hearing impairment it is crucial to take into consideration that the ability to learn auditory discrimination diminishes, as the child grows older. In this respect it is important to appreciate that the first year of life is the most crucial time for having normal hearing. Accordingly, the child with hearing impairment should be taught to hear as early as possible. As far as hearing aid is concerned, it should be fitted at the earliest ages; this often being at ages as young as 10 months when the child will accept it and does not pull it out. 4. Since total deafness is quite rare and only l-2% of deaf children have no hearing at all, all children with hearing impairment should have a 2 year auditory training before being regarded as totally deaf. Family guidance should start from the day hearing impairment is diagnosed, being undertaken by an audiologist and by the specialist teacher of the deaf. The teacher should train the mother of the hearing impaired child on how to handle her child so as to bring sound to him or her. 5. Hearing impairment is a preventable ailment especially when it is due to inflammatory causes such as otitis media. In the current study 66% of the children with hearing impairment had otitis media making it the major cause. Furthermore, 22.5% of the hearing impairment in this study were due to hereditary causes mainly due to consanguineous marriage. Therefore, early detection of infection and family counselling could be most effective in preventing hearing impairment in Saudi Arabia. Acknowledgement I would like to thank King Abdul Aziz City for Science and Technology (KACST) for sponsoring this study; Prof. Siraj M. Zakzouk for his great support and Ms. Connie Unisa for her secretarial work.
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