Childhood deafness in southern Africa. An aetiological survey of 3,064 deaf children

Profile of childhood hearing loss in the Western Cape, South Africa

OBJECTIVES

To describe the nature, associated risk factors and age of diagnosis for childhood hearing loss in a South African cohort from the Western Cape Province.

METHODS

A retrospective review of clinical data from children under six years of age with confirmed hearing loss at Red Cross War Memorial Children's Hospital (RCWMCH) was conducted between 1 January 2019 and 31 July 2019. Data collected included demographic information, type and degree of hearing loss, documented risk factors associated with hearing loss, and age of suspicion and diagnosis of hearing loss.

RESULTS

The study sample included 240 children with hearing loss, with a mean age of 42 months (21.8 SD; range 2-72). More than two thirds (68.3%) of the children presented with bilateral hearing loss. The majority presented with conductive hearing loss (64.6%), followed by sensorineural (28.7%) and mixed hearing loss (3.3%) or auditory neuropathy spectrum disorder (3.3%). More than half (51.8%) of the bilateral sensorineural hearing losses were of a profound degree. The most prominent risk factor for conductive hearing loss was otitis media, for sensorineural hearing loss it was a family history of childhood hearing loss, and for auditory neuropathy spectrum disorder it was hyperbilirubinaemia. Approximately one third of patients (27.1%) with sensorineural hearing loss did not have any associated risk factors. The mean age of diagnosis of permanent congenital or early-onset hearing loss was 31.4 months (22.8 SD; range 2-72), with a mean delay of nine months (13.2 SD; range 0-60) between age of suspicion and diagnosis of hearing loss (n = 93).

CONCLUSIONS

The large proportion of preventable hearing losses in this sample highlights the importance of maximising primary health care efforts to treat preventable causes timeously. Age of diagnosis of permanent congenital or early-onset hearing loss was severely delayed undermining prospects of positive outcomes through early intervention. Infant hearing screening services in the public health sector of South Africa should be prioritised alongside primary health care efforts to reduce preventable risks for hearing loss.

High Risk Factors Associated With Early Childhood Hearing Loss: A 3-Year Review

PURPOSE

In this study, we examined the association between risk factors for hearing loss and early childhood hearing status (normal hearing, congenital hearing loss, or delayed-onset hearing loss). Follow-up rates of audiologic care following passed or referred birth screens for children with risk factors were also examined.

METHOD

A retrospective data review was completed on 115,039 children born from 2010 to 2012. Data analyses included prevalence rates, odds ratios, and Fisher exact tests of statistical significance.

RESULTS

Ninety percent of children were born with no risk factors for hearing loss; of those, 99.9% demonstrated normal hearing by 3 years of age. Of the 10% of children born with risk factors, 96.3% demonstrated normal hearing by age 3, 1.4% presented with congenital hearing loss, and 2.3% demonstrated permanent hearing loss by age 3. Factors that placed children at the highest risk of congenital hearing impairment were neurodegenerative disorders, syndromes, and congenital infections. Factors that placed children at the highest risk of developing permanent postnatal hearing loss were congenital cytomegalovirus, syndromes, and craniofacial anomalies.

CONCLUSIONS

Certain risk factors place a child at significantly greater risk of congenital hearing impairment or developing permanent hearing loss by age 3. Follow-up diagnostic testing should remain a priority for children with certain risk factors for hearing loss.

Profound childhood hearing loss in a South Africa cohort: risk profile, diagnosis and age of intervention

OBJECTIVE

To describe profound childhood hearing loss in a South African population of pediatric cochlear implant recipients in terms of risk profile, and age of diagnosis and intervention.

METHODS

A retrospective review of patient files for 264 pediatric cochlear implant recipients from five cochlear implant programs was conducted. Data was captured from 264 eligible subjects, of which all were implanted between 1996 and 2013 and PCEHL was confirmed under the age of 5 years old. Data collected included demographical information, risk factors from case histories, diagnostic test procedures conducted, diagnosis (type, onset and degree of hearing loss) and documented ages of caregiver suspicion, initial diagnosis and intervention.

RESULTS

Risk factors for permanent childhood hearing loss were present in 51.1% of cases, with the most prevalent risks being NICU admittance (28.1%), family history of childhood hearing loss (19.6%) and prematurity (15.1%). An associated syndrome was diagnosed in 10% of children and 23.5% presented with at least one additional developmental condition. Hearing loss for most (77.6%) children was confirmed as congenital/early onset, while 20.3% presented with postnatal onset of hearing loss. ANSD was diagnosed in 5% of children, with admittance to NICU (80%) and hyperbilirubinemia (50%) being the most prevalent risk factors for these cases. Hearing loss was typically diagnosed late (15.3 months), resulting in delayed initial hearing aid fitting (18.8 months), enrollment in early intervention services (19.5 months) and eventual cochlear implantation (43.6 months).

CONCLUSION

Most prevalent risk factors in profound childhood hearing loss were admittance to NICU, family history and prematurity. Diagnosis and intervention was typically delayed predisposing this population to poorer outcomes.

Childhood hearing loss and risk profile in a South African population

OBJECTIVE

To describe the nature of hearing loss and associated risk profile in a South African population of infants and children diagnosed at a pediatric referral clinic.

METHODS

A retrospective review of patient files for a pediatric auditory evoked potential clinic in Pretoria was conducted (January 2007-December 2011). Collected data included demographical information, risk factors from case history questionnaire, diagnosis (type and degree of hearing loss), documented age of caregiver suspicion and age of first diagnosis.

RESULTS

Hearing loss was present in 73% (73/100) of cases evaluated. Permanent hearing losses (SNHL, ANSD and mixed) constituted 76% of losses. Unilateral hearing losses constituted 8% of SNHL and 20% of conductive hearing loss. ANSD was diagnosed in 21.4% and SNHL in 78.6% of permanent non-conductive hearing loss cases. The most prevalent SNHL risk was family history of hearing loss and for ANSD it was admittance to the NICU for more than 5 days. The majority of the sample was diagnosed with a permanent bilateral SNHL and ANSD after 36 months of age (47%) despite 40% already suspected of having a hearing loss before 12 months of age.

CONCLUSIONS

A high prevalence of ANSD was found with preventable risk factors often indicated. Age of diagnosis was significantly delayed, evidencing the lack of early hearing detection services in South Africa. The majority of children were diagnosed at ages precluding optimal benefits from early detection and subsequent intervention.

Neonatal hearing screening and intervention in resource-limited settings: an overview

From a developmental perspective, optimal speech and language outcome is indisputably the primary motivation for neonatal hearing screening of infants with congenital or early-onset hearing loss (PCHL). This paper additionally outlines more broadly the potential value of early hearing detection and intervention in resource-poor countries against the backdrop of limitations of primary prevention of PCHL based on a review of literature from low-income and middle-income countries with per capita incomes of approximately US$6000 or less. It establishes the scientific and developmental foundation for priority consideration for neonatal hearing screening and intervention in any global initiatives for effective early childhood development programmes in resource-limited countries. It also highlights approaches to addressing the various challenges to implementing effective early hearing detection and intervention programmes, and concludes with a discussion on the pivotal role of paediatricians in facilitating timely referral for requisite tests and (re)habilitative services especially for infants with established risk factors.

Community-based infant hearing screening for early detection of permanent hearing loss in Lagos, Nigeria: a cross-sectional study

OBJECTIVE

To determine the feasibility and effectiveness of a community-based universal infant hearing screening programme for detecting permanent congenital and early-onset hearing loss (PCEHL) in Lagos, Nigeria.

METHODS

This is a cross-sectional study in which all infants aged 3 months or under attending four bacille Calmette-Guérin (BCG) immunization clinics accounting for over 75% of the BCG coverage in the study location were screened by community health workers between July 2005 and April 2006. Screening followed a two-stage protocol involving transient evoked otoacoustic emissions and automated auditory brainstem responses. The main outcome measures were screening coverage, referral rates, return rates for second-stage screening and evaluation, yield and age at PCEHL diagnosis.

FINDINGS

In total, 2003 (88%) of 2277 eligible infants attending the four BCG clinics were successfully screened between July 2005 and April 2006 at a mean age of 17.7 days, with no parent declining screening. The majority (55.2%) were born outside a hospital and, of such infants, 77% were born in traditional herbal maternity homes. The overall referral rate for diagnostic evaluation was 4.1%. Only 61% (50/82) of those referred returned for evaluation, and 45 of them were confirmed with PCEHL. Additionally, 11 infants who had previously passed the first screening stage were also found to have PCEHL, resulting in a yield of 28 per 1000 (56/2003). The mean age at diagnosis was 51 days. The sensitivity, specificity and positive predictive value of the first screening stage were 80.4%, 99.7% and 90.0%, respectively. The positive likelihood ratio was 268, while the negative likelihood ratio was 0.2.

CONCLUSION

Routine hearing screening of infants attending BCG immunization clinics by community health workers was feasible and effective for the early detection of PCEHL in Lagos, Nigeria. However, an efficient tracking and follow-up system is needed to improve return rates for second-stage screening and diagnostic evaluation.

Syndromic etiology in children at schools for the deaf in Turkey

OBJECTIVE

The aim of this study was to determine the syndromic etiology of bilateral severe sensorineural hearing disorders in children and current etiological causes to reduce the cases in the unknown group.

METHODS

This study was conducted on 550 students of five schools for the deaf in Istanbul and Zonguldak, Turkey. Otologic, audiologic, dysmorphologic, ophthalmologic and dental examinations were performed in all children. Familial and medical histories were obtained.

RESULTS

The etiology of hearing loss was genetic in 346 (62.90%), acquired in 107 (19.45%) and unknown in 97 (%17.63) cases. A total of 619 malformations were defined in 550 children and 99 of them belonged to a syndrome. We identified 33 different syndromes for these 99 syndromic children. Syndromic etiology was found in 18.0% of the total and 28.61% of the subjects with genetic etiology. Most common syndrome was Waardenburg syndrome which occurred in 33 children.

CONCLUSION

The incidence of hereditary hearing impairment is very high in developing countries compared to developed countries. Prevention is essential to reduce the incidence, multidisciplinary approach and genetic counselling are necessary in this regard.

Benefits and challenges of newborn hearing screening for developing countries

The late detection of permanent congenital and early-onset hearing loss (PCEHL) often has severe effects on linguistic, speech, cognitive and educational development in affected children. Since newborn hearing screening (NHS) allows most PCEHL to be detected early enough for optimal intervention, the prospects of its introduction in the developing world are reviewed in this paper. It is observed that a simple generalisation on the feasibility of NHS for the developing countries seems inappropriate in view of the diversities in the health and socio-economic status of these countries and the recent favourable reports of universal newborn hearing screening from the region. NHS empowers parents to make timely choices that will allow their hearing impaired children to be given a good start in life and be fully integrated into the wider community. It also compels attention towards the development of essential hearing healthcare services, besides the specific documented benefits. Existing child-healthcare structures such as the expanded programme on immunisation (EPI), baby friendly hospital initiatives (BFHI) and integrated management of childhood illness (IMCI) provide opportunities for the introduction of some form of NHS in many of these countries where routine or systematic childhood hearing screening does not exist. Limited funding, manpower shortages, inadequate support services, low public awareness and the uncertainty regarding the commitment from healthcare practitioners may present some challenges but these are not insurmountable. Pilot studies are necessary in each country to provide empirical data that will guide healthcare providers who wish to introduce such a programme at any level of healthcare delivery.

Piebaldism with deafness: molecular evidence for an expanded syndrome

In a South African girl of Xhosa stock with severe piebaldism and profound congenital sensorineural deafness we identified a novel missense substitution at a highly conserved residue in the intracellular kinase domain of the KIT proto-oncogene, R796G. Though auditory anomalies have been observed in mice with dominant white spotting (W) due to KIT mutations, deafness is not typical in human piebaldism. Thus, the occurrence of sensorineural deafness in this patient extends considerably the phenotypic range of piebaldism due to KIT gene mutation in humans and tightens the clinical similarity between piebaldism and the various forms of Waardenburg syndrome.

Familial streptomycin ototoxicity in a South African family: a mitochondrial disorder

The vestibular and ototoxic effects of the aminoglycoside antibiotics (streptomycin, gentamycin, kanamycin, tobramycin, neomycin) are well known; streptomycin, in particular, has been found to cause irreversible, profound, high frequency sensorineural deafness in hypersensitive persons. Aminoglycoside ototoxicity occurs both sporadically and within families and has been associated with a mitochondrial DNA (mtDNA) 1555A to G point mutation in the 12S ribosomal RNA gene. We report on the molecular analysis of a South African family with streptomycin induced sensorineural deafness in which we have found transmission of this same predisposing mutation. It is now possible to identify people who are at risk of hearing loss if treated with aminoglycosides in the future and to counsel them accordingly. In view of the fact that aminoglycoside antibiotics remain in widespread use for the treatment of infections, in particular for tuberculosis, which is currently of epidemic proportions in South Africa, this finding has important implications for the family concerned. In addition, other South African families may potentially be at risk if they carry the same mutation.

Childhood hearing loss in sub-Saharan Africa: a review and recommendations

Nearly 10% of the world's population lives in sub-Saharan Africa, a region comprised of many countries with least developed nation status. The region has a predominantly young population and many children in the region are at risk of pathologies associated with hearing loss. Despite the constraints associated with low socioeconomic levels, a number of valuable studies have been carried out into the prevalence and etiology of childhood hearing loss in the sub-Saharan region. A review of the published literature related to childhood hearing loss in sub-Saharan Africa is presented and recommendations made on possible future research directions that could assist hearing loss prevention and management.

The sex-ratio in childhood deafness, an analysis of the male predominance

The sex-ratio in childhood deafness is analyzed and shows an unexplained male predominance. A review of the literature is presented and to this is added the sex-ratio of 3278 ex-pupils from the Dutch Institute for the Deaf in St. Michielsgestel. Also the sex-difference of 162 deaf children is presented and related to the degree of hearing loss and the etiology of their deafness. The population of these hearing impaired and deaf people consists of an average of 54% men and 46% women. Although hereditary etiology was spread equally over both sexes of the 162 pupils in the Nijmegen school, a significant difference for the autosomal dominant forms of hearing impairment have been observed. An explanation for this male predominance is still lacking.

Causes of childhood deafness at a Dutch school for the hearing impaired

This study was conducted on 162 hearing-impaired school pupils who were investigated as to the cause of their hearing loss. In 64 pupils (40%) a hereditary cause was recognized, and in 43 (27%), an acquired cause; in 55 (34%) the cause remained unknown, according to the criteria we used for defining a cause. Special attention was paid to the differences between the hereditary and acquired forms of deafness in relation to the degree of hearing loss. The study population therefore was divided into groups per 10 dB of hearing loss. Using this method we found that an autosomal dominant hearing loss occurred significantly more frequently among the less severe hearing disorders. This finding, which has not been seen in the literature, is important in genetic counseling for the deaf. Another remarkable finding was that Usher's syndrome, especially type 2 with a moderate hearing loss, was more frequent among the hearing-impaired subjects than we had expected.

Hearing impairment and pigmentary disturbance

Hearing impairment is a variable manifestation of several heritable conditions in which pigmentation of the skin or eyes is abnormal. Some of these disorders are well recognized although uncommon, while others are virtually private syndromes. Practical issues concerning the major conditions of this type are reviewed in this article on a basis of a survey of 4452 profoundly deaf children attending special schools in Southern Africa, together with investigations in affected families. The Waardenburg syndrome (WS), which is the most common deafness-depigmentation disorder, was present in 121 (2.7%) of the 4452 deaf scholars. Further studies in 7 multigeneration affected families confirmed phenotypic variability and indicated a need for internationally agreed diagnostic criteria. In 4 Cape Town families of mixed ancestry the WS-I gene was linked to the 2q37 locus, but in another large kindred no linkage could be demonstrated. Nonallelic heterogeneity is possible. There is uncertainty concerning possible interrelationship between WS and piebaldism. The phenotypic consistency of a South African family in which 7 persons in 3 generations had gross piebaldism in the absence of disturbance of hearing or involvement of the eyes and periorbital structures is suggestive that this disorder and WS are separate entities. Molecular investigations indicate that the gene for piebaldism in this kindred is not situated at the WS-I locus 2q37. Deafness and hyperpigmentation are present in neurofibromatosis type II (acoustic neuromata) and the multiple lentigines syndrome, while retinal pigmentation is a feature of the Usher syndrome. This latter entity is apparently much less common in Southern Africa than in other parts of the world.

A study of deafness in West Africa: the Gambian Hearing Health Project

Research was carried out on various aspects of deafness in a West African population. A national survey of childhood deafness was completed to discover the incidence and causes of severe to profound hearing loss in The Republic of the Gambia. A large school screening campaign was conducted to determine the prevalence of middle ear disease in Gambian children. Smaller studies concerned the hearing loss among post-meningitis patients; the disease pattern of audiology clinic patients in both urban and rural areas; the degree of hearing loss associated with otitis media and the rubella serology of a group of Gambian women and children. It was found that meningitis was a major identifiable disease causing deafness. Rubella and measles, often causes of deafness in other tropical countries, did not seem to be of such importance in The Gambia. Familial factors also accounted for little of the childhood deafness as far as it was possible to tell. Chronic middle ear infections could give rise to considerable hearing loss but rarely led to the dangerous complications often seen in other tropical communities. Effective medical and audiological services for the deaf are difficult to implement in developing countries. A primarily preventive approach may prove to be the most rational way of helping the deaf in The Gambia.

Autosomal dominant inheritance of conductive deafness due to stapedial anomalies, external ear malformations and congenital facial palsy

Three siblings of Indian stock had profound bilateral conductive deafness with variable malformations of the external ears, stapedial abnormalities and facial paralysis. Their mother was similarly affected and inheritance of this private syndrome is evidently autosomal dominant. Some improvement of auditory function was obtained by surgical intervention in the middle ear.