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Globally, approximately 0.5 to 5 in every 1 000 neonates and infants present with congenital or early childhood onset hearing impairment that is severe to profound (WHO, 2010). More recent estimates indicate that 34 million of the 466 million individuals worldwide with disabling hearing loss are children, of whom 7.5 million are below five years of age (Neumann, Chadha, Tavartkiladze, Bu, & White, 2019). Within this global framework, prevalence rates have been reported to be higher in low and middle-income (LAMI) contexts, which are worst affected (Olusanya & Newton, 2007). These countries comprise 80 percent of the worlds' population, and are home to two-thirds of individuals with hearing impairment (Tucci, Merson, & Wilson, 2010). A review of population-based studies in 2011 estimated that 16 million children have a hearing impairment ≥35 decibel hearing level (Stevens et al., 2011). From this global estimate, prevalence rates were noted as being the highest in South Asia, sub-Saharan Africa and the Asia Pacific regions (Neumann et al., 2019; Stevens et al., 2011). Although these results are not specific to newborns and infants, prevalence rates in LAMI countries may be attributed to the higher prevalence of environmental risk factors for hearing impairment in these contexts (Olusanya & Newton, 2007). Such risk factors include infectious diseases; the use of ototoxic drugs; limited access to prenatal, perinatal and postnatal health care (Tucci et al., 2010); and pre- and postnatal infections such as rubella, measles and meningitis (Stevens et al., 2011). However, despite the estimated high incidence of hearing impairment in these countries, the causes have not been well documented.

The incidence of bilateral hearing impairment is estimated to be six or greater per 1 000 live births (Olusanya, Ruben, & Parving, 2006). This is in contrast to the lower incidence of bilateral, sensorineural hearing impairment, which is reported to be at a rate of two to four per 1 000 live births in high-income countries where NHS programmes are mostly well established (Tucci et al., 2010).

NHS pilot programmes in Nigeria have suggested a much higher prevalence of 28 per 1 000 live births. This rate is inclusive of all degrees of sensorineural hearing impairment and is thus by far the highest rate reported globally (Olusanya, 2011; WHO, 2010). In South Africa, it is estimated nationally that the prevalence of hearing impairment is four to six in every 1 000 live births in the public health care sector. This is approximately double the rate documented for the private health care sector, where a prevalence of three in every 1 000 has been estimated (Swanepoel & Störbeck, 2009). This higher estimated occurrence in the public health care sector highlights a greater need for audiological services in this sector in South Africa.

It is thus evident that prevalence rates differ within developing contexts and may be due to the differences in frequency of common risk factors for hearing impairment in each context, such as rubella, meningitis, measles and congenital cytomegalovirus. Risk factors like rubella, mumps and meningitis have become less common in some regions of the world, but have remained unchanged or increased in other regions (The Lancet, 2017). These differences in the incidence and prevalence of preventable conditions are probably due to a higher incidence of infections or diseases coupled with fewer maternal and child health programmes (Neumann et al., 2019). These risk factors highlight the importance of exploring preventative care and early detection of hearing impairment, which is key to facilitating the provision of timely diagnosis and intervention.