4Causes & risk factors in India

FA different mix of causes

A textbook of cochlear implantation written in Europe or North America will list age-related and genetic loss as the dominant causes, with infection a historical footnote. In India the order is rearranged. Infective and birth-related causes loom far larger, congenital deafness is amplified by patterns of marriage, and acquired causes — noise and ototoxic drugs — act on a young, large, and often unprotected population. Reading Western causal data onto Indian patients misleads; the local pattern must be understood on its own terms.

FTThe map of causes

The causes fall into a handful of groups. Chronic ear disease — long-standing middle-ear infection with a discharging, perforated drum — is the signature Indian cause and a leading source of preventable conductive and mixed loss. Congenital and genetic causes account for a large share of severe childhood deafness, raised by the high rate of consanguineous marriage in some communities. Birth-related injury — prematurity, low birth weight, birth asphyxia, neonatal jaundice and infection — adds further childhood cases wherever delivery and newborn care are limited.

Among acquired causes, noise (occupational, traffic, and recreational), ototoxic drugs (aminoglycosides — including those used for tuberculosis — and platinum chemotherapy), and vaccine-preventable infections (measles, mumps, rubella, and meningitis) each contribute, alongside the universal rise of age-related loss as the population lives longer.[2012]

FTPreventable, treatable, or neither

The most useful way to sort these causes is by what can be done about them. A large majority of the Indian burden is preventable (by immunisation, safe birth, noise control, and avoiding ototoxic exposure) or treatable at the primary level (by managing ear infection and removing wax) — needing no cochlear implant at all. The implant is reserved for the residue: severe-to-profound sensorineural loss, much of it congenital or genetic, where the cochlea cannot be repaired and the signal must be delivered electrically.

CCauses across the life course

The causes also sort by age, which is why the burden is bimodal (Module 3). Before and at birth: genetic and perinatal causes. In childhood: chronic ear disease and vaccine-preventable infection. In working life: noise and ototoxic exposure. In later life: presbycusis. A child presenting with deafness and an adult presenting with it are, in effect, products of different epidemiologies — and the implant team reads the likely cause partly from the age at which hearing failed.

FWhat the next modules examine

The remaining causal modules take the largest and most distinctively Indian contributors in turn: chronic ear disease and the preventable conductive burden (Module 5); noise and ototoxicity, the acquired sensorineural causes (Module 6); consanguinity and the genetics of deafness (Module 7); and congenital and childhood hearing loss as a whole (Module 8). We begin with the draining ear that fills Indian ENT clinics: chronic ear disease.