The most common medical cause of both early- and delayed-onset hearing loss in infants is which infection?

• A. Cytomegalovirus
• B. Herpes simplex virus
• C. Rubella
• D. Toxoplasmosis

Answer: (A)

Cytomegalovirus infection is the most common infectious cause of sensorineural hearing loss in infants, and it can affect hearing both at birth and emerge later in childhood. The virus is the leading cause of congenital infection, and among those infants the risk of hearing loss is substantial. Importantly, the loss can be present early or appear as a delayed-onset deficit even in infants who seem healthy at birth, because CMV can cause ongoing damage to the cochlea and auditory pathways or reactivation over time.

Rubella used to be a major cause of congenital deafness, but vaccination has greatly reduced its incidence, making it less likely today. Toxoplasmosis and herpes simplex virus can cause congenital infections with various sequelae, but they are less commonly the source of infant hearing loss compared with CMV.