Infection-Related Hearing Loss

Definition and epidemiology

Infection-related hearing loss arises when infections passed to the baby in pregnancy (congenital) or acquired after birth damage the inner ear and auditory nerve pathways. Viruses can damage inner ear structures directly, cause harm through the inflammatory response, or make the ear more vulnerable to bacterial and fungal infection; the loss is usually sensorineural, although some infections cause conductive or mixed loss (Cohen et al., 2014).

Congenital cytomegalovirus (CMV) is the most common non-hereditary cause of childhood sensorineural hearing loss. In developed countries 0.58% of newborns have congenital CMV; 9.8% of infected babies are symptomatic at birth, and hearing loss develops in about 33% of symptomatic and 9.9% of asymptomatic babies (Goderis et al., 2014). In Türkiye, CMV seropositivity in pregnant women has been reported at 85-100% and the frequency of congenital CMV in newborns at 0.2-1.19% (Bülbül and Hacımustafaoğlu, 2022). Such high seropositivity suggests that many affected babies may be infected through maternal reinfection or reactivation; hearing loss rates were similar after primary and non-primary maternal infection (12.1% and 11.8%) (Goderis et al., 2014).

Symptoms and signs

In congenital CMV the course of hearing loss varies. In symptomatic children the loss is bilateral in 71.2% and delayed in onset in 18.1%; in asymptomatic children 57% of losses are unilateral and 9% are delayed. The loss progresses in about one in five to six children and fluctuates in about one in four to five (Goderis et al., 2014). A baby with normal hearing at birth can therefore develop hearing loss later.

Profound hearing loss is a major consequence of bacterial meningitis. When inflammation reaches the labyrinth, fibrosis and calcification can develop in the cochlea and may obliterate it, limiting the success of cochlear implantation (Merkus et al., 2010). In mumps, the loss is usually unilateral and sometimes reversible but can be severe and permanent; its frequency has been reported at between 1 in 1,000 and 1 in 30,000 cases (Cohen et al., 2014). For loss of sudden onset, follow the approach in sudden hearing loss.

Before widespread vaccination, measles accounted for 5-10% of cases of profound hearing loss in the United States; in congenital rubella, sensorineural loss is the most common lasting sequela and occurs in 58% of cases. In Ramsay Hunt syndrome, caused by varicella zoster, ear vesicles and facial palsy may be accompanied by sensorineural loss (24%), tinnitus (48%) and vertigo (30%); auditory symptoms have been reported in 14-49% of people living with HIV (Cohen et al., 2014). Where dizziness dominates inner ear involvement, see vestibular neuritis and labyrinthitis.

Causes and risk factors

Risk depends largely on the type of infection, when it occurs and the protective measures in place. In pregnancy, CMV, rubella, toxoplasmosis, syphilis and herpes infection, and after birth, bacterial or viral meningitis and encephalitis are recognised risk factors for permanent childhood hearing loss (Joint Committee on Infant Hearing [JCIH], 2019). Widespread use of mumps, measles and rubella vaccines has markedly reduced hearing loss from these infections, while hearing loss reported after measles vaccination occurs at about one case per 6-8 million doses, with no causal link established (Cohen et al., 2014).

In meningitis, bacteria and inflammatory mediators reaching the inner ear can cause labyrinthitis, followed by fibrosis and new bone formation (Merkus et al., 2010). Drugs used during treatment, such as aminoglycosides, can also affect hearing; prolonged aminoglycoside use is a separate JCIH risk factor (JCIH, 2019). For drug-related loss, see ototoxicity.

Evidence on a link between COVID-19 and hearing loss, tinnitus and vertigo should be interpreted with caution. The pooled estimates of the first systematic review (hearing loss 7.6%, tinnitus 14.8%, vertigo 7.2%) relied largely on retrospective recall, and it was often unclear whether a symptom was new. The authors of the included studies were therefore contacted to clarify whether symptoms were new, and a new meta-analysis was carried out with more conservative inclusion criteria (Lough et al., 2022). Controlled studies based on audiometric measurement remain limited.

Audiological and clinical assessment

In infection-related loss, the audiologist’s main task is to detect hearing loss at the right time and prevent loss to follow-up. JCIH (2019) recommends monitoring infants at risk even if they pass newborn hearing screening: in congenital CMV, a diagnostic assessment no later than 3 months of age and yearly checks to age 3; after bacterial or viral meningitis, a diagnostic assessment no later than 3 months after the illness and yearly checks to school age; and after in utero herpes, rubella, syphilis or toxoplasmosis, a diagnostic assessment by 9 months. Caregiver concern about hearing or speech calls for immediate referral at any age (JCIH, 2019).

• Diagnosing congenital CMV: virus PCR on urine or saliva must be positive in a sample taken within the first 21 days of life; later samples cannot distinguish postnatal infection (Rawlinson et al., 2017). Targeted CMV testing of babies who do not pass newborn hearing screening makes it possible to meet this window; in a multicentre study 7% of CMV-positive babies did not pass screening, and the targeted approach identified 57% of CMV-related loss present in the neonatal period (Fowler et al., 2017).
• Test battery in infants and young children: frequency-specific ABR for threshold estimation, OAE, high-frequency (1000 Hz) tympanometry and age-appropriate behavioural tests (visual reinforcement audiometry, conditioned play audiometry). Because the loss may start in one ear, each ear must be assessed separately; see unilateral hearing loss.
• After meningitis: repeated audiological testing and early MRI, with urgent referral to a cochlear implant centre for sensorineural loss greater than 30 dB (Merkus et al., 2010). Loss of cochlear fluid signal on MRI and new bone on CT suggest ossification, although preoperative imaging does not always show it accurately (Singhal et al., 2020).
• Acquired viral loss: pure-tone and speech audiometry, tympanometry and acoustic reflexes; vestibular tests (vHIT, caloric testing, VEMP) in Ramsay Hunt syndrome and labyrinthine involvement.
• Laboratory tests: serology as indicated; treatable causes such as syphilis may be investigated by the physician in unexplained sensorineural loss.

Treatment and audiological rehabilitation

Congenital CMV: in a randomised trial in newborns with symptomatic congenital CMV, six months of valganciclovir, compared with six weeks, increased the proportion with normal or improved hearing at 24 months (77% versus 64%) and improved language scores; no short-term hearing improvement was shown, and severe neutropenia occurred in both groups (Kimberlin et al., 2015). Consensus recommendations support six months of treatment started within the first month of life in moderately to severely symptomatic newborns (Rawlinson et al., 2017). Evidence is limited for babies with isolated hearing loss or no symptoms. Decisions on treatment, dosing and monitoring rest with the paediatric infectious diseases physician.

Bacterial meningitis: the Dutch cochlear implant group protocol includes dexamethasone before antibiotics, early MRI, repeated audiological follow-up and urgent referral to a cochlear implant (CI) centre for loss greater than 30 dB, with the aim of intervening before ossification develops (Merkus et al., 2010). In a systematic review of 610 patients implanted after meningitis, auditory outcomes improved in all studies; absence of ossification, full electrode insertion, shorter duration of hearing loss and no neurological sequelae were linked to better results, and early bilateral implantation was recommended (Singhal et al., 2020).

Other infections: vaccination is the most effective approach for mumps, measles and rubella (Cohen et al., 2014). Medical treatment of Ramsay Hunt syndrome, HIV and syphilis is planned by the relevant physician. For permanent loss, hearing aids, CROS or bone conduction implants for unilateral loss, and CI for severe to profound loss are considered. Children at risk continue to be monitored according to the JCIH schedule.

Impact on quality of life and advice

Infection-related hearing loss often follows a serious illness or a period of neonatal intensive care, and families may have to manage developmental and neurological problems alongside hearing loss. In children with congenital CMV, the possibility that hearing loss may appear or progress later creates uncertainty for parents; regular monitoring and clear information help to reduce this anxiety. Profound loss developing rapidly after meningitis means a sudden break in communication and calls for psychosocial support.

Practical advice:

• Keep your child’s vaccinations up to date, particularly measles, mumps and rubella.
• During pregnancy, reduce CMV exposure by washing hands after contact with young children’s saliva and urine and by not sharing food or drinks.
• Do not miss follow-up appointments for a child at risk, even after a newborn screening pass; loss to follow-up is one of the most common problems.
• For unilateral loss, arrange classroom seating so that the better ear faces the speaker, and use a remote microphone system.
• You can follow your child’s language and speech development with the questionnaires below.