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As many as 6 percent of children born with Zika-induced microcephaly may have hearing loss, a new study from Brazil suggests.

And the authors warn that other children who were infected with the virus in their mothers’ wombs may be born with or may develop hearing problems, even if they do not have visible physical birth defects.


“Children with evidence of congenital Zika virus infection who have normal initial screening tests should receive regular follow-up, because onset of hearing loss could be delayed and the loss could be progressive,” the authors wrote.

The study is based on infants who were assessed for Zika-related birth defects at the Hospital Agamenon Magalhães, in Pernambuco, Brazil. It was published Tuesday in Center for Disease Control and Prevention’s online journal Morbidity and Mortality Weekly Report.

Experts have been warning that the kind of brain damage wreaked by the Zika virus could result in vision and hearing loss.


Other viruses such as rubella and cytomegalovirus (CMV) that can trigger microcephaly when contracted in the womb also lead to hearing loss in some cases.

This study looked at the test results of 70 children with microcephaly and confirmed Zika infection who were referred to the hospital for a hearing assessment. The hospital is a reference center for diagnosis of hearing loss and hearing rehabilitation.

The children were tested at range of ages, the youngest only 16 days old and the oldest 10 months old.

One child who had profound hearing loss in both ears had a twin brother who tested negative for Zika antibodies and appeared untouched by the virus.

Five children had hearing loss, though one of them had been treated for a blood infection with an antibiotic that can cause damage to ears. Taking that child out of the calculation suggests that hearing loss in Zika-induced microcephaly occurs in about 6 percent of cases.

The authors note their findings could downplay the frequency in which hearing loss occurs in children infected with Zika in the womb because they only tested children with microcephaly, which is characterized by an abnormally small head and in some cases brain damage.

“It is possible that the full spectrum of congenital Zika virus infection includes children without microcephaly but with auditory deficits, as occurs with congenital rubella and CMV infections, in which children born with no apparent structural anomaly can be found to have hearing loss at birth or later in life,” they wrote.

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