While microcephaly is the most obvious, dramatic, and medically devastating presentation of Congenital Zika Syndrome, the full spectrum of congenital defects caused by maternal infection with the Zika virus isn't yet known.
Some are beginning to come to light (see Brazil: Expanded Spectrum of Congenital Ocular Findings in Microcephaly and BMJ: Congenital Zika Syndrome with Arthrogryposis), but other - more subtle defects - may not become obvious for months or years.
Today in an Early Release, the CDC's MMWR reports that researchers have tested 70 children with both microcephaly and evidence of Zika infection in Brazil, and found 5.8% had hearing loss without other potential cause.
Since this study only looked at microcephalic cases, it doesn't tell us much about the potential for hearing loss in children with less pronounced Zika congenital Syndrome symptoms, although researchers suspect they too may be at elevated risk for hearing loss.
It's a long, detailed report. So I've only posted the Summary, and some excerpts from the discussion. Follow the link to read it in its entirety.
What is already known about this topic?
Congenital Zika virus infection is characterized by microcephaly and other abnormalities of the brain and eye; orthopedic lesions have also been documented. While the full clinical spectrum of the syndrome is not yet known, the neurologic damage and corresponding radiologic brain imaging have been well described. Other congenital infections can cause hearing loss, which is diagnosed at birth or during later follow-up; however, few data exist regarding hearing loss associated with confirmed congenital Zika virus infection.
What is added by this study?
Congenital infection with Zika virus appears to be associated with sensorineural hearing loss. Among 70 children with microcephaly and laboratory evidence of congenital Zika virus infection, four of 69 (5.8%) were found to have sensorineural hearing loss without other potential cause.
What are the implications for public health practice?
Congenital infection with Zika virus should be considered a risk factor for hearing loss. Children with evidence of congenital Zika virus infection who have normal initial screening tests should receive regular follow-up, because onset of hearing loss associated with other congenital viral infections can be delayed and the loss can be progressive.
Hearing Loss in Infants with Microcephaly and Evidence of Congenital Zika Virus Infection — Brazil, November 2015–May 2016
Early Release / August 30, 2016 / 65
Mariana C. Leal, PhD1,2; Lilian F. Muniz, PhD2; Tamires S.A. Ferreira, MD1; Cristiane M. Santos, MD1; Luciana C. Almeida2; Vanessa Van Der Linden, MD3,4; Regina C.F. Ramos, MD5; Laura C. Rodrigues, PhD5; Silvio S. Caldas Neto, PhD2 (View author affiliations)
In this report of complete auditory function evaluation in a series of 70 children with microcephaly and laboratory evidence of congenital Zika virus infection, five (7.1%) infants had sensorineural hearing loss. The hearing loss varied in severity and laterality, which has been reported in hearing loss associated with other congenital infections (6,7).
If the one infant with bilateral profound sensorineural hearing loss who had been treated with amikacin (a known ototoxic antibiotic) before the hearing testing is excluded, the proportion of infants with sensorineural hearing loss was 5.8% (four of 69). This proportion, although lower than the 9% reported from a small sample of newborns with microcephaly associated with presumed Zika-virus infection tested by otoacoustic emissions (4), is within the range (6%–65%) reported for other congenital viral infections (6,7).
In the majority of cases of hearing loss associated with congenital viral infection, the damage to the auditory system is within the cochlea (7). It is likely that similar lesions account for the hearing deficit in children with congenital Zika virus infection, although histologic studies are needed to confirm this. However, a concomitant central origin cannot be discounted, and behavioral auditory evaluation might provide additional information.
The findings in this report are subject to at least two limitations. First, auditory behavioral tests, in which an infant’s responses (e.g., quieting, eye-widening, or startle) to various calibrated sounds are recorded, and which can complement the hearing evaluation and provide information about processing of auditory signals, were not used.
Second, this series includes only children with microcephaly. It is possible that the full spectrum of congenital Zika virus infection includes children without microcephaly, but with auditory deficits, as occurs in 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.
(Continue . . . )