Some child hearing loss tied to virus in pregnancy

Hearing loss in a child may have links to a virus that Mom got while she was pregnant, according to a new study.

In kids that had some degree of hearing loss, about 9 percent also had cytomegalovirus (CMV) at birth, says a new study in the Archives of Otolaryngology-Head and Neck Surgery.

“(CMV) needs to be on the list of things we think about when we see a child with hearing loss,” said Dr. Stephanie Misono, an ear, nose and throat fellow at Vanderbilt University in Nashville, and lead author on the study.

CMV is a common virus that normally causes a harmless infection, although people with weakened immune systems can get sick from it. Infections can be avoided by washing your hands regularly especially after dealing with sick people and toddlers, who sometimes carry it, according to the Centers for Disease Control.

For women who are already infected when they become pregnant, the chances of passing it along to their children are quite small. It’s women who pick it up while pregnant who have a higher chance, according to the study, but it’s still quite unlikely that their babies will develop CMV-related hearing loss.

Up to one in 1,000 children have some kind of serious hearing loss, meaning that they can’t hear ordinary conversation, according to the American Speech Language Hearing Association. About half of these cases are hereditary.

For parents that have no hearing loss, this helps to at least find out why this might have happened in their child, Misono said. However, there is no effective treatment or vaccine, and the study was not designed to determine whether CMV actually causes hearing loss.

Past studies showed a link between hearing loss and CMV, but there haven’t been any that looked at kids with hearing loss and tried to determine if it came from a CMV infection.

Up to one in 25 women will get CMV while they’re pregnant, which is when it’s risky for the baby. It’s been linked to several developmental issues in children, including mental retardation and cerebral palsy. Hearing loss is the most common problem.

If a woman gets CMV while she’s pregnant, she has about a 33 percent chance of passing it along to her baby, according to the CDC.

But about half of women have already had it by the time they get pregnant. There’s less than a one percent chance of passing it along to your unborn baby if this is the case, said Karen Fowler, who studies childhood infections at the University of Alabama in Birmingham, and who did not work on this study.

This study looked at 354 kids 4 years and older who were tested for CMV at birth. All of these children had hearing loss, and 34 of them had CMV they had gotten from their mothers.

The degree of hearing loss varied from partial impairment in one ear to total deafness, but kids that had CMV at birth had more severe hearing loss than their CMV-negative peers. Also, a higher percentage of those with CMV had hearing loss in only one ear. Misono said it’s unclear why this is.

Researchers don’t know why being exposed to CMV in utero might cause hearing problems in kids later, but the virus could be doing some kind of damage, said Fowler. Babies who get CMV after they’re born have no increased risk of hearing loss.

Knowing how exactly CMV causes hearing loss is important if a treatment is going to be developed, Misono said.

SOURCE:  Archives of Otolaryngology-Head and Neck Surgery, online January 17, 2011.

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