by Nancy Shute
Babies who are born infected with cytomegalovirus, a common virus, can suffer permanent hearing loss, but newborns aren't routinely tested to see if they have it. That could change if a pediatrician at the University of Alabama in Birmingham has his way.
He's the leader on a new study that found that a simple saliva test can identify babies at risk. But testing all babies for cytomegalovirus is probably not going to happen anytime soon.
About 1 in 150 babies are born infected with the virus, according to the federal Centers for Disease Control and Prevention. The virus is considered a major cause of hearing loss, second only to genetic causes.
About 20 to 40 percent of early childhood hearing loss is probably caused by CMV, according to Suresh Boppana, the professor of pediatrics at UAB who is lead author on the new study, which involved seven academic medical centers around the county. It was published Wednesday in the New England Journal of Medicine.
But since only 10 percent of babies who are infected with CMV show any symptoms of illness, most parents aren't aware that their children have it. About 2,000 to 4,000 children in the United States have hearing loss caused by CMV each year.
Thus the need for a screening test. The existing test for CMV in babies requires a sample of the baby's saliva or urine. Laboratories then put the sample in a dish with live cells, and let them grow. That's too complex for a routine screening test. The researchers had earlier tried to use the blood spot samples that hospitals gather from newborns to test for CMV, but found that it identified less than half of infected children.
Then they tried a laboratory workhorse, the polymerase chain reaction (PCR) test. It's used to identify small bits of DNA, and is used in dozens of medical tests, including HIV tests and prenatal genetic testing. Boppana and his colleagues used PCR to identify CMV in dried samples of saliva, taken from babies by putting a swab in their mouths. They tested about 35,000 babies. The test was 97 percent accurate in identifying babies infected with the virus.
"The dry saliva is much more user-friendly," Boppana told Shots. He figures that the test would cost about $3, about half the cost of the tissue culture method. He hopes that the new test could lead to universal testing of newborns.
"Right now most babies with congenital CMV are not being detected," he says. Once identified, children with CMV should have hearing tests at least once every six months, because hearing loss caused by the virus may not happen until a child is four years old. The sooner a child with hearing loss can start getting help with hearing aids or speech therapy, the more likely she or he will be able to develop speech and language.
There is no treatment for CMV infection in small children that could be used widely, unfortunately. Antiviral drugs used in adults are toxic, and have been used in children only in the rare cases where a child becomes seriously ill.
Although newborns are screened for dozens of diseases and genetic disorders while still in the hospital, adding another test to the roster, which are determined by each state, is no easy matter. Still Boppana is optimistic that will happen. "We do think it's a good screening test for all babies."