It's long been known as a major cause of hearing loss in children, but researchers are still trying to come up with a test to accurately detect cytomegalovirus (CMV) in newborns, a virus transmitted from an infected mother to her baby before birth. In a study published in the April 14, 2010 issue of the Journal of the American Medical Association, researchers this time conducted DNA screening of newborn blood samples, using dried blood spots—typically drawn through a heel stick, these samples are collected from all infants born in the US to conduct metabolic screening.
While researchers had high hopes that DNA testing would prove to be a quick, easy screening tool, results showed that DNA analysis ended up missing approximately two-thirds of CMV infections. What did work? Saliva screening had better CMV detection rates (salivary glands tend to harbor the virus), but researchers note this type of testing is not yet suitable for mass screening.
"As the disease ... remains a significant public health problem, there continues to be a need to identify the large number of infants with ... CMV infection early in life," writes lead researcher Dr. Suresh B. Boppana, of the University of Alabama at Birmingham (quoted in a HealthDay article on the study). "The results of our study underscore the need for further evaluation of ... methods performed on saliva or other specimens that can be adapted to large-scale newborn CMV screening."
Each year in the US, 20,000 to 40,000 infants are born with CMV infection. Up to 95 percent of babies have no obvious signs of the virus at birth. The ability to identify children at increased risk for CMV-associated hearing loss early in life would enable doctors to intervene at critical stages of speech and language development, researchers note.
Before they are discharged from the hospital, almost all US newborns receive an auditory screening test to check for hearing loss. According to the Boys Town National Research Hospital (a specialist in newborn hearing research), the most commonly administered test checks otoacoustic emissions (OAEs).
When babies take the test, a miniature earphone and microphone are placed in one ear and sounds are played. If hearing is normal, an echo is reflected back into the ear canal and is measured by the microphone. When a baby has a hearing loss, no echo can be measured. A second test—auditory brainstem response (ABR)— may also be administered. For this test, Band-Aid like electrodes are placed on the baby's head. When sound is played, the electrodes measure how strongly newborn hearing nerves respond to sound.