The heel-stick test commonly used for screening newborns for a variety of genetic disorders is not a good way to test for cytomegalovirus infections, the most common nongenetic cause of hearing loss, researchers reported Tuesday. About 20,000 to 30,000 infants in the U.S. are born with cytomegalovirus (CMV) infections acquired from their mother each year, and about 10% to 15% of them go on to develop hearing loss. Detection of the virus at birth could sharply reduce the infections, which often have no symptoms, and researchers had high hopes for the heel-stick test, which is already widely used. In it, a needle is used to prick the infant's heel, producing a drop of blood that is absorbed onto a filter paper and dried. A variety of tests can then be run on the dried blood.
The only accurate way now to identify a CMV infection is to culture a urine or saliva specimen to look for the virus. But that is cumbersome, time-consuming and relatively expensive. Researchers had hoped that it would be possible to use DNA screening techniques to look for the viral genes in the blood obtained by heel sticks.
To test this possibility a team of researchers headed by Dr. Suresh B. Boppana of the University of Alabama at Birmingham screened blood samples from the university and six other institutions. Among 29,448 babies screen with the conventional culture technique, the team reported in the Journal of the American Medical Assn., they found 91 cases of congenital CMV infections. Subsequent diagnoses by the infant's own doctors found that 92 had the virus, for a detection rate of nearly 100%. In contrast, among 11,422 infants screened with a DNA assay, they identified only 28.3% of infections. Among another 9,026 infants who were given what researchers hoped would be a more sensitive DNA assay, the team identified only 34.4% of infections.
"These results have major public health implications because they indicate that such methods, as currently performed, will not be suitable for the mass screening of newborns for congenital CMV infections," they wrote. Researchers will now have to look elsewhere for a suitable test.
-- Thomas H. Maugh II