Saliva Culture Superior to Neonate Molecular Screening for CMV

A molecular screening test, using heel-prick blood, was not consistently sensitive enough to detect a congenitally transmitted viral infection in neonate blood samples. The samples collected on filter paper are routinely used to test for metabolic and genetic diseases.

The test using real-time polymerase chain reactions (RT-PCR) on dried blood samples (DBS) were compared with saliva culture methods to detect Cytomegalovirus (CMV). The key feature of the RT-PCR procedure is that the amplified DNA is detected as the reaction progresses in real time rather than at the end of the process. The common methods for detection of products in real-time PCR use either nonspecific fluorescent dyes that intercalate with any double-stranded DNA, or sequence-specific DNA probes consisting of oligonucleotides that are labeled with a fluorescent reporter. Single-primer and two-primer RT-PCR systems were used to detect the fluorescent copies of the CMV DNA. The results were published online on April 2010 in the Journal of the American Medical Association (JAMA).



The samples were collected from infants born at seven United States medical centers as part of the National Institute on Deafness and Other Communication Disorders' CMV and Hearing Multicenter Screening (CHIMES) Study (NIDCD; Bethesda, MD, USA). Blood samples taken by heel pricks from neonates are routinely tested for such diseases as hyperthyroidism and sickle cell anemia and could therefore also be used in this study. As CMV infection is a leading cause of sensorineural hearing loss, both of which may be unapparent in the newborn, and at present, the only way to detect the virus is the labor-intensive tissue culture method.

The lead team at the University of Alabama at Birmingham Hospital (Birmingham, AL, USA), tested the diagnostic accuracy of the RT-PCR system for CMV in 20,448 babies. The saliva culture method detected 91/92 that were confirmed to have congenital CMV infection. The single primer RT-PCR was used on 11,422 samples could only detect 17/60 confirmed cases, while the 2-primer set found only 11 positives from the 32 proven cases of the 9,026 samples screened.

In the United States there are an estimated 20,000 to 40,000 babies born each year with congenital CMV. Hearing loss may occur in 10% to 15% due to the inapparent infections, which may have a late or progressive onset. Suresh Boppana, M.D, coprincipal investigator of the study, said "that a screening test needs to have a sensitivity of at least 95%" and therefore the 30-40 percent achieved on the dried blood meant more than half the infection would have been overlooked. A new study is in progress to test RT-PCR screening of saliva, which is known to be full of viruses in babies with congenital CMV. The saliva examination is noninvasive and needs minimal processing.

Related Links:
National Institute on Deafness and Other Communication Disorders
University of Alabama at Birmingham Hospital