The standard assay for newborn CMV screening is rapid culture performed on saliva specimens, which cannot be automated, has been compared with rt-PCR assays performed on similar specimens.

Scientists at the University of Alabama (Birmingham, AL, USA) carried out a prospective, multicenter screening study of newborns comparing real-time PCR assays of liquid-saliva and dried-saliva specimens with rapid culture of saliva specimens obtained at birth. The infants were born at seven hospitals in the USA from June 2008 through November 2009.

A rapid-culture assay for the detection of early-antigen fluorescent foci, involving a monoclonal antibody against the major immediate early antigen of CMV, was used to detect CMV in saliva specimens. The rt-PCR protocol for dried-blood spots was performed to detect CMV DNA in saliva samples. A sample was considered positive if five or more copies per reaction were detected. The detection of CMV DNA was performed using the ABI 7500 Real-time PCR System (Applied Biosystems Inc, Foster City, CA, USA) and ABsolute QPCR Low ROX Mix (ABgene USA, Rockford, IL, USA).

A total of 177 of 34,989 infants were positive for CMV, according to at least one of the three methods. Of 17,662 newborns screened with the use of the liquid-saliva PCR assay, 17,569 were negative for CMV, and the remaining 85 infants had positive results on both culture and PCR assay. The sensitivity and specificity of the liquid-saliva PCR assay were 100% and 99.9%, respectively. Of 17,327 newborns screened by means of the dried-saliva PCR assay, 74 were positive for CMV, whereas 76 were found to be CMV-positive on rapid culture.

The authors conclude that saliva is a more reliable type of specimen than dried-blood spots for identifying congenital CMV infection by means of PCR assay and can be an effective tool for mass screening of newborns for CMV. Real-time PCR assays of both liquid-and dried-saliva specimens showed high sensitivity and specificity for detecting CMV infection and should be considered potential screening tools for CMV in newborns. The study was published online on June 2 2011, in the New England Journal of Medicine (NEJM).

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