Cytomegalovirus DNA detection in Guthrie cards: A powerful tool for diagnosing congenital infection

Background: A simple and reliable diagnosis of congenital cytomegalovirus infection is necessary both for clinical and epidemiological purposes. This could be accomplished through the demonstration of cytomegalovirus (CMV) DNA in blood spots (DBS) on Guthrie cards. Objectives: (1) To assess the sensitivity and specificity of the method (DBS test) in diagnosing congenital CMV infection compared with viral isolation and (2) to evaluate the applications of the test to the late diagnosis of congenital CMV. Study design: The method was tested on the cards of (1) 509 babies examined through viral isolation within their third week of life (72 positive cases) and (2) 191 children studied after 3 weeks of life (25 days to 5 years). Blood was eluted from Guthrie cards and heat extracted. The products of a nested polymerase chain reaction (PCR) amplifying one region in the CMV glycoprotein B (gB) gene were detected by agarose gel electrophoresis. Results: DBS test was positive in all 72 congenitally infected babies and in four of the 437 negative at cytomegalovirus isolation (sensitivity 100%, specificity 99%). Infection in 16 of the 92 infants with a late viral isolation was demonstrated to be congenital by the test, which also detected congenital infection in 18 of 83 children in whom viral culture was not performed (13 with and five without symptoms). Fifty-six additional control cases tested negative. Conclusions: DBS test is a reliable assay for diagnosing congenital cytomegalovirus infection and could be used as an alternative to viral culture. It is able to reveal whether ascertained CMV infection is congenital or postnatal at an age when viral isolation is not able to do so. It can assess the role of risky procedures such as transfusion and it can ascertain the etiology of morbid conditions diagnosed late or of controversial origin.