Diagnosis of congenital CMV infection via dried blood spots

Cytomegalovirus (CMV) infection is the most frequent congenital infection in humans and can cause permanent damage--particularly neurological--in about 20% of those infected, with or without symptoms at birth. Laboratory diagnosis is essential on account of the relatively non-specific clinical manifestations in symptomatic newborns but also because of the high frequency of asymptomatic cases that are nevertheless at risk of lesions later in life. However, these tests need samples taken within 3 weeks of birth to distinguish congenital infection from the more common, but clinically benign, perinatal infection. Tests for viral DNA have proved a valid means of diagnosing congenital CMV infection in neonatal blood dried on paper (DBS) widely used in screening for metabolic and genetic diseases, as an alternative to the conventional urine culture method. The DBS test is simpler, faster and less costly than viral isolation; in addition the samples can be safely stored for long periods, so diagnosis can be made even after several years. The sensitivity and specificity of the DBS test, compared to the reference method, have been reported to range between 71 and 100% and 99 and 100%, respectively, depending on the different studies and diagnostic criteria applied. The most interesting applications reported so far involve retrospective determination of the impact of congenital CMV in sensorineural deafness, abnormalities of cortical development, neonatal cholestasis and surveys of the prevalence of this infection in various populations. The test might be useful in the future for neonatal screening with a view to treating neonates and so avoiding the damage this disease can cause.