Quantitative assessment of viral load in the blood and urine of patients with congenital cytomegalovirus infection using droplet digital PCR

Congenital cytomegalovirus infection (cCMV) is a common cause of congenital infections, leading to neurodevelopmental sequelae. Real-time quantitative polymerase chain reaction (qPCR) has been widely used for the diagnosis and assessment of cCMV; however, the correlation between CMV DNA load and the severity of cCMV symptoms has been inconclusive. Droplet digital PCR (ddPCR) offers an improvement over the current qPCR methods through the absolute quantification of viral loads. We compared ddPCR and qPCR results for the quantification of CMV DNA in blood and urine specimens from 39 neonates with cCMV (21 symptomatic and 18 asymptomatic). There was no significant difference in blood CMV DNA loads measured by ddPCR and qPCR, with or without any clinical findings. However, developmental delays at 36 months were significantly more frequently observed in patients with high CMV DNA loads (≥2950 copies/ml), as measured by ddPCR at diagnosis, than in those with lower CMV DNA loads. The association of urine CMV DNA load with symptoms and developmental delay was not observed. CMV DNA loads in the blood might be used as a predictor of developmental outcomes in cCMV patients, and absolute quantitation of viral loads by ddPCR assay could contribute to the standardization of CMV load measurement.