Primary cytomegalovirus (CMV) infection in pregnancy: Diagnostic value of CMV PCR in saliva compared to urine at birth

Background: Due to its ease of collection saliva was recently recommended as the preferred specimen, not only for screening, but also for diagnosis of congenital cytomegalovirus (CMV) infection. Objective: To compare the diagnostic performance of saliva PCR to urine PCR in infants born to mothers with primary CMV infection during pregnancy. Study design: We retrospectively analyzed available data of infants tested for CMV DNA in urine and saliva at birth. PCR was performed with RealStar (R) CMV-PCR Kit 1.0 (altona Diagnostics). Infectious virus was detected in urine by rapid culture. Results: A total of 133 newborns were eligible for final analysis. Saliva swabs and urine were collected at birth with a time interval of 0-8 days (median 0; IQR 0-1). In 55% of newborns, cord blood was also tested. The overall concordance of saliva and urine PCR was 91% (27 positive, 94 negative). In 12 cases with discordant findings the discrepancy was due to false-negative (n = 2) or false-positive (n = 10) PCR results in saliva. Compared to urine, PCR in saliva showed a positive predictive value of 73%. Viral load in saliva was significantly lower (p < 0.0001; Mann-Whitney test) in the 10 false-positive cases than in the 27 cases with concordantly positive results. Conclusions: Positive CMV PCR results in saliva, especially low positive, have to be confirmed by urine testing. In our opinion detection of CMV by PCR in neonatal urine remains the gold standard for diagnosing congenital CMV infection in infants of mothers with primary infection in pregnancy.