Feasibility, performances and predictive value of congenital CMV neonatal screening on saliva swabs.

Background: Early diagnosis of congenital CMV infection (cCMVI) allows for early intervention and follow-up to detect delayed hearing loss. While CMV PCR in urine is the gold standard for cCMVI diagnosis, saliva testing is often performed.

Objectives: Our aim was to determine (i) if swab saliva sampling needed standardization, (ii) if a threshold value in "virus copies per million cells (Mc)" in saliva samples could improve clinical specificity, and (iii) to establish a correlation between viral load in saliva and symptomatology/outcome of cCMVI.

Materials And Methods: In our institution, universal newborn screening is performed on saliva swabs at delivery or until day 3 of life. If positive, CMV PCR in urine is done within 2 weeks to confirm or exclude cCMVI.

Results: Cell quantification showed that saliva swab sampling was well performed as 95.4 % samples had more than 100 cells/10 µL. There was a good correlation between saliva viral load in copies/mL and in copies/Mc (Pearson's r = 0.96, p < 0.0001). However, threshold values, established to determine a viral load level at which we could confidently identify infected newborns, did not improve positive predictive value (21.8 % for copies/mL and 21 % for copies/Mc vs 25.4 % without threshold) but instead reduced sensitivity (88 % and 85% vs 100 % without threshold). Samples collected on day 2 or 3 had better positive predictive value (38.7 %) compared to those collected on day 1 (23.8 %). Symptomatology at birth was not significantly associated with viral load in saliva at diagnosis. However, sequelae occurrence was associated with viral load in saliva (copies/Mc).

Discussion: Our results confirm that saliva swab is a suitable sample for universal neonatal screening. However, identifying newborns that will develop sequelae remains an issue in the management of cCMVI.