PCR Saliva Tests Useful for Congenital CMV Screening

Real-time polymerase-chain-reaction (PCR) assays of saliva samples are accurate for detecting congenital cytomegalovirus infection in newborns, researchers found.

Assays using both liquid and dried saliva had high sensitivity and specificity for identifying the infection, with positive predictive values over 90% and negative predictive values at or near 100%, according to Suresh Boppana, MD, of the University of Alabama at Birmingham, and colleagues.

Unlike the standard rapid cultures of saliva and urine samples, the PCR assays can be automated and adapted for widespread screening, which could identify babies who would benefit from early intervention to mitigate the effects on speech and language development of any cytomegalovirus-related hearing loss, the researchers reported in the June 2 issue of the New England Journal of Medicine.

Although screening would allow for early identification, the standard culture method performed on saliva or urine samples cannot be automated, which limits utility for large-scale screening. Most infants with congenital cytomegalovirus infection are not identified because the infection is asymptomatic and testing is not routine. 

A previous study by Boppana's group showed the dried-blood-spot PCR assays identified fewer than 40% of cytomegalovirus-infected newborns, so the researchers compared real-time PCR assays (using either liquid or dry saliva samples) with rapid culture at seven U.S. hospitals.

Of those screened with the liquid-saliva PCR assay, 85 infants (0.5%) were positive on both rapid culture and the PCR assay. Another eight infants were positive on the PCR assay but not on culture. Of the 34,989 screened, 0.5% were positive for cytomegalovirus using at least one of the three screening methods. 

Of the newborns screened with the dried-saliva PCR assay, 76 (0.44%) were positive on rapid culture -- 74 of whom were also positive on the PCR assay. Another eight infants were positive on the PCR assay only. The sensitivity and specificity of the PCR assay were 100% and 99.9%, respectively, and the positive and negative predictive values were 91.4% and 100%, respectively. 

The sensitivity and specificity of the PCR assay were 97.4% and 99.9%, respectively, and the positive and negative predictive values were 90.2% and 99.9%, respectively.
Of the 16 infants who were positive on one of the PCR assays, but not on rapid culture, 13 underwent follow-up testing of saliva and urine samples; only three actually had a cytomegalovirus infection.

"Although false-positive saliva PCR results could lead to unwarranted parental anxiety and additional testing in infants to confirm or rule out congenital cytomegalovirus infection, the overall frequency of false-positive results for both liquid-saliva and dried-saliva PCR assays was less than 0.03%," they wrote. Those false-positives may have been the result of cytomegalovirus-containing maternal secretions in the infants' mouths, according to the researchers. 

"Nevertheless," they added, "when saliva PCR assay is used to screen newborns, a positive screening result should be confirmed within the first three weeks of age to avoid false-positive screening results."


Although the dried-saliva PCR assay failed to identify two infants who had the infection according to the standard rapid culture -- and the liquid-saliva PCR assay did not miss any -- the researchers suggested that using dried saliva may be preferable for screening.


"The simplified procedures for specimen collection, storage, and transport, combined with the high sensitivity, support dried-saliva PCR assay as a reasonable approach to cytomegalovirus screening in newborns," they wrote.


They acknowledged that the study was limited in that the infants who were found negative on initial testing were not enrolled in follow-up testing to confirm the absence of the infection.




Action Points:

• Explain that PCR testing of liquid or dried saliva was able to identify newborns with congenital cytomegalovirus infection with high sensitivity and specificity.
• Note that congenital cytomegalovirus infection is usually asymptomatic but can cause hearing loss; currently newborns are not screened for this infection.