Study Finds PCR Saliva Tests Promising for Newborn CMV Screening

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July 13, 2011

Congenital cytomegalovirus (CMV) infection is a cause of hearing loss in infants, but newborn screening is not routinely performed in the United States. Current methods of testing, such as culture of saliva, cannot be automated, making it impractical for screening large populations. A study published in the June 2nd issue of the New England Journal of Medicine, however, reported encouraging findings from analysis of a new method for detecting the infection that uses liquid or dried saliva samples from newborns. It could potentially allow for automation for widespread use, leading to better identification of newborns with CMV infection and earlier intervention to prevent hearing loss.

CMV is a common virus in the herpes family. As many as 50-85% of adults in the US have been infected. Most people are infected as children or young adults and do not experience any significant symptoms or health problems. CMV is found in many body fluids during an active infection and is easily transmitted to others through close physical contact or by contact with infected objects. After an initial infection has resolved, CMV becomes dormant, remaining in the person for the rest of their life without causing any symptoms, unless it becomes reactivated when their immune system is weakened.

For infants, however, a primary CMV infection can be serious. If a woman becomes infected with CMV for the first time just before or during pregnancy, there is a possibility that she may pass the infection on to her unborn baby, a condition known as congenital CMV infection. Although usually asymptomatic at birth, congenital CMV infection can cause hearing loss and is associated with physical and developmental problems that may appear months later, including visual impairment, learning difficulties, and seizures.

Currently, newborns are not regularly screened for CMV infection in the US. Testing may be performed on a newborn if certain signs are present, including jaundice, anemia, an enlarged spleen and/or liver, and a small head, or on an infant with hearing and vision problems, pneumonia, seizures, and/or signs of delayed mental development. A CMV screening test for all newborns at birth would allow those who are infected but asymptomatic to be identified and monitored so that appropriate intervention could be provided. A standard test for congenital CMV infection is rapid culture of a saliva specimen obtained at birth. However, cultures cannot be automated, so the method is not suitable for screening a large population.

An alternative is to detect the DNA of the virus in saliva using a rapid polymerase chain reaction (PCR) test that does not need extraction of the DNA. This method can be automated. To compare the performance of rapid culture of saliva specimens obtained at birth with real-time PCR assay of both liquid and dried saliva specimens, researchers for the National Institute on Deafness and Other Communication Disorders CHIMES Study conducted a multicenter screening study of nearly 35,000 newborns. They found that PCR had high sensitivity and specificity for detecting CMV. Taking rapid culture as the 'gold standard', liquid saliva PCR correctly identified 100% of those with CMV and correctly excluded 99.9% of those without CMV. Dried saliva PCR correctly identified 97.4% of those with CMV and correctly excluded 99.9% of those without it.

The authors concluded that both PCR assays should be considered potential screening tools for CMV infection in newborns. While testing of liquid saliva samples performed slightly better than dried saliva samples, using dried samples has advantages in terms of collection and storage that may make it the preferred method since both methods were found to have high sensitivity. The researchers would still recommend confirmatory testing of positive results within 3 weeks of birth to rule out false positives.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Neale, Todd. Staff Writer, MedPage Today. PCR Saliva Tests Useful for Congenital CMV Screening. Available online at http://www.medpagetoday.com/Pediatrics/GeneralPediatrics/26805?utm_content=&utm_medium=email&utm_campaign=DailyHeadlines&utm_source=WC&userid=238737 through http://www.medpagetoday.com. Accessed June 2011. 

Boppana S, et al. Saliva polymerase-chain-reaction assay for cytomegalovirus screening in newborns. N Engl J Med 2011; 364: 2111-2118. AVailable online at http://www.nejm.org/doi/full/10.1056/NEJMoa1006561 through http://www.nejm.org. Accessed June 2011. 

Weintrub, Peggy Sue MD. PCR Saliva Testing for Congenital Cytomegalovirus Infection Shows Promise. June 1, 2011.  Pediatrics and Adolescent Medicine. Available online at http://pediatrics.jwatch.org/cgi/content/full/2011/601/2?q=etoc_jwid through http://pediatrics.jwatch.org. Accessed June 2011.