If a CMV infection becomes dangerous, antiviral agents can be used to moderate the impact. Many of these compounds are toxic, so the physician must know the severity of the infection--a measure known as viral load (number of virus copies per microliter of blood)--to prescribe the optimal dosage and duration of treatment.

The current means of measuring viral load is to use polymerase chain reaction (PCR) to amplify a region of the CMV gene and then use a calibration curve to estimate the number of virus particles in the original sample. Accuracy of these measurements can vary greatly from one test facility to another, as there are many different PCR protocols used to determine viral load, including commercial and "in-house" laboratory assays.

The new [US] National Institute of Standards and Technology (NIST; Gaithersburg, MD, USA) reference, SRM 2366, provides a standardized CMV DNA. Consistency of the viral DNA in the standard was ensured by manufacturing it in Escherichia coli bacteria. These E. coli cells each contain a copy of the CMV genome in a "DNA construct"--an artificially constructed segment of nucleic acid that codes for a specific product, in this case, CMV DNA. The DNA copies made by this E. coli cell culture can then be purified and quantified using digital polymerase chain reaction (PCR).

SRM 2366 consists of three solutions, each with a specific concentration of CMV DNA copies per microliter: 420, 1,702, and 19,641. These are designed to qualify prepared calibration samples. They also can be used as quality control samples for diagnostic equipment. For added traceability, the SRM certificate of analysis includes the genetic sequences of the nine CMV genome regions copied for the standard.

CMV is found in 50% to 80 % of the population. CMV generally remains latent in an infected person unless certain conditions trigger its activation. CMV poses a significant health risk to people who are immunocompromised and babies who receive the virus from their mothers before birth. Congenital CMV infections cause more long-term problems and childhood deaths than many other prenatal disorders including fetal alcohol syndrome, Down syndrome, and neural tube defects such as spina bifida.

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National Institute of Standards and Technology