Cytomegalovirus detection

Keywords: Cytomegalovirus nucleic acid amplification, CMV PCR

Specimen:

Anticoagulated blood (EDTA, ACD preferable for some test methods) 10mL, CSF, urine, tissue, throat washes, bronchoalveolar lavages.

In general, specimens must be processed within 4-2 h of collection. This varies with the test method in use - consult laboratory.

Method:

Quantitative results may also be obtained using the branched-DNA signal amplification assay or the hybrid capture CMV DNA assay.

Other methods include:

Viral culture including spin-amplification shell vial assay with IF.

Immunostaining or nucleic acid probe detection of CMV early antigens (all specimen types).

Nucleic acid probe following amplification (all specimen types).

Immunostaining or IF on slide preparations of polymorphonuclear leucocytes (blood), also known as the pp65 antigenaemia assay.

Both nucleic acid probe after PCR amplification and the pp65 antigenaemia assay can be used for quantitation.

Application:

Diagnosis of congenital CMV infection and diagnosis of some of the less common forms of CMV infection eg, CMV encephalitis.

Quantitation of the systemic CMV load (blood) is useful in identifying the subset of immunocompromised patients infected with CMV who are at risk of progressing to disease, allowing 'pre-emptive' therapy.

Interpretation:

Detection of CMV in urine, throat washings or other body fluids within the first 2 weeks of life is the most sensitive and specific means of confirming the diagnosis of congenital infection. Urine is the preferred specimen and culture is usually sufficiently sensitive for this purpose.

Sensitive techniques for the detection of CMV in blood (pp65 antigenaemia assay, or NAA detction) detect CMV in almost all patients with CMV disease and a negative result excludes the diagnosis. However, CMV is also detected in a substantial number of patients with asymptomatic infection who never progress to disease.

Quantitation of CMV requires individual interpretation because of the lack of well-established standard levels and the different rates of progression of the infection to overt disease from the time of first detection in different illness (eg, rapid in bone marrow transplant patients, less rapid in patients with HIV-AIDS).

The most consistent marker of progression is a rising viral load in an individual patient, rather than an absolute value.

Reference:

Boeckh M and Boivin G. Clin Microbiol Rev 1998; 11: 533-554.