DIAGNOSTIC-SIGNIFICANCE AND CLINICAL IMPACT OF QUANTITATIVE ASSAYS FOR DIAGNOSIS OF HUMAN CYTOMEGALOVIRUS INFECTION DISEASE IN IMMUNOCOMPROMISED PATIENTS/

In recent years several assays have been developed for quantitation of human cytomegalovirus (HCMV) in blood of immunocompromised (transplan ted and AIDS) patients. It is currently agreed that the only reliable indication of the degree of dissemination of HCMV infection/disease is the measurement of HCMV in blood. Diagnosis of HCMV end-organ disease (organ localizations) often does not benefit from quantitation of vir us in blood, but requires detection and quantification of virus in sam ples taken locally. The most important and clinically useful diagnosti c assays for HCMV quantitation in blood are: i) viremia, quantifying i nfectious HCMV carried by peripheral blood leukocytes (PBL); ii) pp65- antigenemia, quantifying the number of PBL positive for HCMV pp65 in t he nucleus; iii) circulating cytomegalic endothelial cell (CEC) viremi a (CEC-viremia) measuring the number of circulating CEC carrying infec tious HCMV (during the antigenemia assay); iv) leuko- and plasma-DNAem ia, quantifying the number of HCMV genome equivalents present in PBL o r plasma, respectively, by quantitative polymerase chain reaction (Q-P CR). Other less widely used assays are: i) determination of immediate early and late gene trancripts (mRNA) to detect active viral infection ; ii) in situ hybridization to detect viral nucleic acid (DNA or RNA) in tissue sections or cell smears; iii) in situ PCR to detect a low DN A copy number in single cells. Monitoring of HCMV infection/disease in transplant recipients and AIDS patients has established threshold val ues for different assays above which HCMV-related clinical symptoms ar e likely to appear. These values are approximately 10 for viremia, 100 for antigenemia and 1,000 CE for leukoDNAemia, and are valid for both solid organ and bone marrow transplant recipients as well as AIDS pat ients, whereas presence of even a single circulating CEC is sufficient to suggest the presence of a disseminated HCMV infection with potenti al organ involvement. Monitoring of antiviral treatment of HCMV infect ion/disease with either ganciclovir or foscarnet has aimed at keeping virologic parameters below the threshold values reported above. On the other hand, rising levels of the same virologic parameters during ant iviral treatment have mostly revealed emergence of resistant HCMV stra ins to either ganciclovir (mutations in the UL97 or DNA polymerase gen e) or foscarnet (mutations in the UL54 gene) or both drugs (double res istance with both types of mutations). Rapid assays for chemosensitivi ty testing of virus directly in clinical specimens have been developed to allow timely (4-6 days) detection of resistance to a drug and prov ide clinicians with the rationale for shifting to an alternative treat ment.