Comparative quantification of human cytomegalovirus DNA in blood of immunocompromised patients by PCR and Murex Hybrid Capture™ System

Background: Monitoring of human cytomegalovirus (HCMV) load by quantification of antigenemia, viremia and DNAemia is helpful in the management of HCMV infections in immunocompromised patients. In fact, threshold values of these viral parameters are associated with the emergence of clinical symptoms. In addition, the response to antiviral treatment is revealed by a decrease in viral load or virus disappearance from blood.

Objectives: Aim of this study was to compare HCMV DNA quantification in blood of immunocompromised patients by an `in house' developed quantitative PCR (Q-PCR) assay and the commercially available Murex Hybrid Capture™ System (HCS).

Study design: HCMV DNA was quantified in 95 blood samples from 12 heart and heart-lung transplant recipients and 27 AIDS patients using both techniques. For HCS analysis 3.5 ml whole blood were utilized, whereas Q-PCR was performed using 1×10⁵ peripheral blood leukocytes (PBL). HCMV DNA levels obtained by HCS and Q-PCR were expressed as number of genome equivalents (GE)/ml whole blood or 1×10⁵ PBL, respectively. Results from HCS and Q-PCR were compared and submitted to statistical analysis. In addition, HCMV DNA values were compared to levels of antigenemia and viremia.

Results and Conclusions: Sensitivity of HCS, antigenemia and viremia with respect to Q-PCR were 37.2, 79.5 and 33.3%, respectively. Specificity was 100% for all techniques. On average, samples positive by Q-PCR only, contained low amounts of HCMV DNA. In particular, 45 (91.8%) out of 49 samples negative by HCS and positive by Q-PCR showed <500 GE/1×10⁵ PBL. A significant correlation was found between quantitative DNA levels in samples positive by both HCS and Q-PCR (n=29, R=0.693, P<0.01). HCS positivity was associated to significantly higher DNA values as determined by Q-PCR as well as to significantly higher antigenemia and viremia levels. A decrease in DNAemia levels was observed using both HCS and Q-PCR after antiviral treatment. Given that the great majority of blood samples missed by HCS contain low levels of HCMV DNA which are not clinically significant, HCS seems very promising as an alternative to HCMV DNA quantification by PCR in solid organ transplant recipients and AIDS patients.