Quantitative analysis of cytomegalovirus load using a real-time PCR assay

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Abstract
A novel real-time PCR assay system was developed to quantify the cytomegalovirus (CMV) genome load. The real-time PCR assay could detect from 6 to over 10(6) copies of CMV-DNA with a wide linear range. The virus load of immunocompromised patients with symptomatic CMV infections was quantified and compared to that of asymptomatic ones. In symptomatic patients, all 17 peripheral blood leukocytes were positive for CMV DNA, and its mean value was 10(3.3) copies/10(6) cells. On the other hand, only 9 of 38 samples (24%) were positive in the asymptomatic patients, and its mean titer was lower (10(2.0) copies/10(6) cells) than that of the symptomatic group (P = 0.002). In plasma, the virus genome was detected in 13 out of 17 samples from symptomatic patients (76%), and its mean value was 10(4.0) copies/ml. In contrast, for the asymptomatic group, only one out of 36 samples were positive (3%). Finally, this system was used to monitor two patients with CMV infections serially. The CMV DNA copy number changed with their clinical symptoms and anti-CMV therapy, and virtually paralleled the result of the pp65 antigenemia assay in both cases. In one patient with the cord blood transplantation, however, the CMV DNA became positive faster than the antigenemia assay. These results indicate that this assay is sensitive and useful for estimating the CMV genome load not only in peripheral blood leukocytes but also in plasma. It can be very helpful for diagnosing CMV-related diseases and monitoring the virus load in patients with CMV infections.