Cytomegalovirus (CMV) infection, a frequent complication affecting solid organ and hematopoietic stem cell transplant recipients, is commonly diagnosed and monitored by quantitative PCR (qPCR) methods. Viral load (VL) is used as a correlate for disease severity and progression. The objective of this study was two-fold: 1) assess CMV qPCR positivity rate and VL of de-identified patient samples by specimen type; and 2) compare the performance of the two CMV qPCR assays comprising the qPCR method used for clinical testing by a reference laboratory. A total of 36,525 samples submitted by physicians during a portion of 2016 were analyzed by CMV qPCR. Specimen types tested (in order of prevalence) included plasma, CSF, urine, bronchoalveolar lavage (BAL), fecal, serum, tissue, bone marrow, amniotic fluid, aqueous fluid and vitreous fluid. Of these specimen types, plasma represented the majority (67.6%) of samples tested, followed by CSF, urine and BAL (each approx. 7% of samples tested). The positivity rates were highest in vitreous fluid, serum, plasma and bone marrow, with each exceeding 20% positive samples. The positivity rate was lowest in CSF and amniotic fluid (2.1% and 4.0%, respectively). Median VL values were highest in amniotic fluid, aqueous fluid, vitreous fluid and urine (6.89, 6.23, 5.37, and 4.67 log₁₀ IU/mL, respectively) and lowest in plasma and serum (2.85 and 2.78 log₁₀ IU/mL, respectively). The two CMV qPCR assays comprising the qPCR method detected a region of glycoprotein B (gB) and DNA polymerase (DNA pol) CMV genes, and 3,864 de-identified 2016 results were analyzed. Linear regression analysis of samples with both results >LOQ (N = 323 or 8.4% of samples) demonstrated strong correlation (slope = 0.9919 (95% CI 0.9726 to 1.011), r2 = 0.9694) although DNA pol values were on average 0.28 log₁₀ IU/mL higher (linear regression y-intercept = -0.2497). A total of 66 samples had DNA pol results >LOQ while gB results from the same samples were <LOQ. Only five samples had gB results >LOQ with DNA pol results <LOQ. A total of 189 gB negative samples were positive by DNA pol, while 25 DNA pol negative samples by were positive by gB. In conclusion, CMV positivity rates and VL varied widely by specimen type. Use of two CMV gene targets in a qPCR method improved both the quantitative ability (number of results >LOQ) and sensitivity (fewer negative results) of CMV detection.

CITATION INFORMATION: Kleiboeker S. Cytomegalovirus Viral Load: Characterization of Results from Clinical Specimens. Am J Transplant. 2017;17 (suppl 3).

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