Additional Study Information: This research study for people who have tested positive for cytomegalovirus (CMV) after receiving a solid-organ transplant or stem cell transplant. This is a non-interventional study. This study involves the use of an investigational test called the Aptima CMV Quantification Diagnostic Assay (Aptima CMV Quant Assay) to determine the levels of CMV in your body. This test has not been approved for sale or use by the US Food and Drug Administration (FDA). Its use is experimental in this study. Hologic, Inc. sponsors this research study. In addition to the standard of care routine CMV monitoring, a study blood sample will be taken by the study team and processed for plasma (pale yellow liquid part of blood). The plasma sample will be tested to determine the levels of CMV in your body. After the testing is completed, the remaining plasma sample and information collected with the samples may be stored for future research with your permission. This study will use your CMV plasma sample.