The presence of free infectious cytomegalovirus (CMV) in the plasma of donated CMV-seropositive blood and platelets.

An in vitro study was carried out to determine the presence of free infectious CMV in the supernatant of donated units of blood and platelets which were known to be CMV seropositive. One sample was taken from each of 10 units of CMV-seropositive platelet donations which were 4 days old. Ten units of seropositive blood were sampled at intervals over their storage lifespan. Each sample was divided into two and thrombin was added to one of them. The samples were all prepared by centrifugation. The resulting supernatant from the clotted samples was used in in vitro culture studies using the MRC-5 cell line to ascertain the infectivity of the samples. The anticoagulated supernatants were subjected to PCR analysis to detect the presence of free genomic CMV DNA. All of the units of blood and platelets tested positive for the presence of genomic CMV DNA by PCR. Seven out of the 10 units of blood were culture positive from samples taken 3-4 weeks into their shelf-life. None of the platelet samples was culture positive. The cultures of supernatants taken from seropositive blood were negative when the units were fresh, but further into their storage life, the cultures became positive, indicating that infectious material was released into the supernatant during storage, presumably due to the breakdown of intact white cells.