The effect of dexamethasone on the detection of cytomegalovirus in tissue culture and by immunofluorescence.

With the development of both monoclonal antibodies to the immediate early nuclear antigen (EA) of cytomegalovirus (CMV) and different methods used for its detection, the time required for diagnosis of infection has become significantly shorter. However, discrepancies between tissue culture (TC) and the EA assay methods have raised questions concerning which method is more sensitive and whether a positive test result truly represents infection or latency. We have found that dexamethasone (Dex), when incorporated into the growth medium at a concentration of 10(-5) M, decreases the variability between the two techniques and increases the sensitivities of both TC and EA assay. However, for Dex to be effective, it was necessary to prepare, seed and grow the indicator cells in the presence of 10(-5) M Dex. Additionally, the cells had to be in contact with Dex for approximately 24 h before any effect was observed. Except for this step, all other procedures were the same as have been described elsewhere. In this study, four methods were compared: TC, TC with Dex (TC-D), EA, and EA with Dex (EA-D). Of 251 clinical specimens (200 microliter/well), 46 (18%) were positive for CMV. Of the 46, 30 (65%) were positive by TC, 39 (85%) by TC-D, 39 (85%) by EA, and 42 (91%) by EA-D. Without Dex the combination of TC plus EA detected only 41 of 46 (84%) positive samples. In contrast, the presence of Dex allowed detection of all 46 positive samples by TC-D and EA-D. Also, more fluorescent forming units (FFU) were detected by EA-D than EA (mean 14.8 FFU), and cytopathic effect was detected sooner (mean 9 days) by TC-D than by TC. Dex significantly increased the detection of CMV by TC (P less than 0.05). In addition, the use of any one of these methods alone did not effectively detect all positive samples. We suggest the combination of TC-D and EA-D for detection of all samples positive for CMV and to detect other viruses that may be missed by the EA method.