Comparison of cytomegalovirus antigenemia assay with shell vial-indirect immunofluorescence assay for rapid detection of cytomegalovirus in blood

The recent article by Mazzulli et al. (4) further demonstrates the increasing interest of virologists and microbiologists in the cytomegalovirus antigenemia (CMV-Ag) assay. Mazzulli and coworkers report that the CMV-Ag assay is more sensitive than the shell vial-indirect immunofluorescence assay (SVAIFA), perhaps implying that the direct antigen detection assay should be considered the method of choice for the rapid detection of CMV in peripheral blood. Most clinical virologists and microbiologists, however, would agree that the SVA-IFA remains the most commonly used methodology in the general diagnostic virology laboratory for 1(or 2-) day detection of the infectious agent in blood. Presented data which support the CMV-Ag assay having improved sensitivity over the SVA-IFA must be carefully scrutinized, as such information will have a major impact on the test system used in diagnostic laboratories involved with samples from patients suspected of a treatable CMV infection. The CMV-Ag assay and the SVA-IFA have recently been compared in our laboratory (3). Among 186 peripheral blood specimens collected from our immunocompromised patients, we found no significant difference between the detection rate of CMV in blood (2 x 10' polymorphonuclear leukocytes [PMNLs]) by the CMV-Ag assay and that by the SVA-IFA. Perhaps we are misreading Mazzulli and coworkers' methods, but several points in their execution of the SVA-IFA might need to be clarified. First, was parallel testing performed on blood specimens when the CMV-Ag assay was compared with the SVA-IFA? Specifically, the CMV-Ag assay was noted to have used PMNLs (8). Were PMNLs used solely in assessing the performance of the SVA-IFA, or were shell vials inoculated with leukocyte populations consisting of PMNLs plus monocytes and macrophages? Additionally, was the number of cells used in the preparation of slides for the CMV-Ag assay equal to that total number inoculated into shell vials? Lastly, Mazzulli et al. centrifuged their shell vials for 40 min at temperatures ranging from 20 to 30°C . In our laboratory, shell vials are routinely centrifuged for 60 min at a temperature of 36 ± 1°C (2, 3). We cannot help but question whether the centrifugation period at the relatively low temperatures of 20 to 30°C might have adversely affected virus penetration and resulted in suboptimal yields of the CMV immediate-early and early nuclear antigens. CMV penetration of host cell fibroblasts and the recovery of virus from centrifuged and noncentrifuged assay systems are acknowledged to occur optimally at temperatures slightly above the mid-30°C range (1, 5-7). The study by Mazzulli et al. is an important contribution. Their investigation adds credence to the applicability of the CMV-Ag assay as a sensitive and simple to perform methodology for same-day detection of CMV in the blood. However, additional parallel studies comparing this assay with the SVAIFA are needed before the medical community may accept the suggested superiority of the CMV-Ag assay, except where patients on CMV antiviral drugs are concerned.