Prospective comparison of R-mix shell vial system with direct antigen tests and conventional cell culture for respiratory virus detection.

BACKGROUND AND OBJECTIVES: Conventional cell culture (CC) has limited clinical utility as a result of the extended incubation period often required for virus isolation. Alternative methodologies have been introduced in an effort to improve turnaround times. One such system, the R-mix shell vial is discussed herein. The study objectives were: (a) to establish R-mix testing parameters as compared to direct antigen testing (DAT) and CC, and (b) to assess technical aspects and cost of R-mix in a high volume clinical virology laboratory. STUDY DESIGN: A prospective analysis of respiratory samples submitted to the clinical virology laboratory between November 2004 and April 2005 was performed. All specimens were inoculated onto R-mix shell vials (SV) and CC tubes; and a subset also underwent DAT for influenza A and B and/or RSV. A retrospective estimated cost analysis was made. RESULTS: A total of 563 samples were included in the study, which collectively revealed a total of 207 viruses. Sensitivity of R-mix for seven major respiratory viruses ranged from 45% to 83% compared to CC and DAT, while mean time to detection (TTD) varied from 1.1 to 1.4 days. In addition to these viruses, 23 picornaviruses, 11 CMV isolates and 5 HSV isolates were detected by CC alone. CONCLUSIONS: The R-mix system has similar sensitivity as CC for the detection of parainfluenza 1-3 and influenza A/B while dramatically reducing the TTD. Furthermore, it is significantly more sensitive and produces more timely results for RSV than CC; yet, neither method offers a diagnostic benefit over rapid DAT for RSV detection. The sensitivity of R-mix for adenovirus appears to be significantly lower than that of CC. Lastly, methodologies other than R-mix must remain in place under circumstances where identification of other potential viral respiratory pathogens, including herpesviruses and picornaviruses, is desired.