Enhancement of varicella-zoster virus detection in A-549 shell vials by use of freeze-thawed specimens, extended incubation, and "a centrifuged, not incubated" direct detection method.

A total of 95 clinical samples were cultured for periods of 2 and 7 days in centrifuged A-549 shell vials before and after freezing and thawing of specimens. In addition, centrifuged A-549 shell vials were tested directly for varicella-zoster virus without incubation using a direct fluorescent antibody (DFA) technique. Twenty-seven specimens were positive by at least one method. The sensitivity for DFA on unincubated A-549 shell vials was 85.2%; for unfrozen 2-day cultures, 88.9%; for unfrozen 7-day cultures, 92.6%; for freeze-thaw 2-day cultures, 92.6%; and for freeze-thaw 7-day cultures, 96.3%. Freeze-thawed specimens cultured for 7 days yielded the highest number of positive results with conspicuous cell-to-cell spread as a sign of viral replication.