A COMPARATIVE-EVALUATION OF 3 METHODS OF ANTIVIRAL SUSCEPTIBILITY TESTING OF CLINICAL HERPES-SIMPLEX VIRUS ISOLATES

Background: Current methods of antiviral susceptibility testing for herpes simplex virus (HSV) are poorly standardized and have rarely been compared critically. Objectives: To compare the three most commonly utilized HSV susceptibility assays for accuracy of result, method of implementation, and time required. Study design: We compared susceptibility results for acyclovir and foscarnet using the plaque reduction, dye uptake and DNA hybridization assays in 30 patient isolates of HSV, of varying susceptibility pattern. Compared parameters included: values for ID50 (the concentration of drug required to inhibit virus growth by 50% or more), ratio of ID90 to ID50, and correlation of susceptibility result with clinical response to antiviral therapy, when available. In addition, we compared ease of the assay, presence of objective endpoint, time required to generate the susceptibility result, and necessary equipment for implementation. Results: The dye uptake yielded ID50 results that were approximately two-fold greater than those from the plaque reduction assay, while ID50 values from the DNA hybridization assay were one-half those from the plaque reduction assay. Comparison of the correlation of susceptibility result with clinical response to acyclovir therapy in 17 instances and to foscarnet therapy in 10 instances suggested the possibility of a somewhat greater discriminative ability of the dye uptake assay, and a somewhat lesser discriminative ability of the DNA hybridization assay, when compared with results from the plaque reduction assay in isolates with borderline acyclovir susceptibility. Conclusions: Larger comparative studies are necessary to further differences in discriminative ability of the three assays for HSV. All three assays were deemed suboptimal due to an overly long turnaround time, associated expense, and/or level of equipment required for their performance. Continued evaluation of alternative, more rapid assays is therefore warranted.