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

Background: Current methods of antiviral susceptibility testing for he rpes simplex virus (HSV) are poorly standardized and have rarely been compared critically. Objectives: To compare the three most commonly ut ilized HSV susceptibility assays for accuracy of result, method of imp lementation, and time required. Study design: We compared susceptibili ty 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 b y 50% or more), ratio of ID90 to ID50, and correlation of susceptibili ty result with clinical response to antiviral therapy, when available. In addition, we compared ease of the assay, presence of objective end point, time required to generate the susceptibility result, and necess ary 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 a ssay were one-half those from the plaque reduction assay. Comparison o f the correlation of susceptibility result with clinical response to a cyclovir therapy in 17 instances and to foscarnet therapy in 10 instan ces suggested the possibility of a somewhat greater discriminative abi lity of the dye uptake assay, and a somewhat lesser discriminative abi lity of the DNA hybridization assay, when compared with results from t he plaque reduction assay in isolates with borderline acyclovir suscep tibility. Conclusions: Larger comparative studies are necessary to fur ther differences in discriminative ability of the three assays for HSV . All three assays were deemed suboptimal due to an overly long turnar ound time, associated expense, and/or level of equipment required for their performance. Continued evaluation of alternative, more rapid ass ays is therefore warranted.