Rapid antigen testing for group A Streptococcus by DNA probe

The Gen-probe group A Streptococcus direct test (GASD), a nucleic acid probe assay for detecting GAS from throat swabs, has recently been developed. The test uses an acridium ester-labeled DNA probe which is complementary to the rRNA of Streptococcus pyogenes. In this study, 318 single culturette throat swabs were tested by this method using culture as a "gold standard." After plating onto trypticase soy agar plates with 5% sheep blood, swabs were stored at 4 degrees C for no more than 72 h before the probe assay was performed. Our patient population consisted of symptomatic outpatients seen in the Memorial Hospital Emergency Department and in the Family Care Center. After discrepancy testing, sensitivity, specificity, and positive and negative predictive values were 91.4%, 97%, 91.4%, and 97%. The GASD is a rapid, easy-to-perform method for batch screening for streptococcal pharyngitis.