Antigen Detection Test for Group a Beta-Hemolytic Streptococcal Pharyngitis that is Sufficiently Sensitive for Use without Confirmatory Cultures

Abstract

An ADT for the rapid diagnosis of GABHS pharyngitis that uses optical immunoassay (OIA) technology has recently been developed and marketed (Strep A OIA, BioStar Inc., Boulder, CO). It has been claimed that the OIA is more sensitive than the blood agar plate (BAP) culture and that negative OIA test results do not require confirmation with a BAP culture¹. The purpose of this study was to compare the accuracy of the OIA as performed and interpreted in office practice settings with the accuracy of the BAP culture as performed and interpreted under similar conditions. Because neither the BAP culture nor the OIA test has a sensitivity or specificity of 100%, a “gold standard” had to be established against which the accuracy of each of these tests could be determined. The “gold standard” against which the sensitivity and specificity of both the BAP culture and OIA (as performed and interpreted in the office) were determined was a combination of BAP culture with serologic confirmation of GABHS and Todd-Hewitt broth (THB)-enhanced culture as performed and interpreted in either of two streptococcal research laboratories.