ADT's for GABHS pharyngitis generally are highly specific but insufficiently sensitive. Therefore, a sheep blood agar (SBA) culture has been recommended as backup to confirm negative ADT results. An ADT for the rapid diagnosis of GABHS pharyngitis (Strep A OIA) that utilizes a new technology, optical immunoassay (OIA), was recently introduced and alleged to be more sensitive than SBA cultures. We investigated patients with acute pharyngitis seen at three pediatric offices in Connecticut and at three pediatric offices in Chicago to compare the accuracy of the OIA as performed and interpreted in a practice setting with the accuracy of the SBA culture as performed and interpreted under similar conditions. We used a combination of the central laboratory's interpretation of the SBA culture and a Todd Hewitt broth culture of the transport tube pledget as the “gold standard.” Among 983 patients enrolled in Connecticut, the sensitivities of the OIA and SBA culture compared with the “gold standard” were 94% and 89%, respectively(p<.01), while the specificities were 96% and 99%, respectively (p<.01). Among 1,130 patients enrolled in Chicago, the sensitivities of the OIA and SBA culture were 78% and 72%, respectively (p<.01), while the specificities were 88% and 98%, respectively (p<.01). While our intent was to have identical “gold standards” for Connecticut and Chicago, the“gold standard” in Chicago resulted in considerably more positive cultures for GABHS than in Connecticut; this difference accounts for the relatively low sensitivities of both the OIA and SBA cultures in Chicago. More important than the absolute values of the sensitivities is that the OIA was more sensitive than the SBA culture in all six pediatric offices.

The results of this comprehensive study suggest that: 1) the sensitivity of the OIA test is at least equivalent to that of routine SBA culture when both are performed and interpreted in an office setting, 2) the specificity of the OIA test is comparable to that reported for other ADT's, and 3) negative OIA test results need not be confirmed with backup SBA cultures. [Funded by BioStar, Inc.]