Evaluation of a new rapid antigen detection kit for group A beta-hemolytic streptococci

To evaluate the use of a new rapid antigen-detection kit for group A beta-hemolytic streptococcus and compare results with previously published studies.

Throat swabs were obtained prospectively from patients, aged one to 18 years, presenting to the emergency department, acute concerns clinic, and walk-in clinic of an urban tertiary care children's hospital. Throat swabs were first inoculated on a 5% sheep blood agar plate and then used for the streptococcus A optical immunoassay (OIA) kit. Results of both the throat culture and the rapid antigen-detection test were then compared.

Two-hundred thirty-three patients were enrolled. Seventy-three patients had a positive culture and 63 patients had a positive OIA. Fifteen patients had a false negative result for the OIA kit and five patients had a false positive result. Test sensitivity was 79.5%, specificity was 96.9%, positive predictive value was 92.1%, and negative predictive value was 91.2%

Although previous studies have demonstrated OIA kit sensitivities as high as 98.9% and authors have, as a result, recommended that the performance of a backup throat culture for a negative OIA test is unnecessary, our results do not support this. A sensitivity of 79.5% is not sufficiently high to justify omission of a standard throat culture. Accordingly, all OIA tests that are negative should be confirmed by the performance of a throat culture.