2005 Volume 115 Issue 12 Pages 1797-1803
In order to test the effectiveness of rapid immunoassay kits for the detection of group A streptococcal antigen, we compared the positive rates using these kits with those using a culture method for testing throat swab specimens from 103 patients with suspected group A streptococcal infections (scarlet fever). The kits showed 95.7% and 89.3% for sensitivity and specificity, respectively. All 47 samples of S. pyogenes cultured were sensitive to all of the 16 antibiotics that we tested. The positive rates were lower in patients who had begun treatment with antibiotics 2～3 days before testing and remarkably lower in patients receiving antibiotics for more than 4 days before testing. Based upon these findings, we conclude that the rapid diagnostic immunoassay kits for early detection of group A streptococcal antigen are effective. However, we should take into account the influence of prior antibiotic treatment, the possible presence of bacteria with antigens in common with group A streptococcal antigen, and the quality of the throat swab specimens.