Rapid antigen detection in the diagnosis of group A streptococcal pyoderma: influence of a "learning curve effect" on sensitivity and specificity.

To evaluate the efficacy of rapid antigen detection for diagnosis of Group A streptococcal pyoderma, lesions on 129 children were swabbed for culture and for rapid antigen detection testing. Duplicate cultures and duplicate rapid antigen tests were performed in two laboratories. The sensitivity and the specificity of the test were high, supporting the validity of this technique in diagnosing streptococcal pyoderma. Of importance, however, was the documentation of a learning curve effect on the sensitivity and specificity. There was a significant difference between the early samples and the later samples in one laboratory which had less previous experience with the rapid antigen detection test. By the time the later samples were collected, the proficiency of the first laboratory was equal to that of the second laboratory for both sensitivity and specificity. Although a learning curve effect on sensitivity and specificity of rapid antigen detection tests for Group A streptococci has been suspected, this is the first documentation of such an effect. This finding has important clinical implications for using rapid antigen detection tests for Group A streptococcal infections.