• Robert D Sheeler, Margaret S Houston, Sharon Radke, Jane C Dale, and Steven C Adamson.
• Department of Family Medicine, Mayo Clinic, Rochester, MN 55905, USA.
• J Am Board Fam Pract. 2002 Jul 1;15(4):261-5.

BackgroundSome clinicians have questioned the accuracy of rapid diagnosis of group A streptococcal pharyngitis by commercial immunochemical antigen test kits in the setting of recent streptococcal pharyngitis, believing that the false-positive rate was increased because of presumed antigen persistence.MethodsWe studied 443 patients--211 cases--who had clinical pharyngitis diagnosed as group A beta-hemolytic streptococcus infection in the past 28 days and compared them with 232 control patients who had symptoms of pharyngitis but no recent diagnosis of streptococcal pharyngitis. Our aim was narrowly focused to compare the rapid strep test with the culture method we used in our clinical practice.ResultsWe found that the rapid strep test in this setting showed no difference in specificity (0.96 vs 0.98); hence, the assertion that rapid antigen testing had higher false-positive rates in those with recent infection was not confirmed. We also found that in patients who had recent streptococcal pharyngitis, the rapid strep test appears to be more reliable (0.91 vs 0.70, P < .001) than in those patients who had not had recent streptococcal pharyngitis.ConclusionsThe findings of this study indicate that the rapid strep test is both sensitive and specific in the setting of recent group A beta-hemolytic streptococcal pharyngitis, and its use might allow earlier treatment in this subgroup of patients.

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