To the Editor.
—In the article by Dr Gerber and colleagues1 reporting an office-based multicenter investigation of the optical immunoassay (OIA) test for group A β-hemolytic streptococcal (GABHS) pharyngitis, the authors concluded that "with adequately trained personnel, negative OIA test results may not always need to be routinely confirmed with blood agar plate (BAP) cultures." We believe the authors' conclusions are based less on the quality of the testing personnel or the performance specifications of the OIA and more on the quality of the BAP culture procedure used in the study.Presumptive differentiation of GABHS and non—group A streptococci may be accomplished by the bacitracin test, in which a zone of inhibition is noted on a pure subculture of β-hemolytic colonies. Bacitracin disks placed on primary cultures on nonselective media, as was done in this study, may detect as little as 54% of group A streptococci.2 We compared
Dale JC, Wollan P, Cockerill FR. Use of Optical Immunoassay to Diagnose Streptococcal Pharyngitis. JAMA. 1997;278(1):23. doi:10.1001/jama.1997.03550010037028