Comparison of a Latex Agglutination Test and Four Culture Methods for Identification of Group A Streptococci in a Pediatric Office Laboratory

A latex agglutination test and four culture methods for the detection of group A hemolytic streptococci were compared in a pediatric office laboratory. The anaerobic (GasPak) and Detekta-Kit methods produced the highest recovery rates, but aerobic incubation of 5% blood agar plates gave very acceptable results (sensitivity 92%, or 98% if the 1+ positive cultures were eliminated; specificity 100%), and had fewer disadvantages. Delaying inoculation of plates for 2 to 6 hours resulted in significantly greater numbers of strongly positive (3+ and 4+) cultures. The group A selective sheep blood agar media as used in this study offered no advantage. The Culturette test had a sensitivity of 72% and specificity of 98%, compared with the GasPak method, and 77% and 97%, respectively, compared with standard aerobic cultures. Thus it appears too insensitive to be used alone, but might complement culture methods in selected patients.