Time, cost, and efficacy study of identifying group A streptococci with commercially available reagents.

During the 12-month period primary throat, wound, and skin cultures, tentatively identified as B streptococci, were submitted by 10 different clinical laboratories for evaluation. A total of 692 beta-hemolytic streptococci were isolated from cultures submitted and examined in parallel by the fluorescent-antibody, precipitin, and bacitracin techniques. An evaluation of the specificity and sensitivity in conjunction with basic and personnel costs was determined for each method. The standard Lancefield precipitin method was established as the standard by which the bacitracin and flourescent antibody techniques were compared. With some variation depending on the commerical source of the disc, approximately 7% of the strains examined produced false reactions with the bacitracin disc. False-negative reactions were rarely noted by the group A fluorescent antibody technique (0.5%), but an appreciable number of other Lancefield groups (B, C, and G) were nonreactive with homologous conjugates.