COMPARISON OF BIOSTAR STREP-A OIA OPTICAL IMMUNE ASSAY, ABBOTT TESTPACK PLUS STREP-A, AND CULTURE WITH SELECTIVE MEDIA FOR DIAGNOSIS OF GROUP-A STREPTOCOCCAL PHARYNGITIS

We directly compared three techniques for the diagnosis of group A str eptococcal pharyngitis in 500 symptomatic children seen in the Emergen cy Department or Child Care Clinic of The Children's Hospital of Denve r. Throats were vigorously swabbed with two rayon swabs, which were tr ansported immediately to the Microbiology Laboratory. Each swab was cu ltured aerobically on Strep A Isolation Agar (Remel) and then tested f or antigen-one swab by the Strep A OIA optical immune assay (BioStar) and the other by the TestPack Plus Strep A (Abbott) technique. Each te st was performed blind to the others. The refrigerated pledget was cul tured in Todd-Hewitt broth if an antigen test was positive and both di rect plate cultures were negative (the ''gold standard'' was any cultu re positive). All isolates were serologically grouped. Of 500 complete patient cultures, 151 (30%) were positive for group A streptococcal g rowth. The two antigen tests gave comparable results with an average s ensitivity of 83%. Each was significantly (P < 0.02) less sensitive th an its corresponding culture. The BioStar Strep A OIA optical immune a ssay produced significantly(P < 0.003) more false-positive results tha n did the Abbott test. Rapid antigen testing is not sensitive enough t o eliminate the need for backup cultures.