[Simple and reliable detection of beta-hemolytic streptococci in throat swabs with the streptococcus-isocult].

Culture of throats specimens is essential in the diagnosis of streptococcal tonsillo-pharyngitis. Selective sheep's blood agar media for beta-hemolytic streptococci have been developed to simplify throat streptococcal bacteriology. In this prospective study the reliability and practical performance of a selective medium of this kind, the Isocult culture test for throat streptococci, were evaluated in 226 pediatric patients with the clinical diagnosis of acute tonsillo-pharyngitis. At the time of diagnosis two throat specimens were obtained from each patient; one swab was cultured for group A beta-hemolytic streptococci on standard laboratory media, and the other on the Isocult media. Procedure and interpretation of the two culture methods were carried out independently. In 209 (92.5%) of the 226 patients the two culture results were in agreement, i.e. either positive (19 patients) or negative (190 patients) for group A beta-hemolytic streptococci. In comparison to routine bacteriology the Isocult results showed sensitivity, specificity, and predictive value of 86%, 93% and 91%. Neither the performance nor the interpretation of the Isocult method require special bacteriological training or equipment. It is concluded that the Isocult culture test for throat streptococci is a simple and reliable diagnostic tool in the management of patients with sore throat.