Pharyngeal carriage of group B streptococci: detection by three methods.

The prevalence of pharyngeal carriage of group B streptococci was evaluated in patients with and without the complaint of a sore throat by three methods (blood agar plates, Columbia CNA agar plates, and a selective enrichment broth containing gentamicin and nalidixic acid). The overall carriage rate of group B streptococci was 12%, and there was no significant difference between the two groups of patients. The selective broth medium was more sensitive than the two solid agar plate methods in detecting carriage, and 37% of all group B streptococci were recovered solely from the broth. Use of the broth alone would have permitted a 94% detection of the group B streptococcal carriers.