Comparison of throat culture methods for the recovery of group A streptococci in a pediatric office setting

Abstract

Objective: To compare a single-plate method for the recovery of group A streptococci with other methods that have recently been reported as being significantly more sensitive.

Design: Throat swabs were allowed to dry for 2 to 6 hours before inoculating 5% sheep blood agar plates. Stabs were made into the agar, bacitracin disks were placed on the primary plates, and the cultures were incubated aerobically. Using duplicate throat swabs, the recovery rates of the above method were compared with the following ones: a carbon dioxide-enhanced incubation atmosphere, an anaerobic atmosphere with a selective blood agar medium, and a Todd-Hewitt broth medium.

Setting: A five-pediatrician office.

Patients: A total of 301 pediatric patients with pharyngitis were evaluated using all comparative methods. In addition, duplicate swabs from 590 pediatric patients were compared with each other using the same single-plate method.

Results: There were no significant differences between any of the methods. The sensitivity of the single-plate method compared with selective plates incubated anaerobically was 96%.

Conclusions: In a pediatric office setting, a single-plate method using aerobic incubation was adequately sensitive for the recovery of group A beta-hemolytic streptococci. Transport medium, selective medium, carbon dioxide enhancement, and anaerobic incubation did not significantly improve recovery. The present federal regulations that restrict the use of nonselective media and bacitracin disks on primary plates should be reevaluated.