A COMPARISON OF THE YIELD OF POSITIVE ANTENATAL GROUP-B STREPTOCOCCUSCULTURES WITH DIRECT INOCULATION IN SELECTIVE GROWTH-MEDIUM VERSUS PRIMARY INOCULATION IN TRANSPORT MEDIUM FOLLOWED BY DELAYED INOCULATION IN SELECTIVE GROWTH-MEDIUM

OBJECTIVE: Our purpose was to compare the yield of positive group B St reptococcus cultures with standard medium for transport of culture swa bs compared with use of selective medium during transport. STUDY DESIG N: Cultures of introitus, perineum, and rectum were obtained on prenat al patients; one was placed in standard transport medium, and the othe r directly in selective growth medium. Swabs in standard transport med ium were plated for routine culture and then transferred to selective growth medium, Todd-Hewitt broth, in the laboratory. RESULTS: A total of 307 of 1222 (25.1%) patients had a positive result by any method. W ith direct inoculation into selective growth medium at the time of sam pling, 4.6% of positive cultures were missed. With delayed inoculation into selective growth medium, 16.3% were missed (p < 0.001). Without use of selective media (routine culture), 31.9% were missed (p < 0.001 ). CONCLUSIONS: Use of standard transport medium with subsequent trans fer into selective growth medium results in a significantly decreased yield of positive group B Streptococcus cultures.