Evaluation of new Granada medium (modified) for the antenatal screening of group B streptococcus.

New Granada medium (NGM), modified by the substitution of trimethoprim for methotrexate, was compared to a selective Todd-Hewitt broth (NPC broth) and direct plating onto Edwards medium for assessment of genital carriage of group B streptococcus in pregnant women. Whilst NGM was found to be less sensitive (85%) than NPC broth (95%) and more sensitive than Edwards medium (67%), its use reduced the direct laboratory cost of screening by approximately 41% and also improved the time to report a result by 24 hrs.