Optimisation of prenatal group B streptococcal screening

The purpose of the study presented here was to confirm the high yield of group B streptococci (GBS) on Granada medium for the detection of pregnant GBS carriers and to compare the results with those obtained using standard Columbia blood agar at two participating centers in Belgium. Culture results of the vaginorectal swabs obtained at the two centers were also compared. A total of 1,142 samples (838 in Leuven and 304 in Bonheiden) obtained from consecutive pregnant women were cultured onto both media. Of all GBS carriers 84.7% were detected on Columbia blood agar and 93.4% on Granada agar (P<0.01, McNemar test). The addition of Granada agar was responsible for a 15% higher rate of detection of GBS carriers. As a result of this study, both participating hospitals will use a combination of Granada agar with Columbia blood agar for optimal GBS screening in the future.