Rapid detection of group B streptococcal carriage in parturient women using a modified starch serum medium.

Group B streptococcal disease is the most frequent infectious cause of morbidity and mortality of newborns in North America. There is evidence that vertical transmission, the major route of neonatal acquisition, may be interrupted by administration of antibiotics during the intrapartum period. A modified starch serum medium has been developed that will allow the rapid identification of group B streptococci, by observation of a color change, in vaginal and rectal swabs. This medium was compared to a "gold standard" of routine culture. The sensitivity and specificity of the test were found to be 100% and 99%, respectively, in 237 specimens from women attending different clinics who submitted vaginal swabs. All color changes occurred within 6 hours. Vaginal and rectal carriage of the organism were found in 8% and 12%, respectively, of women in preterm labor. In this population the sensitivity and specificity of the test for vaginal specimens were 97% and 98%, respectively. The corresponding values for rectal swabs were 94% and 100%. The test can potentially select carrier mothers who could benefit the most from intrapartum antibiotics. This medium may also be used for transport to enhance detection of colonization.