A rapid method for detection of group B streptococcal colonization

Abstract

Vertical transmission of group B streptococci, the most frequent cause of early neonatal sepsis, can be interrupted by intrapartum antibiotics. However, rapid methods for detecting colonized women must be developed to limit the administration of antibiotics to those who are at risk of delivering an infected infant. The accuracy of a colorimetric test using starch serum medium on vaginal and rectal specimens from women with preterm labor or prolonged rupture of membranes was evaluated. The test was interpreted by labor and delivery room nurses without special microbiologic training. Starch serum medium results were compared with those obtained from routine cultures. Thirteen of 29 positive vaginal cultures (45%) and eight of 18 positive rectal swabs (44%) were identified by nurses using the rapid method. This was significantly different (P less than .001) from sensitivities of 93 and 95%, respectively, for the same vaginal and rectal specimens interpreted by a bacteriology technologist. The specificity for the test from both sites was 95% for the nurses. The sensitivity was 53 and 36% for vaginal and rectal swabs, respectively, for a subgroup of mothers whose infants were assessed as clinically septic. The low sensitivity of starch serum medium as interpreted by nurses in the labor suite is inadequate to allow the test to replace cultures in identifying women colonized with group B streptococci. Efforts to increase the sensitivity should be directed toward improving nursing staff interpretation rather than improving the medium itself.