DETECTION OF GROUP-B STREPTOCOCCUS BY IMMUNOASSAY FOLLOWING ENRICHMENT IN LIM-SELECTIVE BROTH MEDIUM

Rapid immunoassays have been developed to decrease the time to detecti on of Group B Streptococcus (GBS) carriage in pregnant women. In this study, a total of 162 pregnant women, considered to be high-risk obste tric patients, were seen in the Family Care Center at Memorial Hospita l of Rhode Island, a 300-bed teaching hospital associated with Brown U niversity Medical School. Vaginal and rectal specimens were taken and tested for GBS by using two vapid enzyme immunoassays (EIAs) that were compared with culture. Quidel and Hybritech ICON Group B strep tests were run following 4 h incubation in the selective enrichment LIM Grou p B strep broth; cultures were done both directly and after enrichment . Results with bath EIAs were identical, with overall sensitivity, spe cificity, and positive and negative predictive values of 38%, 98%, 88% , and 84% respectively. However, when women having positive cultures w ere separated into moderately to heavily colonized (greater than or eq ual to 3 + ) and lightly colonized (less than or equal to 2 + ) popula tions, the sensitivities were 82% and 19%, respectively. Although GBS assays are useful in the rapid diagnosis of heavily colonized women, c ulture following enrichment remains the most sensitive method for a li ghtly colonized population.