EVALUATION OF 2 RAPID TESTS FOR DETECTION OF MATERNAL ENDOCERVICAL GROUP-B STREPTOCOCCUS - ENZYME-LINKED-IMMUNOSORBENT-ASSAY AND GRAM STAIN

Objective: To establish the reliability of two rapid tests for detecti on of group B streptococcus, the new enzyme-linked immunosorbent assay (ELISA) and the Gram stain. In addition, we wished to determine wheth er the combination of these tests would increase test sensitivity. Met hods: During a 2-year period, cervical secretions from 660 patients wh o presented with either premature rupture of membranes or preterm labo r at a gestational age of 37 weeks or less were tested by three method s: the Equate ELISA test, a Gram stain smear, and a culture for group B streptococcus. Results of the rapid tests were compared with the cor responding culture results. Results: Cultures were positive for group B streptococcus in 50 patients, a prevalence of 7.5%. The sensitivity for the Equate ELISA test was 24% and for the Gram stain, 20%. Specifi city was 95 and 89%, respectively. When results of these tests were co mbined, the sensitivity increased to 26%. Both rapid tests yielded a h igh rate of false positives. In more than 50% of false-positive cases, bacteria other than group B streptococcus were isolated. Conclusion: Neither the Gram stain nor the Equate ELISA test is sensitive enough t o be used as a screening test for the identification of group B strept ococcus. Furthermore, the combination of both rapid tests yielded only a slight increase in sensitivity. The high false-positive rate of the ELISA test seems to be related to a cross-reactivity of the anti-grou p B streptococcal antibody with other cervical bacteria.