SENSITIVITY OF INTRAPARTUM GROUP-B STREPTOCOCCAL SCREENING AND IN-VITRO COMPARISON OF 4 RAPID ANTIGEN TESTS

Objectives: To evaluate the sensitivity of intrapartum screening for g roup B streptococcal (GBS) colonization and to compare 4 rapid GBS ant igen tests in vitro. Design: Two swabs of the lower vagina of 769 part urients were taken; one swab was cultured, the other was frozen at -70 degrees C until antigen testing with the Group B Strep Test (Quidel) of the culture positive samples was performed. The Quidel test was the n compared with 3 other rapid GBS antigen tests in vitro: Wellcogen St rep B (Wellcome Diagnostics), Slider meningite Strepto B (bioMerieux) and ICON Strep B (Hybritech). The supernatant of 29 GBS cultures in To dd-Hewitt broth was tested in bacterial concentrations of 10(6), 10(7) , and 10(8) Colony-Forming Units (CFU)/ml, respectively. Results: Lowe r vagina GBS carrier rate was 13.4% (103/769) and heavy colonization ( growth density 3 and 4 on blood agar plates) was found in 5.2% (40/769 ). The Group B Strep Test detected 11% (11/103) of GBS carriers, with a sensitivity for heavy colonization of 25% (10/40). In vitro none of the tests scored positively with a concentration of 106 CFU/ml, while with 10(7) CFU/ml the enzyme immunoassay tests (Quidel, Hybritech) wer e more sensitive (McNemar test, P < 0.05) than the latex agglutination tests (Wellcome Diagnostics, bioMerieux). Conclusions: Although in vi tro the enzyme immunoassay tests are more sensitive than the latex agg lutination tests, sensitivity in vivo is too low to recommend the use of rapid antigen tests for general screening.