Accuracy of rapid antigen detection test for group B streptococci in the indigenous vaginal bacterial flora

Objective: To test the sensitivity of the rapid group B streptococci (CBS) antigen test ICONR and compare its accuracy in women with vaginal enterococ ci or with non-specific disturbance of the lactobacillary flora. Study desi gn: The ICONR, aerobic culture and a microscopic wet mount evaluation were done on a vaginal sample in 254 unselected women presenting for routine gyn ecologic care in an academic hospital in Flanders, Belgium and tested by Ch i(2) [diagnostic odds ratio (DOR) and its 95 percent confidence limits]. Re sults: Sensitivity of the test was 70%, specificity 99.5%. Prevalence of GB S was 10.6% overall, 23% in the group with abnormal vaginal flora and 7% in the normal group (p=0.002). Accuracy of the ICONR was not affected by abno rmal vaginal flora, but was significantly lower in the presence of enteroco cci: the DOR decreased from 490 to 58, and the positive predictive value fr om 94 to 80%. Conclusion: With a sensitivity of 70% the enzyme immunoassay ICONR does not appear to be suitable as a practical screening tool for dete cting GBS carriage in normal or preterm laboring women. In the presence of enterococci the test performed less well, with a DOR falling by 8 to 9 fold . We presume this is due to lower specificity in vivo in the presence of en terococci, as non-specific disturbance of the lactobacillary nora did not i nterfere with test results.