New rapid test for Group B strep shows promise

A new rapid test for Group B Streptococcus (GBS) provides reliable results in hours, compared with traditional culture that takes days, according to a report by investigators at the 33rd annual Society of Maternal-Fetal Medicine meeting, held in February.

Published in Infectious Diseases in Obstetrics and Gynecology, the findings showed that antepartum GBS colonization was identified in 6.5 hours with a novel immunoblot-based assay using an antibody-coated nitrocellulose membrane. The test had a high level of validity and demonstrated substantial agreement among observers. Traditional cultures for GBS take about 48 hours. 

Between March 2011 and May 2012, researchers from the University of Texas Health Science Center, Baylor College of Medicine, and Kelsey-Seybold Clinic enrolled 356 women in a study of GBS screening at 35 to 37 weeks’ gestation. The mean age of the women enrolled in the study, each of whom had 3 vaginal-rectal swabs, was 26.8, ±0.6 years. Two swabs were processed with traditional culture (commercial vs in-house laboratory) whereas the third was processed with the rapid assay using the immunoblot-based test.

The researchers compared the sensitivity, specificity, positive predictive value, and negative predictive value with 95% confidence intervals for the commercial laboratory GBS culture and the initial accelerated GBS test result. The time from initiation of the GBS accelerated test until a result was available was 6.5 hours. The number of observed agreements between the 2 blinded-independent readers was 314 (88.2%), which was significantly higher than the number of results expected to be in agreement (178 [50%]).

“In our evaluation,” the researchers conclude, “the accelerated GBS test was found to perform well for the detection of GBS in antepartum patients, was easy to use, and had the unique potential for applying antibiotic resistance testing during the culture step. These characteristics may allow for the implementation of this test across a wide range of clinical scenarios in geographical settings where access to specialized equipment is limited.”

Faro JP, Bishop K, Riddle G, et al. Accuracy of an accelerated, culture-based assay for detection of Group B Streptococcus. Infectious Diseases in Obstetrics and Gynecology. 2013;article ID 367935. doi:10.1155/2013/367935.