Rapid detection of group B streptococcal colonization of the genital tract by a commercial optical immunoassay

Abstract

The performance of a commercial optical immunoassay (OIA) was compared at two institutions with that of routine agar and broth culture methods for the detection of group B streptococcal (GBS) colonization of the genital tract. The Strep B OIA (Bio Star, USA) was used to test 962 vaginal swabs from pregnant women for the presence of GBS antigen. The prevalence of GBS vaginal colonization in this population was 22.4%. The OIA results were compared with those of culture on trypticase soy agar with 5% sheep blood (TSA) and broth enhanced culture (Lim broth). Sensitivity and specificity values of the OIA method compared to TSA culture alone were 82.5% and 91.8%, respectively. The sensitivity of the OIA method was equivalent to that of TSA culture (62.4% vs. 64.4%; p> 0.5, chi 2 = 0.01) when the data were compared with broth culture. The extent of colonization affected the sensitivity of the OIA method: 100% of 4+, 94% of 3+, 96% of 2+, and 63% of 1+ TSA plates were detected by the OIA test. The commercial OIA method demonstrated sensitivity equivalent to that of TSA culture for the detection of GBS colonization. The OIA test offers two additional advantages over culture: reduced time required to obtain results (30 min vs. days) and the ability to detect GBS antigen in samples with compromised viability. The results of this study suggest that the Strep B OIA test can be a useful diagnostic tool in the management of early-onset GBS disease.

Infections in International Pregnancy Study: Performance of the Optical Immunoassay Test for Detection of Group B Streptococcus

“…The specificity was uniformly high, 85 to 98%, similar to the 98.4% in our study. Conversely, previously reported test sensitivities varied widely but were generally higher (37 to 81%) (2,5,7,(12)(13)(14)(17)(18)(19) than the value we found (26.8%). The most important reason for this variability may be the extent to which the subjects were colonized.…”

“…The most important reason for this variability may be the extent to which the subjects were colonized. The sensitivity of the OIA has been higher (61 to 100%) when compared with third-and fourth-quadrant positive blood agar cultures (2,5,7,(12)(13)(14). Our finding was within this range (68.4%).…”

“…Detection of heavy colonization has traditionally relied on culture methods, which may not be feasible in some health care settings and require 1 to 3 days before results are available. Unfortunately, most rapid GBS tests have poor sensitivity (7,13). The Strep B optical immunoassay (OIA; ThermoBiostar, Inc., Louisville, Colo.) is a rapid method which may have higher sensitivity for dense GBS colonization (14).…”

Group B Streptococcus: Prevention of Early-Onset Neonatal Sepsis

“…When compared with the standard method, it has sensitivity between 47% and 63% with specificity between 86% and 96% (44)(45)(46). Although the rapidity of results is useful, the sensitivity and specificity of this test limit applicability.…”

Variations in the investigation and management of group B streptococcus in Scotland

“…Up to 40% of pregnant women are carriers of group B streptococcus (GBS), (Anthony et al, 1981;Allardice et al, 1982;Thomsen et al, 1987;Regan et al, 1992;Carroll et al, 1996) and up to 3% develop GBS disease (Ostroff and Steaffens, 1995). Around half of their offspring are symptomatic at birth, and 20% die from the disease (Dillon et al, 1987;Ostroff, 1995).…”