Comparison of a Rapid Test versus Culture for Detecting Group B Streptococcus Colonization in Late Pregnancy

This study aims to compare the diagnostic performance of colloidal gold immunochromatographic assay (GICA) with culture-based screening for antepartum detection of Group B Streptococcus (GBS).

This prospective study was conducted in a tertiary hospital in South China, performing GBS screening on women at 35-37 weeks of gestation. GICA and direct bacterial culture were separately performed on paired rectovaginal swabs. Decisions about intrapartum antibiotic prophylaxis (IAP) were based on the GBS positive results by either GICA or culture.

The detection rate for GBS colonization was 7.5% (31/414) by the culture and 16.4% (68/414) by the GICA, with significant difference (p<0.001). Kappa value between the two methods was 0.516 (p<0.001), suggesting moderate concordance. Against the reference standard of direct culture, the GICA showed a sensitivity of 90.3%, specificity of 89.6%, positive predictive value (PPV) of 41.2%, negative predictive value (NPV) of 99.1%, and accuracy of 89.6%. Among individuals with positive GICA, the culture-positive group was associated with significantly higher proportion of IAP and lower relative risk of adverse pregnancy outcomes compared to the negative group.

The GICA demonstrates 90% sensitivity and specificity in detecting maternal GBS colonization compared to culture. This rapid test may be considered as a promising alternative, particularly for emergency labor and large-scale screening in resource-limited settings. However, the clinical overuse of IAP should be concerned.