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Multicenter Evaluation of the Cepheid Xpert GBS LB XC Test
Phyu M Thwe1,2, Matthew L Faron3, David T Pride4,5
1Department of Pathology, University of Texas Medical Branch, Galveston, Texas, USA.
Insights
A new molecular test accurately detects Group B Streptococcus (GBS) in pregnant women, improving early sepsis diagnosis. This advancement offers reliable screening for Streptococcus agalactiae, reducing newborn mortality and morbidity risks.
Area of Science:
- Microbiology
- Molecular Diagnostics
- Neonatal Health
Background:
- Neonatal sepsis from Streptococcus agalactiae (GBS) is a major cause of infant mortality.
- Current guidelines recommend universal GBS screening in pregnant women with intrapartum antibiotic prophylaxis.
- Rapid molecular tests are used, but some have shown false negatives due to gene deletions.
Purpose of the Study:
- To evaluate the performance of the new Xpert GBS LB XC molecular test for GBS detection.
- To assess the test's accuracy using nutrient broth-enriched rectal/vaginal samples from antepartum women.
- To compare the new test against established diagnostic methods.
Main Methods:
- A multicenter study prospectively enrolled 621 antepartum samples.
- Samples were tested using the Xpert GBS LB XC assay.
- Performance was compared to a composite method (Hologic Panther Fusion GBS + culture + MALDI-TOF MS) and bacterial culture + MALDI-TOF MS.
Main Results:
- The Xpert GBS LB XC test demonstrated high sensitivity (99.3%) and specificity (98.7%) versus the composite method.
- Compared to bacterial culture, sensitivity was 99.1% and specificity was 91.8%.
- The test showed comparable performance to the composite method and equivalence to traditional culture.
Conclusions:
- The Xpert GBS LB XC test is a reliable and accurate method for GBS screening in pregnant women.
- This molecular assay addresses limitations of previous tests, reducing false negatives.
- The findings support the use of this test for improved GBS detection and management.
Abstract:
Early-onset neonatal sepsis due to Streptococcus agalactiae (group B Streptococcus [GBS]) infection is one of the leading causes of newborn mortality and morbidity. The latest guidelines published in 2019 recommended universal screening of GBS colonization among all pregnant women and intrapartum antibiotic prophylaxis for positive GBS. The updated procedures allow rapid molecular-based GBS screening using nutrient broth-enriched rectovaginal samples. Commercially available molecular assays for GBS diagnosis target mainly the cfb gene, which encodes a hemolysin protein responsible for producing the Christie-Atkins-Munch-Petersen (CAMP) factor. cfb is considered a conserved gene in essentially all GBS isolates. However, false-negative GBS results on Cepheid Xpert GBS and GBS LB tests due to deletions in or near the region that encodes cfb were reported recently. Therefore, the new Xpert GBS LB XC test was developed. This study is a multicenter evaluation of the new test for GBS identification from nutrient broth-enriched rectal/vaginal samples from antepartum women. A total of 621 samples were prospectively enrolled. The samples were tested with the Xpert GBS LB XC test, the composite comparator method, which included the Hologic Panther Fusion GBS test combined with bacterial culture, followed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) identification, and bacterial culture alone, followed by MALDI-TOF MS identification. The respective sensitivity and specificity of the Xpert GBS LB XC test were 99.3% and 98.7% compared to the composite comparator method and 99.1% and 91.8% compared to bacterial culture alone with MALDI-TOF MS identification. Overall, the Xpert GBS LB XC test performed comparatively to the composite comparator method and is equivalent to traditional bacterial culture followed by MALDI-TOF MS.
