Group B Streptococcus (GBS) can be found colonizing about 25% of all healthy, adult women and is the leading infectious cause of early neonatal morbidity and mortality in the United States. The rate of early-onset neonatal infection is ~0.22 cases per 1,000 live births (2016) and can cause sepsis resulting in neurologic sequelae such as sight/hearing loss and cerebral palsy. The CDC recommends that vaginal/rectal swabs be collected between 35 to 37 weeks gestation to test the mother for carriage and prophylactic measures taken for colonized women.
This study was undertaken to evaluate the clinical performance of the WASPLab® Artificial Intelligence/Interpretative Algorithm (PhenoMATRIX™[PM] Copan Diagnostics) in detection of GBS from LIM broth enriched cultures plated on CHROMID® Strepto B (ChromGBS) Chromogenic Media (bioMérieux) after 24 and 48 hours of incubation. The performance of the PhenoMATRIX was compared to manual culture review of the digital images and molecular detection of GBS (BD MAX, BD Diagnostics Systems). Discrepant results were adjudicated using a second molecular method (Cepheid GeneXpert GBS, Cepheid, Inc.).
A total of 486 vaginal/rectal swab samples were collected for the study. Specimens were determined to be positive if they had a positive molecular result and/or a confirmed GBS culture result. Thus, the overall detection of GBS was considered to be 94/486 (19.3%). The ChromGBS plus PM algorithm detected 88/94 (93.6%) GBS samples at 24 hours demonstrating a sensitivity and specificity of 93.6% and 79.9%, respectively. Increasing the incubation time to 48 hours increased GBS detection to 90/94 (95.7%) for a sensitivity of the ChromGBS plus PM of 95.7%, but specificity of 66.6%. Molecular detection of GBS resulted in 90/94 (95.7%) positive samples for an overall sensitivity of 95.74% with a specificity of 98.8%. Technologist read of ChromGBS without PM, detected 84/94 (89.4%) of positive GBS colonies by 48 hours for a sensitivity and specificity of 89.4% and 99.5%, respectively.
The use of ChromGBS in combination with the PM AI/IA System was equivalent to the sensitivity of molecular detection. Further, the algorithm never called a culture negative that was determined to be positive by manual reading and identified an additional six true positive specimens that were missed by manual digital image culture reading.
