Abstract
BackgroundStreptococcus Group B (GBS) colonization in pregnant women is the most important risk factor for newborn disease due to vertical transmission during delivery. GBS colonization during pregnancy has been implicated as a leading cause of perinatal infections. Traditionally, pregnant women are screened for GBS between 35 and 37 weeks of gestation. However, antenatal culture-based screening yields no information on GBS colonization status and offers low predictive value for GBS colonization at delivery. Numerous assays have been evaluated for GBS screening in an attempt to validate a fast and efficient method. The aim of this study was to compare bacteria isolation by culture and two qPCR techniques, targeting sip and cfb genes, respectively, for detecting colonizing GBS.MethodsCultures – the gold-standard technique, a previous qPCR technique targeting the sip gene, and a new proposed qPCR assay targeting the cfb gene were evaluated as diagnostic tools on 320 samples.ResultsConsidering cultures as the gold standard, the evaluated qPCR method detected 75 out of 78 samples, representing a sensitivity of 93.58% (95% confidence interval (CI), 90.89–96.27) and specificity of 94.62% (95% CI, 91.78–97.46). However, an additional analysis was performed for true positives that included not only samples showing positives by culture but samples showing positive for both qPCR assays. The sensitivity and specificity were recalculated including these discrepant samples and a total of 89 samples were considered as positive, giving a prevalence of 27.81%. With this new analysis, the qPCR targeting the cfb gene showed a sensitivity of 95.5% (95% CI, 88.65–98.59) and specificity of 99.13% (95% CI, 96.69–99.97).ConclusionsThe new qPCR method is a sensitive and specific assay for detecting GBS colonization and represents a valuable tool for identifying candidates for intrapartum antibiotic prophylaxis. Cultures should be retained as the reference and the routine technique because of its specificity and cost analysis ratio, but it would be convenient to introduce PCR techniques to check negative culture samples or when an urgent detection is required to reduce risk of infection among infants.
Highlights
Streptococcus Group B (GBS) colonization in pregnant women is the most important risk factor for newborn disease due to vertical transmission during delivery
Bacterial isolation by culture was considered the gold standard for Group B Streptococcus (GBS) diagnosis (100% specificity is assumed) [17, 20]
Among the 78 samples indicated positive by culture, 75 and 73 samples were positive by PCR targeting the sip gene (PCR-A) and PCR targeting the cfb gene (PCR-B), respectively
Summary
Streptococcus Group B (GBS) colonization in pregnant women is the most important risk factor for newborn disease due to vertical transmission during delivery. Vertical transmission to the newborn occurs during labor via fetal aspiration of infected amniotic fluid or during passage through the birth canal [4]. Due to this vertical transmission, GBS infection is the a important cause of neonatal morbidity and mortality in the United States [5, 6]. Determination of infection at the time of delivery is essential for neonatal vertical transmission prevention [7], because some women are intermittent carriers of GBS and the rate of GBS colonization may vary during pregnancy [8]. The use of antibiotic prophylaxis on the basis of risk assessment leads to unnecessary treatment in many women [11]
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