Real-time polymerase chain reaction for the rapid detection of group B streptococcal colonization in neonates

Abstract

Background: Group B streptococcal (GBS) infection remains a leading cause of neonatal sepsis. Currently, the management guidelines of neonates born to women with unknown GBS status at delivery are unclear. In this cohort, who undergo at least a 48-hour observation, a rapid method of detection of GBS colonization would allow targeted evaluation and treatment, as well as prevent delayed discharge.

Objective: The goal of this research was to evaluate the validity of rapid fluorescent real-time polymerase chain reaction in comparison with standard culture to detect GBS colonization in infants born to women whose GBS status is unknown at delivery.

Design/methods: Neonates at >32 weeks' gestation born to women whose GBS status was unknown at delivery were included. Samples were obtained from the ear, nose, rectum, and gastric aspirate for immediate culture and real-time polymerase chain reaction after DNA extraction using the LightCycler. Melting point curves were generated, and confirmatory agar gel electrophoresis was performed.

Results: The study population (n = 94) had a mean +/- SD gestational age of 38 +/- 2 weeks and birth weight of 3002 +/- 548 g. The rates of GBS colonization by culture were 17% and 51% by real-time polymerase chain reaction. The 4 surface sites had comparable rates of GBS. The overall sensitivities, specificities, and positive and negative predictive values of real-time polymerase chain reaction were: 90%, 80.3%, 28%, and 98.9%.

Conclusions: Real-time polymerase chain reaction resulted in a threefold higher rate of detection of GBS colonization and had an excellent negative predictive value in a cohort of neonates with unknown maternal GBS status at delivery. Thus, real-time polymerase chain reaction would be a useful clinical tool in the management of those infants potentially at risk for invasive GBS infection and would allow earlier discharge for those found to be not at risk.

FIGURE 1

A photograph of the confirmatory 2% agar gel electrophoresis showing the target 153 bp product.

FIGURE 2

Melting curves (A and C plot the fluorescence and temperature; B and D show the first negative derivative of fluorescence and temperature) where all samples were negative for GBS (A and B), samples from the nose and gastric aspirate were positive, and those from ear and rectum were negative (C and D).