Using Dried Blood Spots for a Sero-Surveillance Study of Maternally Derived Antibody against Group B Streptococcus

Abstract

Vaccination during pregnancy could protect women and their infants from invasive Group B Streptococcus (GBS) disease. To understand if neonatal dried blood spots (DBS) can be used to determine the amount of maternally derived antibody that protects infants against invasive GBS disease, a retrospective case-control study was conducted in England between 1 April 2014 and 30 April 2015. The DBS of cases with invasive GBS disease (n = 61) were matched with healthy controls (n = 125). The haematocrit, DBS storage temperature, freeze-thaw cycle, and paired serum/DBS studies were set up to optimise the antibody assessment. The samples were analysed using a multiplex immunoassay, and the results were assessed using parametric and nonparametric tests. Antibody concentrations were stable at haematocrits of up to 50% but declined at 75%. DBS storage at room temperature was stable for three months compared with storage from collection at −20 °C and rapidly degraded thereafter. Total IgG levels measured in DBS and paired serum showed a good correlation (r2 = 0.99). However, due to suboptimal storage conditions, no difference was found in the GBS IgG levels between DBS samples from cases and controls. We have demonstrated a proof of concept that assays utilising DBS for assessing GBS serotype-specific antibodies in infants is viable. This method could be used to facilitate future large sero-correlate studies, but DBS samples must be stored at −20 °C for long term preservation of antibody.

Development of A Standardized Opsonophagocytosis Killing Assay for Group B Streptococcus and Assessment in an Interlaboratory Study

“…It is important to note that the assay is highly sensitive with 50% killing observed at very low concentrations of anti-CPS IgG (1.65-3.70 ng/mL depending on serotype). This sensitivity will allow quantification of OPKA activity in samples with low antibody concentrations, such as those from natural immunity studies, which may include dried blood spot samples [25] that are diluted 10-fold during elution from the matrix before analysis.…”