Poster Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

Use of Dried Blood Spot Samples for Quantification of Group B Streptococcus Alpha-like Surface Protein Antibodies (#310)

May Murra 1 2 3 , Tom Hall 4 , Jens K Moeller 1 3 , Mohammad RC Khalil 1 5 , Tine B Henriksen 6 7 , Hans Christian Slotved 8 , Stine Y Nielsen 3 9
  1. Department of Regional Health Research, University of Southern Denmark , Vejle, Denmark
  2. Department of Clinical Microbiology, Vejle Hospital, Vejle, Denmark
  3. Department of Clinical Microbiology, Vejle Hospital, Vejle, Denmark
  4. Centre for Neonatal and Paediatric Infection, Institute for Infection and Immunity, St George's, University of London, London, UK
  5. Department of Obstetrics, Kolding Hospital, Kolding, Denmark
  6. Department of Pediatrics and Adolescent Medicine, Aarhus University Hospital, Aarhus, Denmark
  7. Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
  8. Department of Bacteria, Parasites, and Fungi, Statens Serum Institut, Copenhagen, Denmark
  9. Department of Biomedicine, Aarhus University, Aarhus, Denmark

Background
Dried blood spot samples(DBSS) are routinely collected from neonates for diagnostic purposes. 

Most countries store DBSS at room-temperature. However, the Danish National Biobank store DBSS at -20°C. This provides a unique opportunity for serological studies on Group B Streptococcus(GBS). 

The GBS-NN/NN2-vaccine targets four immunogenic alpha-like surface proteins(AlpNs) - Rib, AlpC, Alp1 and Alp2/3 - expressed in >99% of invasive GBS-isolates.

This study aimed to assess the feasibility of AlpN-IgG-quantification in DBSS.

 

Methods
Pregnant women(35-37 weeks) were included at Kolding Hospital, Denmark(June 2023-March 2024).

Umbilical cord blood(UC) was collected after birth, followed by DBSS and baby heel blood(BH) from the neonate at age 2-3 days.

A total of 32 DBSS, 28 BH, and 28 UC samples was collected.

Concentration of each AlpN-IgG(ng/ml) was measured by ELISA at MinervaX Laboratory, Lund, Sweden.

Concordance Correlation Coefficient(CCC) was used to assess agreement of precision and accuracy of AlpN-IgG in DBSS vs. serum.

A DBSS-to-serum conversion factor(CF) was applied by Deming Regression analysis if necessary.  

 

Results
For all four AlpN-IgG concentrations, the agreement between DBSS and BH was strong/perfect(CCC=0.84-0.96). 

The agreement between AlpN-IgG in DBSS vs UC was high-moderate/perfect(CCC=0.79-0.95).

The agreement between UC and BH was perfect(CCC≥0.94).

CF was then applied to achieve perfect agreement for some AlpNs and comparisons.

 

Conclusion
Quantification of AlpN-IgG in DBSS is precise and accurate when compared to serum samples(BH/UC).

DBSS are well-suited for a large-scale serological study of AlpN-IgG in GBS cases vs. controls.