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Research shows best methods for serotyping pneumococci in carriage studies

Research News
Wednesday, November 18, 2015 - 9:00am
New global research led by Murdoch Children's Research Institute has identified the best method for detecting carriage of pneumococci, bacteria that cause pneumonia and other serious infections, especially in children. This analysis could inform pneumococcal vaccine evaluation and development and thereby help stop the spread of this deadly bacteria.

Pneumococci are extremely diverse bacteria with over 90 different types (serotypes) that cause a wide variety of diseases. Pneumococcal pneumonia is a leading cause of death among young children and kills over half a million young children every year, with most deaths occurring in low income countries. Disease is preceded by carriage of the bacteria in the nose and throat of healthy children. This carriage also helps in the spread the bacteria among people. Adding to the complexity, some children carry multiple serotypes at the same time.

Current childhood pneumococcal vaccines protect against a subset of 10 to 13 of the over 90 different strains. The vaccines can protect against both carriage and disease. Identification of pneumococcal serotypes found in carriage is a key element of assessing the impact of these pneumococcal vaccines.

The traditional serotyping method used to identify pneumococcal types is expensive, slow, and difficult to perform. Several laboratories have developed new serotyping methods, but their performance has not been evaluated in a rigorous way. The aim of the PneuCarriage project, funded by the Bill & Melinda Gates Foundation, was to identify the best methods for serotyping pneumococci in carriage studies, which are used in many countries to evaluate pneumococcal vaccines. In this large, international project led by Dr Catherine Satzke and Professor Kim Mulholland from the Institute, researchers evaluated 20 different serotyping methods for their ability to correctly identify pneumococcal types.

Initially, reference sample sets were distributed to 15 research groups for blinded testing. The five top performing methods were then used to test 260 nasal samples collected from young children in six high-burden countries. A molecular method in which bacteria were cultured and then examined on a DNA microarray was the top-performing method. A latex sweep method, which uses antibodies to detect different pneumococcal types, also performed well.

As part of a follow up project also funded by the Bill & Melinda Gates Foundation, the DNA microarray method and the latex sweep method have been established at Murdoch Children's and in collaborating laboratories in South Africa.

Results from this comprehensive evaluation will inform future vaccine evaluation and impact studies, particularly in low-income settings, where pneumococcal disease burden remains high. This study has been published in the open access journal PLOS Medicine and the full article can be found here.

This project bought together field sites from Asia and Africa, along with 15 leading pneumococcal research groups around the world.

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