621 Bacteria Strains Cause Pneumonia Around the World

PCV13 vaccines prevent Streptococcus pneumoniae which is the most common cause of bacterial pneumonia

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Pneumococcal conjugate vaccines (PCVs) have been focused on the 13 pneumococcal serotypes that account for most of the diseases in infants. 

And vaccines such as Prevnar13 have substantially reduced the global burden of invasive pneumococcal disease. 

Pneumococcal infections can range from ear and sinus infections to pneumonia and bloodstream infections. Children younger than 2 years old and adults 65 years or older are among those most at risk for disease, says the Centers for Disease Control and Prevention.

Despite the success of PCVs, the invasive pneumococcal disease remains an important health priority owing to an increase in the incidence of disease caused by non-vaccine serotypes.

This event is known as ‘serotype replacement.’

Serotype replacement has been reported by several countries, but not the USA. 

According to a new study published in The Lancet on June 10, 2019, various studies characterizing serotype replacement in cases of the invasive pneumococcal disease have primarily focused on changes in serotypes. 

Two mechanisms of serotype replacement have been suggested.

The first is the expansion of non-vaccine-type lineages to partly fill the niche vacated by vaccine-type lineages. 

The second is a within-lineage expansion of non-vaccine serotypes, which can be explained as a concomitant increase in non-vaccine serotypes and decrease in vaccine serotypes within a lineage after PCV introduction, usually through the expansion of existing non-vaccine-type components rather than contemporaneous capsular switching. 

Multiple serotypes (vaccine and non-vaccine) expressed by a single pneumococcal lineage were not unusual because pneumococci are able to replace capsular biosynthesis genes through the acquisition of foreign DNA by natural genetic transformation. 

The Global Pneumococcal Sequencing (GPS) project was set up to guide the design of preventive measures for pneumococcal diseases beyond PCV13 by defining pneumococcal lineages across a global pneumococcal population and attempting to capture how lineages evade vaccines. 

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As part of the GPS project, a high-resolution population structure of 621 Global Pneumococcal Sequence Clusters (GPSCs) was defined by analyzing 20,027 pneumococci genomes.

In this study, the researchers aimed to identify the predominant serotypes causing invasive pneumococcal disease among children younger than 3 years and their associated lineages after the introduction of PCV13 in six countries, investigate the mechanisms of serotype replacement in disease, and identify international lineages contributing to post-PCV13 invasive pneumococcal disease and report their antibiotic-resistant traits. 

This study found 5 most prevalent serotypes in the PCV13 period varied between countries, with only serotypes 5, 12F, 15B/C, 19A, 33F, and 35B/D common to 2 or more countries. 

These serotypes were associated with more than 1 lineage, except for serotype 5 (GPSC8). 

Serotype replacement was mainly mediated by the expansion of non-vaccine serotypes within vaccine-type GPSCs and, to a lesser extent, by increases in non-vaccine-type GPSCs. 

A globally spreading lineage, GPSC3, expressing invasive serotypes 8 in South Africa and 33F in the USA and Israel, was the most common lineage causing non-vaccine serotype invasive pneumococcal disease in the PCV13 period. 

We observed that same prevalent non-vaccine serotypes could be associated with distinctive lineages in different countries, which exhibited dissimilar antibiotic resistance profiles. 

In total, these scientists discovered 621 bacteria strains that cause pneumonia across more than 50 countries. 

This study concluded saying, ‘the continued genomic surveillance of the dynamics of the pneumococcal population with increased geographical representation in the post-vaccine period will generate further knowledge for optimizing future vaccine design.’ 

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The funding for this study was from the Bill & Melinda Gates Foundation, Wellcome Sanger Institute, and the US Centers for Disease Control.

No conflicts of interest were disclosed.