Bacterial Strain, Not Just Pollution Levels, Shapes Disease Risk in South Africa, Study Finds

JOHANNESBURG – Air pollution may increase the risk of deadly bacterial infections, but new research suggests that the strain of bacteria a person carries can determine how quickly and severely that risk emerges.

The finding comes from a study published on Monday in Nature Microbiology, based on nearly two decades of South African health surveillance data and about 59,000 cases of invasive pneumococcal disease (IPD).

Researchers from the Wellcome Sanger Institute, South Africa’s National Institute for Communicable Diseases (NICD), the Barcelona Supercomputing Centre and collaborating institutions analysed 19 years of data collected through South Africa’s national GERMS-SA surveillance programme.

Their findings suggest that the relationship between air pollution and invasive pneumococcal disease is more complicated than simply measuring pollution levels. Different strains of Streptococcus pneumoniae appear to respond to environmental exposure differently, including in the timing of when infection develops.

Three bacterial strains stood out

Streptococcus pneumoniae commonly lives in the nose and throat without causing illness. Globally, the bacterium is estimated to be carried by almost 20% of adults, while between 40% and 60% of children in South Africa are thought to carry it at any given time.

The bacteria can become dangerous when they move beyond the upper respiratory tract and enter the lower respiratory tract or bloodstream.

This can result in invasive pneumococcal disease, including bacterial sepsis, pneumonia and meningitis.

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The study found that three pneumococcal serotypes, identified as 14, 19A and 8, were associated with the highest risk of invasive disease following exposure to air pollution.

But the researchers found another important difference: the effect of pollution was not immediate or uniform across the strains.

Some serotypes were associated with disease occurring shortly after exposure, while others showed an apparent increase in disease risk several weeks later.

That means the same level of environmental exposure may not produce the same disease pattern across different bacterial strains.

A long-standing gap in understanding

Scientists have known for years that different pneumococcal serotypes can produce different rates of infection among different populations.

What has been less clear is how environmental conditions, including air pollution, temperature and humidity, interact with those strains and how the resulting risks vary according to age.

The South African dataset provided researchers with an opportunity to examine those relationships over a long period.

Professor Anne von Gottberg, co-senior author of the study and a researcher at the NICD, said the findings add to evidence linking air quality with infectious disease.

“Invasive pneumococcal diseases are a significant public health issue in South Africa and globally,” von Gottberg said.

“This research adds to the ongoing evidence that air quality greatly impacts our health and shows that it has different effects depending on the strain of bacteria that is found in an area. We need to focus on monitoring and improving air quality in areas with high disease risk to prevent or reduce some of these infections.”

Professor Rachel Lowe, co-senior author based at the Barcelona Supercomputing Centre and the Catalan Institution for Research and Advanced Studies, said the findings should also be viewed against wider environmental changes.

“Climate change and rapid urbanisation are fundamentally altering the environmental conditions that influence the risk of infectious disease,” Lowe said.

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She said linking long-term climate and air-quality monitoring with health outcomes could help researchers understand how changing environmental conditions affect public health.

Protecting vulnerable communities, she added, would require cooperation between different sectors and health strategies capable of responding to changing environmental conditions.

Risk may vary from one person to another

Dr Sophie Belman, the study’s first author, researched while at the Wellcome Sanger Institute and the Barcelona Supercomputing Center and is now based at Yale School of Public Health.

She said the research points towards a more detailed understanding of how environmental exposure translates into disease.

“While we found that temperature and air pollution generally increase the risk of invasive pneumococcal diseases, such as bacterial meningitis, our research also suggests that it is the bacterial subtypes a person is carrying that modulate infection rates,” Belman said.

“The strain of bacteria impacts the timing of disease and who might be more at risk depending on their respiratory microbiome, meaning that the risk is not the same in every situation or for every person.”

Belman said the researchers hope to test whether the patterns identified in South Africa are also present elsewhere.

“By extending our findings to other parts of the globe, we will better understand who has the highest health risk from environmental exposures, and what factors need to be addressed in different regions, such as improving air quality in cities,” she said.

Why the findings matter in South Africa

The research has particular relevance for South Africa, where exposure to air pollution varies significantly between communities.

Industrial areas such as the Vaal Triangle and Mpumalanga’s Highveld have experienced significant air-pollution pressures, while some households in informal settlements rely on coal and wood for heating and cooking.

The study suggests that understanding disease risk may require more than monitoring pollution levels alone.

Tracking which pneumococcal serotypes are circulating in particular communities could potentially help researchers and health authorities better understand when increases in invasive disease are likely to occur and which groups may be most affected.

That could have implications for disease surveillance and health-system planning, particularly during periods when respiratory infections typically increase.

South Africa’s existing GERMS-SA surveillance system provides a foundation for this kind of analysis because it combines information on invasive bacterial disease across the country over extended periods.

The researchers now want to determine whether the strain-specific patterns identified in South Africa can be replicated in other parts of the world.

Different countries have different pollution profiles, healthcare systems, environmental conditions and circulating pneumococcal serotypes. Those differences will be important in determining whether the findings apply beyond the South African population.

The broader objective is to understand not only whether environmental exposures increase the risk of invasive bacterial disease, but also which bacterial strains, people and time periods are associated with the greatest risk.

For public health authorities, that could eventually provide a more precise way of anticipating disease patterns as air quality and environmental conditions change.