Gut Bacteria May Impact Severity Of COVID-19 Infections

People who become severely ill and hospitalized with COVID-19 have a different make-up of bacteria in their guts compared to healthy people. Alpha Tauri 3D Graphics/Shutterstock.com

The trillions of microorganisms that live in your gut might play a role in how well you cope with COVID-19, as per a new study. Equally, gut bacteria might also help to explain the lingering symptoms of the coronavirus infection known as “long COVID.”

It’s becoming increasingly well-understood that the gut microbiome – the army of bacteria, archaea, and fungi that live in the digestive tract – plays a key role in the body’s immune system. In a new study, researchers from the Chinese University of Hong Kong have found that people who become severely ill and hospitalized with COVID-19 have a different make-up of bacteria in their guts compared to healthy people, suggesting a person’s gut microbiome may affect the immune system response to COVID-19 infection.

Researchers collected 100 poop samples from hospital patients with COVID-19, and compared them to samples taken from 78 people before the COVID-19 pandemic. The team found that their microbiome differed hugely. Perhaps most significantly, people hospitalized with COVID-19 had far fewer of the species of bacteria that are known to influence immune system response, such as Bifidobacterium adolescentis, Faecalibacterium prausnitzii, and Eubacterium rectale. In fact, levels of these bacteria were linked with how severe the patients' illness was. COVID-19 patients also had notably higher numbers of Ruminococcus gnavus, Ruminococcus torques, and Bacteroides dorei. 

Low levels of the bacteria linked to the immune system were also found in the COVID-19 patients up to 30 days after they had cleared the virus from their bodies. The researchers argue this microbial imbalance could help to answer why so many people who are sick with COVID-19 appear to suffer from “long COVID,” namely fatigue, joint pains, and other lurking symptoms long after their recovery. 

This study was only an observational study and, although it found a compelling link, it can't firmly establish a cause. It’s impossible to definitely say, for example, whether people who were hospitalized with COVID-19 had a less diverse microbiome due to other factors, such as whether they smoke.

Nevertheless, another study released this week has also weighed in on the wider question of how gut microbes are linked to illness. As part of the largest in-depth nutritional study in the world, scientists from King's College London identified a number of “good” bacteria species that are linked to a lower risk of certain diseases, and “bad” species linked to a heightened risk of illnesses. As reported in the journal Nature Medicine, the findings even suggest the microbiome has a greater association with disease biomarkers than other factors, such as genetics.

"We were surprised to see such large, clear groups of what we informally call 'good' and 'bad' microbes emerging from our analysis. It is also exciting to see that microbiologists know so little about many of these microbes that they are not even named yet," Dr Nicola Segata, study author, professor, and principal investigator of the Computational Metagenomics Lab at the University of Trento in Italy, said in a statement.

Scientists are only just starting to get to grips with how bacteria in our guts may help and hinder our immune systems, but it's becoming increasingly clear that human health is intrinsically linked to these microorganisms, not least when it comes to COVID-19.

For more information about COVID-19, check out the IFLScience COVID-19 hub where you can follow the current state of the pandemic, the progress of vaccine development, and further insights into the disease.

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