Gut bacteria may influence severity of COVID complications, study suggests

Close-up portrait of an african businesswoman with face mask after returning back to work at office. Woman with protective face mask standing in office and staring at camera.
A new study has linked coronavirus complications to varying gut bacteria levels in hospitalised patients. (Posed by a model, Getty Images)

A coronavirus patient’s gut bacteria may play a role in the severity of their symptoms, research suggests.

The micro-organisms in our gastrointestinal tract do far more than just digest food, with studies suggesting they help control a person’s weight, regulate mood and even communicate with the immune system.

To better understand the role of gut bacteria amid the pandemic, scientists from The Chinese University of Hong Kong analysed the stool samples and medical records of 100 patients hospitalised with the coronavirus-related disease COVID-19, as well as 78 people without the infection.

Results revealed the hospitalised patients had varying numbers of specific gut bacterial species, some of which were particularly associated with disease severity.

Read more: Pfizer vaccine shows efficacy signs against new coronavirus variants

The microbial imbalance was also linked to raised markers of inflammation and tissue damage.

In severe cases, the immune system can over-react to the coronavirus, triggering widespread inflammation that leads to septic shock and even multi-organ failure.

Experts have generally welcomed the study as early-stage research, however, some stressed the results are “speculative” and “far-reaching”.

Faecalibacterium prausnitzii bacteria, illustration. This is one of the most abundant bacterial species found in the human gut. Its presence is thought to give protection against a number of gut disorders including inflammatory bowel disease, Crohn's disease and colon cancer.
Gut bacteria have long been linked to immune system health. (Stock, Getty Images)

The coronavirus was initially considered a respiratory infection, however, reports of brain fog, diarrhoea and skin rashes demonstrate almost any part of the body can be affected.

Given the role gut bacteria play in a person’s immune response, the scientists set out to uncover how the microbiome – defined as the body’s micro-organism community – may influence coronavirus outcomes.

They therefore analysed the stool samples and medical records of people with a confirmed coronavirus infection between February and May.

These were compared against 78 people who did not have the coronavirus, but provided stool samples as part of a microbiome study pre-pandemic.

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Although all the coronavirus-positive participants were hospitalised, relatively mild cases were defined as having no evidence of pneumonia on an X-ray.

Moderate incidents had pneumonia with a fever, as well as “respiratory tract symptoms”.

Critical patients required ventilation or were experiencing organ failure that needed intensive care.

Of the 100 patients, 41 provided multiple stool samples in hospital, while 27 gave samples up to 30 days after supposedly clearing the coronavirus.

Watch: Can you catch coronavirus twice?

The results, published in The BMJ journal Gut, revealed gut bacteria make-up differed significantly between the participants with and without the coronavirus.

This is regardless of whether the individuals had taken antibiotics, which can change a person’s gut bacteria.

Overall, the coronavirus patients had higher numbers of the species Ruminococcus gnavus, Ruminococcus torques and Bacteroides dorei.

They also had a far lower number of species that can influence the immune response, like Bifidobacterium adolescentis, Faecalibacterium prausnitzii and Eubacterium rectale.

Lower numbers of Faecalibacterium prausnitzii and the species Bifidobacterium bifidum were particularly associated with infection severity.

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The results also revealed these numbers remained low up to 30 days after the infected patients went on to test negative.

The scientists wondered whether an imbalance to a person’s gut bacteria may be involved in so-called “long COVID”, when a former patient continues to endure complications despite testing negative for the infection.

“In light of reports that a subset of recovered patients with COVID-19 experience persistent symptoms, such as fatigue, dyspnoea [breathlessness] and joint pains, some over 80 days after initial onset of symptoms, we posit that the dysbiotic gut microbiome could contribute to immune-related health problems post-COVID-19,” they wrote.

Speaking of this finding, Dr Daniel Davis from the University of Manchester added: “At the moment this idea is still speculative but it demands further investigation, especially given the huge importance of understanding long COVID.”

The scientists stressed their study was observational. It is therefore unclear whether variation to gut bacteria triggers coronavirus complications, or vice versa.

“Antibiotic therapy, hospital admission and infections will change the microbiome,” said Dr Willem van Schaik, from the University of Birmingham.

“It is entirely inappropriate to suggest the microbiome composition determines COVID-19 severity or the risk of long COVID.

“This study does not provide data to support that far-reaching claim.”

Nevertheless, the scientists hope their results could help medics better treat coronavirus patients.

“Bolstering of beneficial gut species depleted in COVID-19 could serve as a novel avenue to mitigate severe disease, underscoring the importance of managing patients’ gut microbiota during and after COVID-19,” they wrote.

Professor Angus Dalgleish from the University of London agreed, adding: “This is a good study and the results make sense to further optimise diet and reduce inflammation in those with and at risk of COVID.”

Many experts stressed, however, much more research is required.

“Until it can be clearly evidenced that changing the gut microbiome alters COVID-19 risk, it would not be appropriate to suggest measures to improve gut health would increase resilience to COVID-19,” said Dr Kaitlin Wade, from the University of Bristol.

Watch: What is long COVID?