Covid: Gut bacteria may influence disease severity, study suggests

A coronavirus patient's gut bacteria may influence the length and severity of their infection and their immune response to it, a new study suggests.

Researchers found that patients with Covid-19 were depleted in gut bacteria known to modify a person's immune response, and that this depletion appeared to persist 30 days after the virus had gone.

Gut bacteria — or gut microbiome — help to digest food. But research increasingly shows that gut bacteria also affect our health.

A team of researchers at The Chinese University of Hong Kong examined whether the variety and quantity of microbiome played a role in Covid-19 infections.

Researchers analysed the blood, stool and medical records of 100 Covid-19 patients. They also took samples from 78 people who did not have the disease.

The study, published in the journal Gut, found that the composition of gut microbiome had changed in Covid-19 patients, compared to those who did not have the infection.

It said that gut microbiome could be involved in the "magnitude of Covid-19 severity possibly via modulating host immune responses".

Meanwhile, analysis of blood samples showed that the gut imbalance found in the Covid-19 patients was also associated with raised blood levels of some of the molecules that mediate inflammation.

This suggests, the researchers said, that the gut microbiome might influence the immune system response to Covid-19 infection and potentially affect disease severity and outcome.

Commenting on the study, Daniel Davis, professor of immunology at the University of Manchester, said: "Our knowledge of gut microbes has exploded in recent years.

"Variations have been associated with diseases as diverse as asthma, multiple sclerosis and cancer.

"So it's perhaps not so surprising that the severity of Covid-19 also correlates with the composition of a person's microbiome.

"But the details here are important. A particularly striking finding was that distinct characteristics in a person's gut microbes persisted after clearance of the virus.

"It is possible that these changes could contribute to the symptoms of so-called long Covid.

"At the moment this idea is still speculative but it demands further investigation.

"Overall, this new research doesn't yet lead to a clear public health message in terms of treatments or therapies, but does set the scene for a hugely important realm of new science."

Professor Neil Mabbott, personal chair of immunopathology at The Roslin Institute & Royal School of Veterinary Studies at the University of Edinburgh, said: "This is an interesting study but many important questions remain.  

"Further studies are required to determine whether these changes to the gut microbiome directly affect the severity of Covid-19 in patients, or whether they are simply a consequence of the effects of the infection on the gut and the immune system.

"It is also not certain whether these differences were present in the Covid-19 patients before they succumbed to infection, and whether similar changes are observed in patients in other geographical regions."

Additional reporting by Press Association