A new study has revealed that the variety and volume of bacteria in the gut, known as the microbiome, drives the severity of Covid-19 as well as the magnitude of the immune system response to the infection.

The study, published online in the journal Gut, suggested that imbalances in the make-up of the microbiome may also be implicated in persisting inflammatory symptoms, dubbed ‘long Covid’.

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As the gut is the largest immunological organ in the body, so, even when Covid-19 is primarily a respiratory disease, the gut seems to play a significant role in deciding the severity of it.

For the study, the researchers obtained blood and stool samples and medical records from 100 hospitals of patients with laboratory-confirmed Covid-19 infection between February and May 2020. They also took samples from 78 people without Covid-19 who were taking part in a microbiome study before the pandemic.

X-ray evidence

The severity of Covid-19 was classified as mild in the absence of x-ray evidence of pneumonia; moderate if pneumonia with fever and respiratory tract symptoms were detected; severe if patients found it very difficult to breathe normally; and critical if they needed mechanical ventilation or experienced organ failure requiring intensive care.

To characterise the gut microbiome, 41 of the Covid-19 patients provided multiple stool samples while in hospital, 27 of whom provided serial stool samples up to 30 days after clearance of SARS-CoV-2.

Analysis of all 274 stool samples showed that the make-up of the gut microbiome differed significantly from patient to patient with and without Covid-19, irrespective of whether they had been treated with drugs, including antibiotics.

Blood analysis

Analysis of the blood samples showed that the microbial imbalance found in Covid-19 patients was also associated with raised levels of inflammatory cytokines.

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

The authors wrote in the study: “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 the initial onset of symptoms, we posit that the dysbiotic gut microbiome could contribute to immune-related health problems post-Covid-19.”

“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 concluded.