Imbalances in gut microbiome may be responsible for how ill an individual will get from COVID-19 and could be why some people suffer from “long COVID”, according to new research.
Although COVID-19 is primarily a respiratory illness, evidence from scientists in Hong Kong, presented in the new edition of Gut, suggests the gut may also have a role.
Researchers at The Chinese University of Hong Kong wanted to find out if the gut microbiome could affect the immune system response to COVID-19 infection and obtained blood and stool samples and medical records from 100 hospital in-patients with laboratory-confirmed COVID-19 between February and May 2020.
They also obtained samples from 78 people without the virus who were taking part in a microbiome study before the pandemic.
The researchers classified mild illness if there was no x-ray evidence of pneumonia; moderate if patients suffered pneumonia with fever and respiratory tract symptoms; severe if patients found it very difficult to breathe normally; and critical if they needed mechanical ventilation or experienced organ failure requiring intensive care.
For this observational study, 41 of the COVID patients provided multiple stool samples while in hospital and 27 went on to provide a number of 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 between patients with and without the virus.
They found that COVID patients had higher numbers of Ruminococcus gnavus, Ruminococcus torques and Bacteroides dorei species than those who did not have the infection.
COVID patients also had far fewer of the species that can influence immune system response, such as Bifidobacterium adolescentis, Faecalibacterium prausnitzii and Eubacterium rectale.
Lower numbers of F. prausnitzii and Bifidobacterium bifidum were particularly associated with infection severity after taking account of antibiotic use and patient age.
And the numbers of these bacteria remained low in the samples collected up to 30 days after infected patients had cleared the virus from their bodies.
Analysis of the blood samples showed that the microbial imbalance found in the COVID patients was also associated with raised levels of inflammatory cytokines and blood markers of tissue damage, such as C-reactive protein and certain enzymes, suggesting that the gut microbiome might influence the immune system response to COVID-19 infection and potentially affect disease severity and outcome.
The authors write: “In light of reports that a subset of recovered patients with COVID-19 experience persistent symptoms, such as fatigue, dyspnoea 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.”
Although it is an observational study, and as such, the authors say there is mounting evidence to show that gut microbes are linked to inflammatory diseases within and beyond the gut.
“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 conclude.
Yeoh YK, Zuo T, Chung-Yan Lui G et al. Gut microbiota composition reflects disease severity and dysfunctional immune responses in patients with COVID-19. Gut 12 January 2021; doi.org/10.1136/ gutjnl-2020-323020
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