COVID-19: Gut bacteria may influence severity

• A recent study investigated links between the gut microbiome and COVID-19.
• The authors conclude that an individual’s gut microbiome may affect how the body responds to a SARS-CoV-2 infection.
• Gut bacteria might influence both the short- and long-term effects of infection.

More than 92 million people worldwide have tested positive for SARS-CoV-2, the virus that causes COVID-19, and a little more than half of these people have recovered so far.

However, recovering from COVID-19 does not mean that a person’s experience with the virus is over. Research indicates that around 32% of people experience long-term health effects from COVID-19, which scientists have dubbed “long COVID.”

A new paper that appears in the journal Gut suggests that the composition of the gut microbiome at the time of infection may impact whether someone experiences long COVID.

The paper also concludes that gut bacteria may affect the severity of the symptoms during the infection.

Function of the gut microbiome

The gut microbiome plays a significant role in health. The gut is home to trillions of microorganisms, including more than 1,000 species of bacteria.

Some bacteria in the gut help digest food and may also reduce the risk of developing certain diseases.

On the other hand, some bacteria may contribute to the development of certain types of cancer, play a role in obesity, and even impact mental health.

Sometimes, the bacteria in the gut can become unbalanced, which scientists refer to as dysbiosis. This can occur as a result of taking antibiotics or eating a diet of highly processed food. Dysbiosis can contribute to the development of health issues.

The study

No two people have the same gut microbiome, but there are certain types of bacteria that everyone might expect to have. This was the basis for the study, which was co-led by Yun Kit Yeoh. Yeoh works for the Department of Microbiology at The Chinese University of Hong Kong.

The researchers collected blood and stool samples from 100 patients who tested positive for SARS-CoV-2 between February and May 2020 from two hospitals in Hong Kong. They compared the data collected from these individuals to samples obtained from 78 participants before the pandemic started.

The study showed that patients with COVID-19 had higher numbers of certain bacteria, including Ruminococcus gnavus, Ruminococcus torques, and Bacteroides dorei. R. gnavus, for example, is a bacterium associated with inflammatory bowel disease.

The samples from those with COVID-19 also had reduced numbers of other bacteria species than those without the virus. They had lower counts of Bifidobacterium adolescentis, Faecalibacterium prausnitzii, and Eubacterium rectale. These species, as the authors explain, have “immunomodulatory potential.”

Additionally, the researchers found raised cytokine levels in people who had the virus. Cytokines are important for cellular communication; the immune system produces inflammatory cytokines in response to viral infections.

The authors explain that during COVID-19, the body’s inflammatory response can be “overaggressive” and cause a cytokine storm. This can cause “widespread tissue damage, septic shock, and multi-organ failure.”

Overall, the authors conclude: “Associations between gut microbiota composition, levels of cytokines, and inflammatory markers in patients with COVID-19 suggest that the gut microbiome is involved in the magnitude of COVID-19 severity possibly via modulating host immune responses.”

Antibiotics

The researchers mention that doctors should exercise caution if they decide to use antibiotics to treat someone with COVID-19.

“It is still possible that a higher prevalence of antibiotic administration in severe and critical patients could worsen inflammation,” the authors write.

They also conclude that “antibiotics are unlikely to be associated with improved patient outcomes assuming no bacterial coinfections but, in contrast, could exacerbate and prolong gut microbiota dysbiosis in patients with COVID-19.”

In addition to the gut microbiome contributing to worse COVID-19 symptoms, the researchers believe that gut bacteria might play a role in the development of long COVID.

The authors write that “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.”

Study implications

Knowing that gut health may affect how someone experiences COVID-19, this study may help shape what recommendations medical professionals make in terms of precautions to take. The authors write:

“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.”

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