The bacteria in your gut may play a role in the severity of COVID-19 infection and the strength of your immune system response, a new study suggests.
Not only that, imbalances in the microbiome may cause continued inflammatory symptoms, often called "long-haul" COVID, the researchers added.
"Imbalance in the microbiome contributes to the severity of COVID-19, and if it persists after viral clearance, could contribute to persistent symptoms and multi-system inflammation syndromes like long COVID syndrome," said lead researcher Dr. Siew Ng, a professor from the Institute of Digestive Disease at the Chinese University of Hong Kong.
"Restoration of the missing beneficial bacteria might boost our immunity against SARS-CoV2 virus and hasten recovery from the disease," she said. "Managing COVID-19 should not only aim at clearing the virus, but also restoring the gut microbiota."
The study, however, can't prove that imbalances in the microbiome cause COVID-19 to be more severe, only that there appears to be an association between the virus and bacteria in the gut, Ng said.
But evidence is growing that gut bacteria are linked to inflammatory diseases, she noted.
For the study, the researchers studied blood and stool samples from 100 patients with COVID-19 and from 78 people without the infection who were part of a microbiome study before the pandemic began.
They found that in 274 stool samples the gut microbiome differed significantly between patients with and without COVID-19, regardless if they had been given drugs, including antibiotics.
For example, those with COVID-19 had fewer types of bacteria that can affect the immune system response than those without the infection. The reduced number of these bacteria was linked to the severity of the infection.
Moreover, the number of these bacteria remained low up to 30 days after infected patients had cleared the virus, the researchers found.
COVID-19 triggers the immune system to make inflammatory cytokines, and in some cases, this response can be excessive, causing widespread tissue damage, septic shock and organ failure.
Analysis of the blood samples found that the microbial imbalance in the COVID-19 patients was linked with high levels of inflammatory cytokines and blood markers of tissue damage, such as C-reactive protein.
One U.S. expert not part of the study pointed out that one's microbiome reacts to all kinds of conditions that may or may not be related to COVID-19.
"It's pretty clear that stool biodiversity does change in response to many things, including age, diet, underlying autoimmune disease and antibiotic exposures," said Dr. Arun Swaminath, chief of the division of gastroenterology at Lenox Hill Hospital in New York City.
The critical question is whether these changes are unique to COVID-19 or are commonly seen in sick patients who may have been hospitalized for non-COVID related illnesses, he said.
"Some of the early published data among populations with altered gut microbiomes, such as patients with inflammatory bowel disease who are infected with COVID-19, do not experience worse outcomes compared to the general population, so the idea of having altered gut microbiome at baseline doesn't seem to imply worse inflammation from COVID-19," Swaminath said.
"However, Ng's work may help us identify those who haven't recovered from COVID-19 infection using stool biodiversity testing," he added.
The report was published online Jan. 11 in the journal Gut.