“Long covid” is the common name for a complex of complications that persist several weeks after infection with SARS-CoV-2. Scientists from Hong Kong decided to investigate whether its presence may be determined by the composition of the bacterial microflora in the intestines.
The composition of the intestinal microbiome may be associated with the risk of long-term symptoms persistence after contracting COVID-19, reports the scientific journal “Gut”.
The syndrome, popularly known as the “long covid”, is characterized by complications and / or symptoms that persist weeks after infection with the SARS-CoV-2 coronavirus. It is relatively common, with three out of four people reporting at least one symptom six months after recovering from the disease. The most common symptoms are fatigue, muscle weakness and insomnia.
Looking for a possible cause
The causes of “long covid” include an over-response of the immune system, cell damage, or the physiological consequences of a concomitant disease. However, it is still unclear how it occurs or why some people are more susceptible to “long covid”.
More and more evidence is emerging that points to the gut microbiome – that is, bacteria, fungi, and other microbes that inhabit the digestive tract. The intestine has a huge impact on immunity, and impaired immune response can affect the recovery process after infection with SARS-CoV-2 virus.
Professor Siew Ng and her team at The Chinese University of Hong Kong investigated changes in the gut microbiome of 106 patients with varying degrees of COVID-19, treated at three different hospitals from February to August 2020. The control group included 68 people who did not have any disease in the same period. Stool samples collected on admission, one month and six months later, and nine months later for 11 patients were analyzed. For the purposes of the study, “long covid” was defined as at least one symptom that persisted for four weeks after SARS-CoV-2 was eliminated from the body.
The researchers looked at respiratory, neuropsychiatric (headache, dizziness, loss of taste and smell, anxiety, poor concentration, disturbed sleep, depressed mood, poor memory, blurred vision), gastrointestinal, musculoskeletal, skin ( hair loss) and fatigue.
The average age of patients with COVID-19 infection was 48 years, slightly more than half of these people were women. 81 percent of the infection was mild to moderately severe, and 25 were treated with antibiotics.
Scientists checked for the presence of the 30 most frequently reported long-term symptoms of covid three and six months after the initial COVID-19 infection. They also used a six-minute walk test to assess aerobic capacity and endurance.
After three months, “long covid” was reported in 86 (81%) patients. Six months after the onset of the disease, 81 (76.5%) people complained of persistent symptoms. The most common symptoms were fatigue (31%), poor memory (28%), hair loss (22%), anxiety (21%), and sleep disturbances (21%).
Six months after the initial infection, no significant differences were observed between patients with “long covid” and those without it in age, gender, incidence of underlying diseases, use of antibiotics or antiviral drugs, or the course of COVID-19 infection.
What happened in the intestines
In patients with chronic covid, the number of 28 species of intestinal bacteria decreased and increased – 14. These changes were found both at admission to hospital and three and six months after discharge. Six months after discharge, patients with “long covid” had much less “friendly” F. prausnitzii and Blautia obeum and more “unfriendly” Ruminococcus gnavus and Bacteroides vulgatus than the control group.
On the other hand, the gut microbiome of people who did not develop “long covid” showed only 25 changes in bacterial species on admission to the hospital, with complete recovery after six months.
As further analyzes showed, 81 bacterial species were associated with different categories of “long covid” symptoms, with many species having more than two categories of persistent symptoms.
For example, after six months, persistent respiratory symptoms were associated with several opportunistic “bad” microbes. On the other hand, the number of species tested, the presence of which is associated with strengthening immunity, decreased drastically in people with “long covid”.
The presence of several “hostile” species of bacteria was also associated with inferior performance in the six-minute walk test among those with “long covid”.
On admission, the diversity and richness of gut bacteria in patients who subsequently developed “long covid” was significantly lower than in those who did not.
This suggests that individual gut microbial profiles may indicate increased susceptibility, the study authors said. In their view, “profiling” the microbiome can help identify those most susceptible to “covid debts”.
By its nature, an observational study cannot establish the cause of the phenomena, and was carried out on a small group of patients. However, other studies also indicated disturbances in the gut microbiome in many long-term diseases.
Overall, the altered composition of the gut microbiome is strongly associated with persistent symptoms in COVID-19 patients up to six months after SARS-CoV-2 virus clearance, the authors point out. Given the millions of people infected during the ongoing pandemic, our findings are a powerful incentive to consider modulating the microflora to facilitate rapid recovery and reduce the burden of acute COVID-19 syndrome, they add.
Main photo source: Shutterstock