The researchers found that individuals with Long Covid have an altered bacteria composition in their mouths and lungs compared with patients with a more complete recovery after COVID-19. The observations point to the microbiome the indigenous bacteria that live in and on our bodies as a potential source of insight into why a certain group of people continue to experience respiratory, cognitive, and digestive symptoms long after initial infection.
The research was conducted as part of the UK Post-hospitalisation COVID-19 study, PHOSP-COVID, and involved 771 people who had been treated for COVID-19 at 38 hospitals in the UK. Experts analysed samples taken after six months of being discharged and analysed microbial differences against the severity and nature of ongoing symptoms.
The study had also divided subjects per severity of continuing health problems. These categories varied from relatively mild symptoms and good recovery to very severe impairment of physical health, mental health and cognitive functioning.
“In particular, we identified differences in oral and respiratory microbiologies of very severe subjects. We also found differences in bacterial compositions in the mouth of patients with decreased lung function.”
One of the study’s notable findings was that microbiome differences were not limited to respiratory symptoms. Persistent neurocognitive problems, including difficulties with concentration and memory commonly described as brain fog, were connected to distinct oral microbiome patterns.
The researchers also found that GI symptoms like digestive discomfort and appetite change were linked to sputum microbiome diversity. This finding, the authors noted, suggested that microbes from multiple organs or regions of the body could be linked by immune signalling, inflammation, and cross-talk between organ systems.
They also found that more lactic acid bacteria were found in microbial networks where health outcomes were bad. More of the lactic acid bacteria were related to higher levels of inflammatory proteins in the blood samples. This doesn’t mean that all the lactic acid bacteria are necessarily ‘bad’there are many different types that can be beneficial in other situations.
The results contribute to increasing scientific attention on the link between the microorganisms and long-term health after COVID-19. Earlier research examined the gut microbiome and saw some changes in the types and variety of bacteria and other microbes in those with lingering symptoms.
The new work expands that line of inquiry to study both the oral and lower respiratory microbiomes together. One explanation: microbial changes set off inflammation or immune responses that linger after the infection is cleared. Or perhaps residual illness, medication use, altered diet or other factors disrupt microbial communities during recovery.
The study can’t yet identify, which explanation is correct. The presence of the relationships the researchers found between microbiomes and other symptoms do not show if the microbiome causes Long Covid, is an effect of it or something else entirely. We will need to wait for further work to show us the answers.