Study Finds Distinct Microbiomes in People With Severe Long COVID

A study published in the European Respiratory Journal reports distinct bacterial differences in people with long COVID. More than 700 participants showed clear variations in the mix of bacteria living in their mouths and lungs. These findings suggest a link between the microbiome and the condition affecting millions globally.

The research involved 771 people who received treatment for COVID-19 at 38 hospitals across the United Kingdom. Participants were tracked as part of the PHOSP-COVID project between February 2020 and March 2021. Researchers compared symptom severity five months after hospital discharge to categorize recovery levels.

Scientists collected saliva samples from mouths and sputum from lungs six months after patients left the hospital. DNA sequencing identified which microbes were present in these samples from every group. The team analyzed the variety and quantities of bacteria to compare against reported symptoms.

People with very severe long COVID displayed distinct microbiome patterns compared to those without severe symptoms. These differences correlated with respiratory issues, cognitive difficulties like brain fog, and digestive problems. Specific findings included reduced lung function alongside pain and nausea in the gut.

The study identified an overabundance of bacteria that produce lactic acid among those with symptoms. This bacterial change was linked to signs of inflammation found in patient blood samples. Such markers suggest a biological pathway connecting microbes to systemic health effects.

Dr. Daniela Alferes de Lima Headley from the University of Dundee led the study. She noted that while the cause of long COVID is unknown, the microbiome plays a key role in maintaining body health. Prior studies have shown gut changes, but researchers reasoned looking at the lungs made sense for a respiratory disease.

James Chalmers, chair of respiratory research at the University of Dundee, highlighted that uncertainty remains about timing. It is unclear whether these microbiome changes happened before or after the infection occurred. Researchers also do not yet know if these changes improve in subsequent years.

The findings could point to new treatments using antibiotics or probiotics to change the microbiome. However, independent experts say further research is needed before clinical use becomes possible. Raquel Duarte of the European Respiratory Society emphasized that millions still face disabling consequences.