Long Covid severity linked to changes in mouth and lung bacteria, study finds

• A UK study found differences in mouth and airway bacteria among people with more severe long Covid symptoms

• The microbial changes were associated with breathing difficulties, brain fog and digestive problems

• The findings could guide further research, but do not establish that the bacterial changes cause long Covid

People with severe long Covid have distinct differences in the bacteria found in their mouths and airways, according to research that could help explain why symptoms persist after the initial infection.

The study, published in the European Respiratory Journal, found that these microbial differences were associated with breathing problems as well as cognitive and digestive symptoms. Researchers said the findings could support further investigation into the condition and potential treatments.

Led by researchers at the University of Dundee in the UK, the study examined 771 people treated for Covid-19 at 38 British hospitals between February 2020 and March 2021.

Participants were placed into four groups according to their symptoms five months after leaving hospital. These ranged from mild symptoms and good recovery to very severe illness involving substantial physical, mental and cognitive difficulties.

At six months after discharge, researchers collected saliva and sputum samples to examine microbes in the mouth and airways. They used DNA sequencing to identify the organisms present, then compared their diversity and abundance with participants’ symptoms.

People in the most severely affected group showed marked microbial differences compared with those whose long Covid was less severe.

The researchers also identified differences associated with reduced lung function, including limitations in how much air the lungs could hold or how easily air moved in and out.

Other changes were linked to neurocognitive difficulties, such as brain fog and problems with memory, attention and concentration. Associations were also found with digestive symptoms, including abdominal pain, nausea, diarrhoea and loss of appetite.

One finding was an increased abundance of bacteria that produce lactic acid. This was associated with long Covid symptoms and signs of inflammation detected in blood samples.

Lead author Daniela Alferes de Lima Headley said previous research had identified changes in gut bacteria among people with long Covid. Examining the lung microbiome was therefore an important next step, given Covid-19’s effects on the respiratory system.

She said the microbiome helps maintain health throughout the body, making it a possible contributor to a condition that affects multiple organs.

James Chalmers, chair of respiratory research at Dundee, said the largest changes in mouth and lung bacteria occurred among those with the worst symptoms five to six months after infection.

The associations with brain fog and digestive problems suggested that airway microbes might have implications beyond respiratory health, he said.

However, the findings demonstrate associations rather than a proven cause of long Covid. The study also focused on previously hospitalised patients, leaving further research needed to establish whether similar patterns occur after milder infections.

With IANS inputs