Lung, mouth bacteria linked to severe long Covid: Study

THEBUSINESSBYTES BUREAU

NEW DELHI, OCTOBER 12, 2026

A study involving more than 700 people who were hospitalised with COVID-19 has found distinct changes in the bacteria inhabiting the mouth and lungs of patients with severe long Covid, with these microbial differences linked to respiratory impairment, brain fog and digestive problems.

Published on Monday in the European Respiratory Journal, the study suggests that changes in the body's microbiome could offer fresh clues to understanding why some people develop persistent and debilitating symptoms following a Covid-19 infection.

The findings could also open up new avenues for research into treatments for long Covid, a condition that continues to affect millions of people worldwide, although researchers cautioned that further studies are needed to establish whether the microbial changes cause the condition or occur as a consequence of infection.

The research, led by scientists from the University of Dundee in the UK, examined 771 people who had received treatment for Covid-19 at 38 hospitals across the country between February 2020 and March 2021. It was conducted as part of PHOSP-COVID, a major UK research initiative jointly funded by the National Institute for Health and Care Research and UK Research and Innovation.

Researchers classified participants into four groups according to the severity of their symptoms five months after hospital discharge, ranging from very severe cases involving major physical, mental and cognitive impairments to mild cases characterised by relatively good recovery.

Six months after discharge, scientists collected saliva samples to examine microbes in the mouth and sputum samples to analyse those in the lungs. DNA sequencing was used to identify the microorganisms present, assess their diversity and abundance, and examine their relationship with patients' symptoms.

The analysis revealed pronounced differences in the oral and lung microbiomes of people experiencing very severe long Covid compared with those who had less severe symptoms.

Importantly, changes in the airway microbiome were associated not only with reduced lung function but also with neurocognitive difficulties, including brain fog, memory problems and impaired attention and concentration. The microbial differences were also linked to gastrointestinal symptoms such as abdominal pain, nausea, diarrhoea and loss of appetite.

Among the changes identified was an increased abundance of bacteria that produce lactic acid. These changes were also associated with signs of inflammation detected in patients' blood samples, pointing to a possible relationship between microbial imbalances and inflammatory processes in long Covid.

Lead author Dr Daniela Alferes de Lima Headley said the microbiome was a strong candidate for further investigation because it plays an important role in maintaining health throughout the body.

She noted that earlier research had identified changes in the gut microbiome among people with long Covid, but examining the lung microbiome was particularly relevant given that Covid-19 primarily affects the respiratory system.

Professor James Chalmers, Chair of Respiratory Research at the University of Dundee and the study's lead researcher, said patients with the worst symptoms five to six months after infection showed substantial changes in their oral and lung microbiomes.

He said the association between airway microbes and symptoms extending beyond the lungs suggested that the microbiome could have wider implications for health.

However, Chalmers cautioned that researchers did not yet know whether the microbial differences existed before infection, emerged after Covid-19 or would persist in subsequent years. Further research is needed to determine whether these changes improve naturally over time.

He said understanding the mechanisms underlying long Covid could help scientists develop better treatments, noting that the microbiome can potentially be modified through approaches such as antibiotics, probiotics and other interventions. Such approaches, however, would require further evaluation before their effectiveness against long Covid could be established.

Professor Raquel Duarte of the University of Porto, Portugal, who was not involved in the study, said the findings provided an important basis for further research into the most disabling forms of long Covid.

She said persistent respiratory, cognitive and other symptoms continued to affect patients' ability to work, study and manage everyday activities, placing a wider burden on families, healthcare services and society.

Duarte added that longitudinal and mechanistic studies would be necessary to establish whether the observed microbial patterns could eventually help predict, prevent or treat severe long Covid.

The PHOSP-COVID research programme continues to investigate the long-term burden of the condition, including the role of inflammation and potential treatments that could help reverse its effects.