Years after the acute crisis of Covid-19 receded from public attention, millions of people remain caught in its long shadow — unable to work, think clearly, or move through daily life without difficulty. A study of 771 hospitalized survivors, published in the European Respiratory Journal, has found that those most severely affected by long Covid carry measurably distinct bacterial communities in their mouths and lungs, with those microbial differences echoing outward into neurological and digestive symptoms as well. The research, led by scientists at the University of Dundee as part of the UK'
Severe long Covid linked to distinct oral and lung microbiome changes
Millions of people worldwide remain disabled by long Covid, affecting their ability to work, study, and manage daily activities.
The microbiome could have effects on health far more broadly
Mark
So they found that people with severe long Covid have different bacteria in their mouths and lungs. Does that mean the bacteria is causing the long Covid, or is it just a marker of it?
Mimi
That's the crucial question they can't answer yet. They found the association—the correlation is clear—but they don't know the direction of causation. Did the infection change the microbiome, or was there something about a person's microbiome that made them vulnerable to long Covid in the first place?
Luke
Right. And they only sampled people six months after discharge. They don't have baseline data from before infection, so they can't actually tell us whether these bacterial changes happened because of Covid or were already there.
Mimi
Exactly. That's why Chalmers said they need longitudinal studies—following people over years to see if the microbiome changes persist, improve, or get worse.
Mark
But if they can confirm the connection, you could theoretically treat it with probiotics or antibiotics?
Mimi
In theory, yes. That's what makes this potentially important. The microbiome is one of the few things about our biology we can actually modify with existing tools.
Luke
Though we should note—they found an association with lactic acid-producing bacteria and inflammation markers. That's interesting, but it's still one study of 771 people. We don't know if this holds up in other populations, or if treating those bacteria would actually help patients feel better.
Mark
How many people are we talking about when they say "millions affected"?
Mimi
That's global. Long Covid affects a huge number of people worldwide, though exact numbers vary depending on how you define it. The point is it's a major public health problem that's still not well understood.
Luke
And that's important context—this study is one piece of a much larger puzzle. They're looking at the microbiome, but other researchers are studying inflammation, blood clots, viral persistence. We don't yet know which of these factors, or what combination, actually drives long Covid.
Mark
So this is promising but preliminary?
Mimi
Yes. It's solid work—large sample size, published in a respected journal—but it's the beginning of understanding, not the end.
O Pulso
- Millions of people worldwide remain disabled by long Covid, yet medicine has struggled to explain why some bodies recover fully while others do not — a gap this research begins to address.
- The study found that severely affected patients carry strikingly different bacterial populations in their airways, including an overabundance of lactic acid-producing bacteria linked to inflammatory markers in the blood.
- Most unsettling is the reach of these microbial changes: lung microbiome disruptions correlate not only with breathing difficulties but also with brain fog, memory problems, nausea, and gut pain — suggesting a systemic cascade far beyond the respiratory tract.
- Researchers cannot yet say whether these bacterial shifts preceded infection, emerged because of it, or whether they persist, improve, or deepen over time — leaving the question of causation unresolved.
- Because the microbiome can be altered through antibiotics, probiotics, and other interventions, confirmed causation could open genuinely new treatment pathways for a condition that has so far resisted clear therapeutic answers.
Years after the acute crisis of Covid-19 receded from public attention, millions of people remain caught in its long shadow — unable to work, think clearly, or move through daily life without difficulty. A study of 771 hospitalized survivors, published in the European Respiratory Journal, has found that those most severely affected by long Covid carry measurably distinct bacterial communities in their mouths and lungs, with those microbial differences echoing outward into neurological and digestive symptoms as well. The research, led by scientists at the University of Dundee as part of the UK's PHOSP-COVID initiative, does not yet establish cause, but it opens a door that medicine has rarely had reason to look through before — the possibility that the invisible ecosystems living within us may help determine who recovers and who does not.
A study of more than 700 people hospitalized for Covid-19 across 38 UK hospitals has found that those living with the most severe long Covid symptoms carry distinctly different bacterial communities in their mouths and lungs — a discovery that may help explain why some people never fully recover from infection.
Led by Dr. Daniela Alferes de Lima Headley at the University of Dundee, the research enrolled 771 survivors and collected saliva and sputum samples six months after hospital discharge. Using DNA sequencing, the team catalogued the bacterial populations present and sorted participants into four groups by symptom severity — from very severe physical, mental, and cognitive impairment down to mild symptoms and good recovery.
The pattern that emerged was striking. Those with the most serious long Covid showed pronounced microbiome differences not only in their lungs, where reduced function and breathing difficulties were expected, but also in connection with brain fog, memory problems, and gastrointestinal symptoms including pain and nausea. An overabundance of lactic acid-producing bacteria in severely affected patients was also linked to inflammatory markers in their blood — suggesting the disruption extends well beyond the airways.
Professor James Chalmers, who led the research team, noted that the microbial changes appeared to influence health far beyond the lungs alone. Yet the study leaves critical questions open: researchers do not yet know whether these bacterial shifts existed before infection, arose because of it, or how they change over time.
The findings carry real therapeutic promise. Unlike genetic factors, the microbiome can be modified — through antibiotics, probiotics, or other targeted measures. If future research confirms that these bacterial changes directly contribute to long Covid symptoms, new treatment approaches could offer relief to the millions of people worldwide who remain unable to work or manage daily life. For now, the study, conducted as part of the UK's PHOSP-COVID initiative, establishes a foundation for that next, harder question: not just what is different, but why — and what can be done about it.
Researchers studying over 700 people who recovered from Covid-19 have found that those with severe long Covid carry distinctly different bacterial populations in their mouths and lungs compared to those who recovered well. The discovery, published in the European Respiratory Journal, suggests the microbiome—the community of microorganisms living in our bodies—may play a role in why some people develop debilitating long-term symptoms while others do not.
The study, led by Dr. Daniela Alferes de Lima Headley at the University of Dundee, enrolled 771 people who had been hospitalized for Covid-19 between February 2020 and March 2021 across 38 UK hospitals. Six months after discharge, researchers collected saliva samples from participants' mouths and sputum samples from their lungs, then used DNA sequencing to catalog which bacteria were present and in what quantities. They sorted participants into four groups based on symptom severity five months post-discharge: very severe (serious physical, mental, and cognitive impairment), severe (serious mental and physical problems but not cognitive), moderate (primarily cognitive difficulties), and mild (few symptoms, good recovery).
The results showed a clear pattern. People with very severe long Covid had pronounced differences in their oral and lung microbiomes compared to those with milder outcomes. More striking still, the bacterial changes correlated not only with respiratory problems—reduced lung function, difficulty breathing—but also with neurological symptoms like brain fog and memory problems, as well as gastrointestinal issues including pain, nausea, and diarrhea. Among the notable findings was an overabundance of lactic acid-producing bacteria in severely affected patients, a change that also appeared linked to inflammatory markers detected in their blood.
Professor James Chalmers, who led the research team, emphasized the breadth of the connection. The microbiome changes in the airways seemed to influence health far beyond the lungs alone, he noted. Yet critical questions remain unanswered. Researchers do not yet know whether these bacterial shifts preceded Covid infection or developed as a result of it. They also cannot say whether the microbiome changes persist, improve, or worsen over time in affected patients—a gap that future studies will need to address.
The implications for treatment are potentially significant. Unlike genetic factors, which cannot be easily altered, the microbiome can be modified through antibiotics, probiotics, or other interventions. If researchers can confirm that microbiome changes directly cause or substantially contribute to long Covid symptoms, targeted treatments targeting the bacterial composition could offer relief to millions of people worldwide who remain unable to work, study, or manage daily activities due to the condition. For now, the study provides what researchers describe as a foundation for further investigation into both the mechanisms underlying long Covid and potential therapeutic approaches. The work is part of PHOSP-COVID, the UK's flagship long Covid research initiative, which continues examining inflammation and other factors that might explain why some people never fully recover from Covid-19 infection.
Citações Notáveis
People who had the worst symptoms five to six months after Covid infection had big changes in the microbiome in their mouth and lungs, and these changes were linked not just to lung problems, but also to symptoms like brain fog and gut symptoms.— Professor James Chalmers, University of Dundee
Understanding what causes long Covid could lead to better treatments; the microbiome can be changed using antibiotics, probiotics or other measures.— Professor James Chalmers, University of Dundee
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