COVID-19

What Gut Bacteria Reveal About COVID-19 Severity

The evidence connecting gut bacteria to COVID-19 outcomes is substantial, built on a 2025 meta-analysis pooling results from patient groups worldwide.

COVID-19 is the illness caused by the virus SARS-CoV-2, and how severely it affects someone doesn't depend on the lungs alone.

Gut bacteria shift in a measurable, consistent way as the disease grows more severe, and that shift has now been linked to how likely someone is to survive it.

A consistent drop in diversity across patient groups worldwide

A 2025 systematic review and meta-analysis pooling data from multiple patient cohorts found a significant, consistent drop in the Shannon index, a measure of how many different bacteria species are present and how evenly balanced they are, in people with COVID-19.

Faecalibacterium prausnitzii, a bacterium that produces butyrate, a compound made by fermenting fibre that calms inflammation and supports the gut lining, was significantly depleted across studies.

Enterococcus, a genus more often linked to inflammation, was significantly increased. Gut dysbiosis was tied to a 67% higher risk of death across the pooled data.

Source: Gut Microbiome Dysbiosis in COVID-19: A Systematic Review and Meta-Analysis of Diversity Indices, Taxa Alterations, and Mortality Risk

The pattern tracks severity directly, not just infection itself

A multicentre study across six hospitals found that people with moderate or severe COVID-19 had a lower ratio of two major bacterial groups, Firmicutes and Bacteroidetes, along with more Proteobacteria and less Roseburia and Lachnospira, two butyrate-producing genera, compared with people who had mild disease.

Statistical analysis found that low gut bacterial diversity nearly tripled the odds of severe COVID-19, and raised CRP, a standard blood marker of inflammation, more than tripled it.

This means the gut signal isn't just present alongside severe disease. It's one of the stronger predictors researchers identified.

Source: Gut Microbiota Diversity and C-Reactive Protein Are Predictors of Disease Severity in COVID-19 Patients

For some, the disruption outlasts the infection itself

An estimated 10% of COVID-19 survivors go on to develop long COVID, ongoing symptoms lasting three months or more after the initial infection has cleared.

A study following people with long COVID found their gut microbiomes could be split into distinct clusters based on bacterial composition alone, and these patterns tracked with lung function measured months later.

This suggests the gut disruption seen in acute COVID-19 doesn't always resolve when the virus is gone. For some people, it appears to persist and shape recovery long afterwards.

Source: Exploring Heterogeneity of Fecal Microbiome in Long COVID Patients at 3 to 6 Months After Infection

The disruption is often made worse by unnecessary antibiotics

Confirmed bacterial coinfection has been found in fewer than 10% of hospitalised COVID-19 patients in most studies, yet a systematic review found more than a third of hospitalised patients were prescribed antibiotics, and four out of five of those prescriptions went to patients with no evidence of bacterial infection at all.

Antibiotics disrupt gut bacteria regardless of why they're prescribed, so this pattern likely added a second, avoidable layer of gut disruption on top of whatever the virus itself was doing.

This doesn't undo the direct viral link described above, but it's a reminder that some of the gut damage seen in COVID-19 patients may be compounded by treatment decisions rather than the virus alone.

Source: Overprescription of antibiotics for treating hospitalized COVID-19 patients: A systematic review & meta-analysis

What this means for you

COVID-19 needs medical assessment for anyone with breathing difficulty, chest pain, or symptoms that persist beyond a few weeks. In addition, the research above shows gut bacterial diversity drops in a consistent pattern as COVID-19 grows more severe, with that disruption linked to a higher risk of death and, for some, symptoms that outlast the infection itself. A varied, plant-rich diet supports the same gut bacteria this research ties to a calmer, more resilient response to the virus. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.