A large registry study of 771 adults who were hospitalized with COVID-19 found that those with long COVID had substantially different bacterial communities in their mouths and sputum compared with people who had milder persistent symptoms. The greatest losses in bacterial diversity were seen in patients with the most severe impairment around six months after the acute infection. The findings were published in the European Respiratory Journal.
Specific symptom patterns appeared to track with different microbial profiles. Reduced lung function was linked to a distinct oral microbiota, while persistent neurocognitive symptoms also showed a unique oral signature. Gastrointestinal symptoms, by contrast, correlated with a distinct sputum microbiota. The researchers also observed a shift toward lactic acid bacteria that was associated with elevated inflammatory proteins in the blood, suggesting a possible link between airway bacteria and chronic inflammation.
The study's authors caution that they cannot determine whether the microbiome changes came before the infection, resulted from it, or were influenced by hospitalization and general respiratory illness. There were no pre-COVID samples and no non-COVID control group. Still, they note that both microbiota differences and chronic inflammation appear to be key features of ongoing COVID-19, and they call for mechanistic studies and eventual treatment trials that might test antibiotics, probiotics, or other ways of modifying the microbiome.