The significance of the gut microbiome in post-COVID-19 gastrointestinal symptoms

Editor – I read with interest the article by Cooney and colleagues in which 43.8% of the patients studied reported new-onset gastrointestinal (GI) symptoms in the 6 months after their acute COVID-19 illness and the authors suggest the possible existence of a post-COVID-19 irritable bowel syndrome (IBS).¹ The authors discuss the presence of the angiotensin converting enzyme 2 (ACE-2) receptor throughout the GI tract, which serves as the SARS-CoV-2 receptor, as an important potential factor. However, the potential relevance of gut microbiome disturbance in patients with COVID-19 was not discussed.

Significant alterations in the gut microbiome have been demonstrated in patients with COVID-19 compared with non-COVID-19 controls, characterised by an abundance of opportunistic pathogens and a reduction in certain gut commensals known to have anti-inflammatory properties including Faecalibacterium prausnitzii and Bifidobacterium.² A meta-analysis also found significant reductions in both of these gut commensals in IBS patients when compared with healthy controls.² Additionally, multiple studies have reported reduced levels of F prausnitzii in the gut of patients with inflammatory bowel disease.⁴

The degree of gut dysbiosis in COVID-19 has been demonstrated to correlate with the severity of COVID-19 illness and dysbiosis has been shown to persist in a subset of patients even after clearance of SARS-CoV-2 RNA.^5,6 However, antibiotics are also likely to play a role, at least in part, supported by the fact that alterations in the gut microbiome have also been identified in patients treated for (non-COVID-19) community-acquired pneumonia.⁶ Empirical broad-spectrum antibiotic usage in patients hospitalised with COVID-19 is high (>60%), particularly in individuals with severe disease and, in the study by Cooney et al, 97% were admitted for inpatient care with 36% requiring intensive care unit care.^1,7 Broad-spectrum antibiotics have been shown to negatively impact the gut microbiota resulting in reduced microbial diversity and potentially beneficial bacteria.⁸ Furthermore, an association between the use of certain antibiotic classes (macrolides and tetracyclines) within the prior 12 months and the development of IBS has been demonstrated.⁹ Gut microbiome dysbiosis may therefore play a key role in the development of post-COVID-19 GI symptoms and this area needs further study.