The gut microbiome: a missing link in understanding the gastrointestinal manifestations of COVID-19?

Coronavirus disease 2019 (COVID-19), which is caused by infection with SARS-CoV-2, presents with a broad constellation of both respiratory and nonrespiratory symptoms, although it is primarily considered a respiratory disease. Gastrointestinal symptoms-including nausea, abdominal pain, vomiting, and diarrhea-rank chief among these. When coupled with the presence of viral RNA in fecal samples, the presence of gastrointestinal symptoms raises relevant questions regarding whether SARS-CoV-2 can productively infect the upper or lower gastrointestinal tract. Despite the well-documented prevalence of gastrointestinal symptoms and the high rate of SARS-CoV-2 fecal RNA shedding, the biological, clinical, and epidemiological relevance of these findings is unclear. Furthermore, the isolation of replication-competent virus from fecal samples has not been reproducibly and rigorously demonstrated. Although SARS-CoV-2 shedding likely occurs in a high proportion of patients, gastrointestinal symptoms affect only a subset of individuals. Herein, we summarize what is known about gastrointestinal symptoms and fecal viral shedding in COVID-19, explore the role of the gut microbiome in other respiratory diseases, speculate on the role of the gut microbiota in COVID-19, and discuss potential future directions. Taking these concepts together, we propose that studying gut microbiota perturbations in COVID-19 will enhance our understanding of the symptomology and pathophysiology of this novel devastating disease.