Involvement of digestive system in COVID-19: manifestations, pathology, management and challenges

The pandemic of novel coronavirus disease (COVID-19) has developed as a tremendous threat to global health. Although most COVID-19 patients present with respiratory symptoms, some present with gastrointestinal (GI) symptoms like diarrhoea, loss of appetite, nausea/vomiting and abdominal pain as the major complaints. These features may be attributable to the following facts: (a) COVID-19 is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and its receptor angiotensin converting enzyme 2 (ACE2) was found to be highly expressed in GI epithelial cells, providing a prerequisite for SARS-CoV-2 infection; (b) SARS-CoV-2 viral RNA has been found in stool specimens of infected patients, and 20% of patients showed prolonged presence of SARS-CoV-2 RNA in faecal samples after the virus converting to negative in the respiratory system. These findings suggest that SARS-CoV-2 may be able to actively infect and replicate in the GI tract. Moreover, GI infection could be the first manifestation antedating respiratory symptoms; patients suffering only digestive symptoms but no respiratory symptoms as clinical manifestation have also been reported. Thus, the implications of digestive symptoms in patients with COVID-19 is of great importance. In this review, we summarise recent findings on the epidemiology of GI tract involvement, potential mechanisms of faecal-oral transmission, GI and liver manifestation, pathological/histological features in patients with COVID-19 and the diagnosis, management of patients with pre-existing GI and liver diseases as well as precautions for preventing SARS-CoV-2 infection during GI endoscopy procedures.