One of the many issues that have flummoxed scientists researching COVID-19 is the nose-to-toes diversity of its symptoms, which extend well beyond the usual range of respiratory infections: from loss of smell to blood clots and stroke to limb pain and discolored COVID toes. One of the most common nonrespiratory manifestations is gastrointestinal trouble. As many as 50 percent of COVID patients have nausea, diarrhea and/or abdominal pain. And according to a Canadian review paper, for 16 percent in one large study, those were the only symptoms.
Research indicates that SARS-CoV-2—the virus that causes COVID—can directly attack the epithelial cells that line the GI tract, entering via the molecular doorway of angiotensin‐converting enzyme 2 (ACE2). These cells express high levels of ACE2, as do the cells lining the lungs, the primary site of infection.link