COVID-19 is primarily understood as a respiratory illness, but the virus that causes it, SARS-CoV-2, can affect numerous organ systems. The virus triggers a wide range of symptoms, meaning its presentation is not limited to fever, cough, or shortness of breath. Gastrointestinal issues are a common manifestation of the infection, and diarrhea can be the very first symptom a person experiences.
Diarrhea as an Early Indicator
Diarrhea is a recognized symptom of a COVID-19 infection, often appearing before the more commonly known respiratory issues. Approximately 10% to 20% of confirmed cases report diarrhea, establishing it as a significant presentation. The diarrhea is typically mild to moderate in severity, non-bloody, and usually consists of watery, loose stools occurring three to four times per day. Most reports indicate that COVID-related diarrhea is short-lived, typically resolving within two to six days.
As many as one in five people diagnosed with COVID-19 may present with gastrointestinal complaints as their only symptoms. Patients presenting only with digestive symptoms have also been observed to clear the virus from their bodies over a longer period compared to those with only respiratory symptoms.
The Biological Mechanism of Gut Involvement
The reason SARS-CoV-2 targets the digestive system lies in the presence of the Angiotensin-converting enzyme 2 (ACE2) receptor. This enzyme acts as the main entry point the virus uses to infect human cells. While ACE2 is present in the lungs, it is also highly concentrated on the surface of enterocytes lining the small intestine.
The virus binds to these receptors, allowing it to directly invade and damage the digestive tract tissue. This direct infection and subsequent inflammatory response disrupt the intestinal lining, leading to malabsorption and increased fluid secretion, which causes the loose, watery stools. The binding of the virus to ACE2 also disrupts the receptor’s normal function, including regulating the transport of neutral amino acids and maintaining the balance of the gut microbiome. The presence of viral RNA has been detected in the stool samples of approximately half of COVID-19 patients, supporting direct viral replication within the gastrointestinal tract.
Other Gastrointestinal Symptoms Associated with COVID
While diarrhea is common, it is part of a broader spectrum of gastrointestinal issues linked to SARS-CoV-2 infection. Other frequently reported symptoms include nausea, vomiting, abdominal pain, and a significant loss of appetite (anorexia). Nausea and loss of appetite are often the most common non-diarrhea complaints, with appetite loss affecting up to half of confirmed cases.
Abdominal pain is also reported, thought to be caused by inflammation in the intestinal lining resulting from the viral attack. In some cases, the infection can also affect the liver, leading to an elevation in liver enzymes detected in blood tests. This indicates potential injury to the liver cells, though it may not always produce noticeable outward symptoms like pain or jaundice.
When to Seek Testing and Medical Advice
If a person experiences new-onset diarrhea, especially during periods of high community transmission, it should be considered a potential indication for a COVID-19 test. Testing is particularly important if the diarrhea is accompanied by other common symptoms, such as headache, muscle aches, fatigue, or a new loss of taste or smell. Practical advice involves monitoring symptom severity and taking steps to prevent dehydration, a significant risk with any bout of diarrhea. It is advisable to consult a healthcare provider if the diarrhea lasts for more than two days or if a person is unable to keep fluids down.
Red Flags for Immediate Medical Attention
More severe symptoms warrant immediate medical attention. These concerning signs include symptoms of severe dehydration, such as significantly reduced urine output, dry skin, or mental status changes. Medical attention should also be sought for severe, sudden abdominal pain or the presence of blood in the stool. For individuals at high risk for severe illness, contacting a healthcare provider immediately upon a positive test result is important, as they may be eligible for early antiviral treatments.