COVID-19, caused by the SARS-CoV-2 virus, is widely known for its effects on the respiratory system, but the illness often involves a much broader range of symptoms. The virus can affect multiple body systems because it gains entry into human cells by binding to the Angiotensin-Converting Enzyme 2 (ACE2) receptor, which is expressed throughout the body. This mechanism explains why symptoms are highly variable and can manifest in areas beyond the lungs, including the digestive tract.
Diarrhea as an Early Indicator
Diarrhea can be the first sign of a COVID-19 infection, appearing before or alongside typical respiratory complaints like cough or fever. While respiratory symptoms remain the most common initial presentation, gastrointestinal (GI) symptoms were reported as the first sign of COVID-19 in approximately 14% to 22% of infected individuals.
For those who experience it, COVID-related diarrhea is usually mild and lasts for an average of two to six days. It is often described as watery and may occur three to four times daily. Although diarrhea can precede other symptoms, patients typically develop fever or respiratory issues within a few days. A notable subgroup of patients may experience digestive issues as their only symptom.
Prevalence and Scope of Digestive Issues
Digestive symptoms are a frequent occurrence at some point during the infection, with some studies reporting that over 60% of hospitalized patients experienced at least one gastrointestinal complaint. While diarrhea is a recognized manifestation, its overall prevalence varies widely, ranging from about 5% to over 30% depending on the patient population and study.
The scope of digestive involvement extends beyond diarrhea, encompassing several other discomforts. Loss of appetite (anorexia) is often the most common gastrointestinal issue, reported by nearly 35% of patients. Nausea is also a frequent complaint, affecting over 25% of patients, and vomiting is reported in a smaller percentage. Abdominal pain is less common than these other symptoms, typically affecting less than 7% of patients.
How COVID-19 Affects the Digestive System
The reason the virus causes digestive distress lies in its cellular target, the ACE2 receptor. This receptor is highly expressed on the surface of enterocytes, the absorptive cells that line the small intestine. The concentration of ACE2 receptors in the small intestine is significantly higher than in the lungs.
When SARS-CoV-2 enters the body, it can infect these intestinal cells, leading to local inflammation and tissue damage. This direct viral invasion disrupts the normal function of the gut, causing increased fluid secretion and rapid movement of the intestines that results in diarrhea. The presence of the virus in the intestinal lining also explains why the genetic material of SARS-CoV-2 can be detected in stool samples.
Viral shedding, the release of virus particles, commonly occurs in the feces of infected individuals. This shedding can persist for a longer duration in the digestive tract than in the respiratory tract, with viral RNA sometimes detectable in stool even after nasopharyngeal swabs test negative. The detection of viral material in the stool has raised the possibility of a fecal-oral transmission route, though the primary mode of spread remains respiratory droplets.
When to Seek Testing or Medical Advice
Since diarrhea is a common symptom for many different illnesses, it is important to consider the context when deciding to seek testing for COVID-19. If new-onset diarrhea occurs alongside other common signs like fever, fatigue, headache, sore throat, or a loss of taste or smell, a COVID-19 test is strongly recommended. Testing is also advisable if you have had a known exposure to someone with the infection, even if only mild GI symptoms are present.
Most cases of COVID-related diarrhea are mild and resolve on their own, but certain symptoms warrant immediate medical attention. You should seek urgent care if you experience signs of severe dehydration, which can include dizziness, a rapid heart rate, or dark urine. Other concerning symptoms that require prompt evaluation are bloody or black, tarry stools, or severe, persistent abdominal pain. If diarrhea lasts longer than three to six days without improvement, consulting a healthcare provider is recommended.