Green stool appearing during or after a COVID-19 infection can be surprising, but it occurs due to the virus’s effect on the digestive system. Although green stool is not a standard or highly reported symptom of COVID-19, the infection can trigger biological mechanisms that indirectly lead to this color change. Understanding the normal digestive process and how the virus interacts with the gut explains this observation.
Understanding Stool Color: The Role of Bile
The typical brown color of stool results from a process involving bile, a fluid produced by the liver. Bile is initially yellowish-green due to pigments like biliverdin and bilirubin, which are breakdown products of old red blood cells. Bile is secreted into the small intestine to aid in the digestion and absorption of fats.
As bile pigments travel through the intestines, gut bacteria chemically alter them. This metabolism converts the green pigments into stercobilin, which is responsible for the characteristic brown color of feces. This transformation requires sufficient time in the large intestine for bacterial action to complete. If transit time is shortened, pigment conversion is interrupted, and the green color persists.
COVID-19’s Impact on the Digestive System
The SARS-CoV-2 virus is recognized for its respiratory symptoms, but it also impacts the gastrointestinal (GI) tract. The virus enters human cells by binding to the angiotensin-converting enzyme 2 (ACE2) receptor, a protein highly expressed on intestinal cells. This abundance of ACE2 receptors makes the digestive system a direct target for viral infection.
Infection of the intestinal lining leads to inflammation and damage within the gut. This cellular disruption triggers common GI symptoms associated with COVID-19, including nausea, vomiting, abdominal pain, and diarrhea. Diarrhea is reported in a significant proportion of cases, sometimes affecting up to 30% of patients. This intestinal distress creates the conditions necessary for stool color changes.
Connecting the Dots: Rapid Transit and Green Stool
Green stool observed during a COVID-19 infection is a direct consequence of the rapid intestinal movement caused by the virus. When the SARS-CoV-2 infection induces inflammation in the intestines, it causes rapid transit. This means the bowel contents move through the digestive tract much faster than usual.
This quickened passage does not allow the naturally green bile sufficient time for metabolic conversion into the brown pigment stercobilin by gut bacteria. Consequently, the bile pigments retain their greenish hue, which is visible in the stool. While rapid transit driven by infection preserves the green color, green stool can also result from other factors. These include consuming large amounts of green vegetables high in chlorophyll, certain food colorings, or medications and supplements like iron.
When to Seek Medical Attention
Green stool is often a temporary side effect of digestive upset, but specific warning signs warrant medical consultation. If the green stool persists for more than a few days after COVID-19 symptoms have resolved, a healthcare professional should evaluate it. Severe or persistent diarrhea leading to signs of dehydration requires immediate medical attention, regardless of stool color.
Other concerning symptoms alongside green stool also signal a need for professional guidance. These include severe abdominal pain or cramping, a high fever, or vomiting lasting longer than 24 hours. Prompt medical care is also necessary if the stool contains blood, appearing bright red or tarry black, as this indicates bleeding in the gastrointestinal tract.