Colitis is inflammation of the colon, the large intestine, caused by various factors including infections, autoimmune responses, or reduced blood flow. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19, primarily targets the respiratory system but affects multiple other organs. Research suggests a connection between SARS-CoV-2 infection and the onset or exacerbation of colon inflammation. Understanding this relationship is crucial for diagnosing and managing post-viral complications.
How COVID-19 Affects the Gastrointestinal Tract
The SARS-CoV-2 virus is a systemic pathogen, not strictly limited to the lungs. The virus gains entry into human cells by binding to the Angiotensin-Converting Enzyme 2 (ACE2) receptor. This receptor is highly expressed on epithelial cells lining the entire gastrointestinal tract, particularly in the small intestine and colon.
The high concentration of ACE2 receptors allows the virus to infect and replicate within the digestive system. This explains the prevalence of gastrointestinal symptoms in acute COVID-19 infection, such as nausea, vomiting, and diarrhea. The presence of viral RNA in fecal samples long after respiratory symptoms have cleared further confirms the gut as a site of infection and replication, setting the stage for complications like colitis.
Clinical Evidence Linking COVID-19 and Colitis
Observational studies and case reports have documented colitis following or during SARS-CoV-2 infection. This clinical evidence falls into two categories: new-onset colitis and the triggering of flare-ups in individuals with pre-existing conditions. This complication is a documented extra-pulmonary manifestation of the disease.
The virus has been linked to de novo colitis, meaning inflammation occurring in a patient with no prior history. Case reports identify new diagnoses of ulcerative colitis, a type of Inflammatory Bowel Disease (IBD), developing shortly after recovery. Acute hemorrhagic colitis, characterized by severe inflammation and bleeding, has also been reported where SARS-CoV-2 viral protein was detected directly in the colon tissue.
COVID-19 also triggers relapse in patients already diagnosed with IBD, such as ulcerative colitis and Crohn’s disease. The systemic stress and inflammation disrupt the immune system, leading to a flare-up of the underlying disease. Another presentation is ischemic colitis, inflammation caused by inadequate blood flow to the colon. This is attributed to the hypercoagulable state—an increased tendency for blood clotting—that is a known feature of severe COVID-19.
Symptoms and Medical Evaluation
Colitis symptoms warrant prompt medical attention and are distinct from the mild diarrhea seen in acute infection. A patient may experience persistent, watery diarrhea that often becomes bloody (hematochezia). This is frequently accompanied by severe abdominal pain, tenderness, and cramping, especially in the lower abdomen.
The medical evaluation differentiates COVID-19-associated colitis from other common causes of colon inflammation. Physicians order blood work to check for elevated inflammatory markers, such as C-reactive protein (CRP), and D-dimer, which can indicate blood clots suggesting an ischemic cause. Stool testing is crucial to rule out infectious causes like Clostridioides difficile or other bacterial and viral pathogens.
If symptoms are severe or persistent, imaging like a CT scan or an endoscopic procedure may be necessary. Colonoscopy allows a gastroenterologist to visualize the inflamed colon lining and take biopsies. Tissue samples confirm the diagnosis of colitis and may be tested to detect SARS-CoV-2 viral components within the colon cells, confirming a direct viral cause.
Potential Biological Mechanisms
The pathway by which SARS-CoV-2 infection leads to colon inflammation involves a combination of three main biological mechanisms. The first is the systemic hyper-inflammation that characterizes severe COVID-19, often referred to as a “cytokine storm.” The widespread release of pro-inflammatory molecules, such as interleukins, can cause collateral damage to the intestinal lining and trigger an autoimmune-like response.
Another proposed mechanism is the development of gut dysbiosis, an imbalance in the gut microbiome. SARS-CoV-2 infection alters the composition of gut bacteria, often depleting beneficial microbes and increasing opportunistic pathogens. This microbial imbalance compromises the integrity of the intestinal barrier, promoting chronic inflammation and potentially contributing to IBD-like symptoms.
Finally, the hypercoagulable state frequently seen in COVID-19 patients can lead to direct vascular injury in the colon. The formation of micro-clots in the small blood vessels supplying the intestinal wall restricts blood flow. This lack of oxygen and nutrients causes tissue damage and death, resulting in ischemic colitis.