What is Infectious Colitis?
Infectious colitis specifically describes the inflammation of the large intestine, known as the colon, brought on by an invasion of pathogenic microbes. These organisms, which can be bacteria, viruses, or parasites, directly attack the mucosal lining of the colon. This assault compromises the colon’s fundamental function: the absorption of water and electrolytes from digested material. Instead of drawing water out, the inflamed and damaged intestinal wall leaks fluid, mucus, and sometimes blood into the colon’s interior. This process results in the characteristic symptoms of acute diarrhea, abdominal pain, and urgency associated with the condition.
Causes:Infectious colitis is initiated when a sufficient quantity of a pathogenic microbe successfully reaches the large intestine and overwhelms the body's local defenses. This is most commonly achieved through a breakdown in sanitation or hygiene, leading to ingestion of the pathogen. The primary causal pathways are:
- Ingestion of Contaminated Foodstuffs: This occurs when food is tainted with pathogenic bacteria, such as Salmonella, Campylobacter, or E. coli. The contamination can happen at the source (e.g., raw poultry) or during preparation by an infected food handler. If the food is not cooked to a temperature high enough to kill the microbes, they are consumed, survive passage through the stomach's acid, and then establish an infection by directly colonizing and attacking the mucosal lining of the colon.
- Direct Fecal-Oral Transmission: Highly contagious viruses like Norovirus or bacteria such as Shigella spread efficiently from person to person. An infected individual sheds massive quantities of the pathogen in their stool. If they fail to wash their hands properly, microscopic particles can be transferred to surfaces, objects, or directly to another person's hands. The new host becomes infected when they subsequently touch their mouth, ingesting the pathogen.
- Disruption of the Colon's Natural Microbiota: Sometimes, the cause is an internal imbalance rather than an external invasion. The use of broad-spectrum antibiotics can indiscriminately eliminate the beneficial, protective bacteria that normally reside in the colon. This creates a biological void, allowing opportunistic, toxin-producing bacteria like Clostridioides difficile (C. diff), which may be present in small, harmless numbers, to multiply without competition. These overgrown bacteria then release powerful toxins that directly damage the colon wall, causing severe inflammation.
While anyone can experience infectious colitis, the probability of developing a severe infection is notably higher in individuals with specific vulnerabilities related to their age, immune function, or recent medical history. The following groups are more susceptible:
- Individuals at the Extremes of the Age Spectrum: The very young and the elderly share a heightened vulnerability to this condition. The still-developing immune systems of young children are less experienced in fighting off these pathogens, while the immune responses of older adults are often less vigorous, making both groups less capable of preventing an infection from taking hold.
- People with Impaired Immune Defenses: Anyone with a significantly weakened immune system faces an increased likelihood of infection. This includes individuals taking immunosuppressive drugs after an organ transplant, those with advanced HIV, or patients undergoing cancer chemotherapy, as their bodies lack the robust cellular army needed to effectively eliminate the invading microbes from the colon.
- Patients with Recent Antibiotic Exposure: Individuals who have recently completed a course of broad-spectrum antibiotics are uniquely susceptible, particularly to Clostridioides difficile colitis. The antibiotic treatment can decimate the protective community of normal gut bacteria, creating a biological vacuum that allows toxin-producing bacteria to proliferate without competition.
- Those with Reduced Stomach Acidity: People who regularly use medications that suppress the production of stomach acid, such as proton pump inhibitors (PPIs), have a greater susceptibility. Stomach acid serves as a critical first-line defense by killing many ingested pathogens; when this chemical barrier is reduced, a larger number of microbes are able to survive their passage to the colon and initiate an infection.
