Infectious Colitis

Causes

Bacteria

Viruses

• cytomegalovirus (CMV), mainly in people with weakened immunity or inflammatory bowel disease
• norovirus and others usually cause gastroenteritis rather than colitis

Parasites

• Entamoeba histolytica (amoebic dysentery), after travel to areas with poor sanitation
• others such as Schistosoma in endemic areas

Symptoms

• diarrhea, often frequent and small in volume
• blood or mucus in stool
• belly cramps, usually in the lower belly
• urgency and tenesmus (a constant feeling of needing to pass stool)
• fever and chills
• nausea, vomiting
• dehydration

Infectious colitis vs inflammatory bowel disease

Infectious colitis usually starts suddenly and settles within days to 2 weeks. Ulcerative colitis and Crohn's disease tend to develop over weeks, recur, and do not resolve on their own. A first flare of inflammatory bowel disease can look identical, so stool tests are needed. Infections can also trigger flares in people with known IBD.

Other look-alikes include ischemic colitis, diverticulitis and medication-induced colitis.

Diagnosis

• Stool tests: multiplex PCR panels identify many bacteria, viruses and parasites at once; stool culture; Shiga toxin testing; C. difficile toxin or PCR testing
• Blood tests: blood count, kidney function, electrolytes, and inflammatory markers; blood cultures if very unwell
• Imaging: CT if there is severe pain or concern for complications
• Colonoscopy or sigmoidoscopy: for persistent symptoms, suspected CMV, or to distinguish from IBD

Treatment

Rehydration

The most important treatment. Oral rehydration solutions are best for mild to moderate dehydration; IV fluids for severe dehydration or vomiting.

Antibiotics

Antibiotics are not needed for most mild infectious diarrhea and can cause harm. They are used for:

• severe illness, high fever or sepsis
• Shigella, and some Campylobacter cases
• people at high risk: older adults, weakened immunity, prosthetic heart valves
• C. difficile (fidaxomicin or oral vancomycin)
• amoebic colitis (metronidazole followed by a luminal agent)

Antibiotics are avoided for suspected STEC E. coli because they may increase the risk of hemolytic uremic syndrome.

Symptom relief

• Avoid antidiarrheal medicines such as loperamide with bloody diarrhea or high fever, unless advised by a clinician.
• Eat as tolerated; bland foods are fine.
• Acetaminophen (paracetamol) for fever and pain, following the label dose.

Complications

• dehydration and kidney injury
• hemolytic uremic syndrome after STEC
• toxic megacolon or perforation in severe C. difficile colitis
• reactive arthritis and Guillain-Barré syndrome after some bacterial infections
• post-infectious irritable bowel syndrome

Prevention

• wash hands after using the toilet, changing diapers and handling raw meat or animals
• cook poultry and ground beef thoroughly
• avoid unpasteurized milk and juices
• wash produce
• use antibiotics only when needed to reduce C. difficile risk
• follow safe food and water precautions when traveling

Frequently asked questions

What causes infectious colitis?

Most cases are caused by bacteria such as Campylobacter, Salmonella, Shigella, Shiga toxin-producing E. coli and C. difficile. Viruses such as CMV and parasites such as Entamoeba histolytica are less common causes.

How long does infectious colitis last?

Most cases improve within a few days to a week, and nearly all resolve within 2 weeks. C. difficile colitis may need longer treatment and can recur. Symptoms lasting more than 2 weeks should be investigated further.

Is infectious colitis contagious?

Yes. Most causes spread through the fecal-oral route: contaminated food or water, or hands that have not been washed after using the toilet. Good handwashing and staying home while you have diarrhea help prevent spread.

Do you need antibiotics for infectious colitis?

Not usually. Most mild cases clear on their own with fluids. Antibiotics are used for severe illness, certain organisms like Shigella and C. difficile, and high-risk people. They are avoided for STEC E. coli because they can increase complications.