Infectious Colitis – Symptoms, Causes, Types and Treatment

What is Infectious Colitis?

Infectious colitis is inflammation of the colon (the main part of the large intestine) due to infection by bacteria, viruses, protozoa or fungi. It typically causes sudden lower abdominal pain/cramps and diarrhea. Infectious colitis, especially in food poisoning, is often associated with infection of the stomach and small intestine (gastroenteritis) which lie above and/or rectum (proctitis) which lie below the colon.

Colitis due to an infection is a common condition. It is often referred to as the stomach flu (viral) or stomach bug but the stomach is not always involved despite the names. Most of the time infectious colitis is acute. The symptoms are severe but resolves quickly with little to no treatment. Dehydration is always a risk. However, certain types of infectious diarrhea can be very severe and lead to profuse bloody diarrhea that can be fatal within a short period.

Symptoms of Infectious Colitis

Most of the time infectious colitis is acute. It arises suddenly, tends to cause severe symptoms and the infectious is often short-lived. However, in some cases the infection could be prolonged (sub-acute and rarely chronic) where the symptoms are ongoing for long periods of time and tends to be milder. All types of infectious colitis may cause:

  • Bloody or watery diarrhea (loose bowel movements), starting several hours to several days after start of an infection
  • Lower abdominal (stomach) pain or cramps
  • Constant urgency to have a bowel movement (the symptoms is medically known as tenesmus)
  • Pain in the rectum during bowel movement
  • Bloating (stomach distension due to accumulation of gas)
  • Fever
  • Nausea or vomiting

Causes of Infectious Colitis

Viruses, bacteria and protozoa are the main causes of infectious colitis. In rare cases, some fungi may also be responsible. Parasitic worms, also referred to as helminths or intestinal worms, cause an infestation of the human bowels and not an infection. Therefore human intestinal worms have not been discussed further.

The infectious agents below may either directly injure the lining and even deeper tissue of the colon wall, or it may indirectly injure the tissue through the action of its toxins. These agents may be spread through various different ways. Often it is transmitted by consuming food or water contaminated with these agents and/or its toxins.

Bacterial Colitis Due to Food Poisoning

Sudden, explosive diarrhea, appearing 12 to 72 hours after ingesting food contaminated with bacteria, like E.coli, shigella, salmonella, Yersinia or Campylobacter spp, is a characteristic symptom of bacterial intestinal infection. It is a common type of colitis.

E. coli is a common cause of traveller’s diarrhea. Shigella in developed parts of the world usually causes a mild, self-limiting disease (shigellosis), but in poor areas it may cause a severe, often deadly infection known as bacillary dysentery.

Bacteria like Cholerae vibrio cause cholera which can cause profuse watery diarrhea. Often this diarrhea has a white color and resembles rice water. Cholera is a common and potentially deadly form of infectious colitis, especially when dehydration is not treated and managed properly.

Parasitic Colitis Due to Protozoa

Insidious, slowly developing diarrhea with mucus and abdominal bloating starting several days or weeks after ingesting food contaminated with protozoa, is characteristic for parasitic colitis. The most often cause of parasitic colitis is a one-cell parasite Entameba hystolytica, mainly transmitted by contaminated water and resulting in a mild or severe, often fatal infection, known as amebic dysentery.

Pseudomembranous Colitis – Cl. Difficile Overgrowth After Antibiotics

Bacterium Clostridium difficile is commonly present in the colon as the part of the normal intestinal flora, but its growth is limited by growth of other “healthy” bacteria. When these healthy bacteria are destroyed by antibiotics taken by mouth (like amoxicillin and clindamycin), Clostridium difficile may overgrow and excrete toxins that cause inflammation of the colon known as pseudomembranous colitis. Watery diarrhea, lower left abdominal pain or bloating and barnyard smell of gas and stool, and fever are main symptoms.

Viral Colitis

Viral colitis can be due to several viruses that may also infect the small intestine and even the stomach. This is sometimes referred to as the stomach flu, although the term can be misleading since the influenza group of viruses are not involved.

Cytomegalovirus (CMV) may cause colitis in persons with lower immunity (due to chemotherapy, HIV/AIDS and so on). Herpetic colitis, caused by Herpes simplex virus (HSV) mostly occurs in homosexual men and is usually acquired during anal intercourse.

Fungal Colitis

Colitis caused by fungi, like Candida albicans or other fungal species, is rare. It mainly occurs in persons with lowered immunity, particularly in HIV/AIDS.

Diagnosis of Infectious Colitis

Diagnosis of infectious colitis may be suspected from the history of bloody diarrhea with urgency, appearing several hours after a suspicious meal, especially if other persons that have eaten the same food were also affected.


  • Bacteria can be detected by stool culture.
  • Parasites can be detected by “Ova and Parasites” (O&P) test of the stool, which is often false negative, so sometimes several repeating tests are needed if parasites are still suspected.
  • Blood tests. Elevated white cells in the blood speak for presence of inflammation anywhere in the body but do not by themselves confirm infection of the colon. Increased eosinophils(special type of white cells) and IgE antibodies are regularly elevated in parasitic infection. Microbes, appearing in the blood (sepsis) of a patient with bloody diarrhea, speak for invasive colitis.

Other causes of left side abdominal pain, especially diverticulitis, or right side abdominal pain, like a flare of Crohn’s colitis, and causes of the blood in the stool, and acute (sudden) diarrhea have to be considered.

Treatment of Infectious Colitis

Infectious colitis is treated by antibiotics or anti-parasitic medications, prescribed on the basis of results of stool tests. Viral infections usually do not require specific treatment to eradicate the infection and will resolve spontaneously with time. Rehydration solutions are needed to replace lost water and minerals. Pain killers and drugs to lower high fever (antipyretic agents) may be needed in severe infection. Iron may need to be replaced in severe or prolonged bleeding.

Related articles:

Bacterial Diarrhea Due to Food Poisoning
Human Intestinal Parasites

About Jan Modric (209 Articles)
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