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Colitis is the medical term that describes inflammation of the colon, or large intestine. Infectious colitis is inflammation of the colon caused by an infectious agent. These include bacteria, viruses and parasites. Infectious colitis is usually a self-resolving condition, but it can be complicated by the symptoms of diarrhea, dehydration and bleeding.


According to MayoClinic.com, there are several infectious agents that can cause infectious colitis. Viruses such as rotavirus, the most common cause of childhood diarrhea, Norwalk virus and cytomegalovirus commonly cause this condition. Bacterial colitis is caused by ingestion of contaminated food products, like uncooked meat or chicken and improperly processed bacteria. Common bacteria include Escherichia coli, salmonella, campylobacter and Shigella. Parasites can also cause colitis, in specific Giardia lamblia and cryptosporidium.


The main symptoms of infectious colitis include diarrhea, fever, dehydration and blood in the stool. According to the Merck Manual for Healthcare Professionals, the stools become watery and can have blood and mucous in them. The infectious microbe also produces a large amount of gas, causing intestinal distension, cramps, bloating and the feeling of having to stool frequently, called tenesmus.


The frequency of the diarrhea and the occasional accompanying nausea and vomiting can lead to dehydration. Symptoms of dehydration include decreased urine output, rapid heart rate as the heart tries to compensate for the decrease in fluid by pumping more blood, and dry lips and mucous membranes. Occasionally, the severity of rectal bleeding makes the patient anemic and in need of a blood transfusion. This is especially true in people who develop hemolytic-uremic syndrome, a complication that, according to the CDC, occurs in about 8% of people infected with enterohemorrhagic Escherichia coli. Hemolytic-uremic syndrome causes kidney failure and hemolytic anemia, or loss of red blood cells.


Identifying the microbe causing the infection is important in determining if treatment is available and in limiting the spread of the infection. For example, a case of Escherichia coli infection might prompt an investigation into whether a food product may be contaminated. Infection with parasites may prompt limiting access to a body of water, like a lake or a pond, where those microbes are usually found.


The treatment of infectious colitis is usually supportive, with fluids given either orally or intravenously to treat dehydration, and medicines for fever and pain control. Antibiotics may help treat some bacterial colitis, especially if the person is critically ill, and parasitical infections. Viral colitis does not respond to antibiotics. Anti-diarrheal agents may work in mild diarrhea, but in severe diarrhea use of these medications must be closely monitored, as they can slow down the intestinal motility and cause toxic megacolon, a potentially dangerous complication.