Acute bloody diarrhoea: identifying the organism

What it is

Acute diarrhoea is split first by whether there is blood in it and by whether there are WBC in stool, and bloody diarrhoea with fever and crampy abdominal pain is dysentery. The short list of causative agents for the bloody half is Salmonella, Shigella, Yersinia, E. coli 0157:H7 and Campylobacter, to which Entamoeba histolytica is added when there is a history of travel. Where there is no blood the agents named are S. aureus, B. cereus, Giardia, cryptosporidium and viral causes. The most common agent causing food poisoning is Campylobacter.

How it presents

Each species carries its own onset and its own clue in the history.

• Salmonella: 6-72 hours, with fecal leukocytosis. Exposure to animals (poultry, turtles, petting zoos), and eggs and fish.
• Shigella: 1-3 days, with tenesmus and fecal leukocytosis, after raw vegetables. It is the most common cause of acute bloody diarrhoea.
• Campylobacter jejuni: 1-7 days. A flu-like prodrome is usually followed by crampy abdominal pains, fever and diarrhoea which may be bloody. Consumption of undercooked meat.
• E. coli 0157:H7: painful bloody diarrhoea, from undercooked hamburger meat.
• Entamoeba histolytica: 1-11 weeks, so more than a week from the exposure, with a history of travel.

Amebic dysentery is the most common presentation of Entamoeba histolytica, a protozoan parasite transmitted through the faeco-oral route with the ingestion of viable protozoal cysts.