Differentials
Non-Shigella bacterial diarrhea
SIGNS / SYMPTOMS
It is often not easy to differentiate between pathogens that cause bloody diarrhea, as diagnostic yields in diarrheal stool samples are reported to be low.[29]
Bloody diarrhea is suspicious for Shigella or enterohemorrhagic Escherichia coli.
Other bacterial infections such as Campylobacter jejuni, Vibrio cholerae, Yersinia enterocolitica, and Salmonella may also cause bloody diarrhea.[5]
Watery diarrhea often occurs with V cholerae.
Clostridium difficile may rarely cause bloody diarrhea. If risk factors such as previous antibiotic therapy or exposure are present, C difficile should be considered.
INVESTIGATIONS
Stool cultures are useful to differentiate bacterial causes of diarrhea.
Viral gastroenteritis
SIGNS / SYMPTOMS
Viral causes of diarrhea (such as norovirus, adenovirus, and rotavirus) do not usually cause bloody diarrhea. In addition, vomiting tends to be a significant feature of these infections.[5]
INVESTIGATIONS
Negative stool microscopy and culture along with clinical suspicion.
Parasitic diarrhea
SIGNS / SYMPTOMS
In low- and middle-income countries, Entamoeba histolytica, Giardia intestinalis, Cryptosporidium parvum, and Cyclospora cayetanensis commonly cause diarrheal disease.[5]
Parasitic diarrhea in the high-income countries world is uncommon and may be related to exposure during travel.
Except in E histolytica infection, diarrhea is not usually bloody.
INVESTIGATIONS
Stool microscopy is useful to detect parasites.
Idiopathic inflammatory bowel disease
SIGNS / SYMPTOMS
The course of idiopathic inflammatory bowel disease (Crohn disease, ulcerative colitis, microscopic colitis) is often more protracted than that of shigellosis.[26] There may be a history or family history of the disease. Extra-intestinal manifestations of idiopathic inflammatory bowel disease may be present (e.g., skin lesions or fistulae).
INVESTIGATIONS
Negative stool cultures and positive sigmoidoscopy findings suggest inflammatory bowel disease.
Celiac disease
SIGNS / SYMPTOMS
Persistent (>14 days) diarrhea may prompt consideration of celiac disease. However, the diarrhea is not bloody.
INVESTIGATIONS
Positive celiac serology is diagnostic. If there is clinical suspicion, duodenal biopsy may be indicated after a gluten challenge.
Malignancy
SIGNS / SYMPTOMS
May present with change in bowel habits, usually with loose stools.
There may be a history of anorexia or weight loss. Patients are usually >45 years old.
INVESTIGATIONS
Abnormal colonoscopy and evidence of a tumor or metastatic disease on CT studies characterize malignancy.
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