Differentials
Bacterial gastroenteritis
SIGNS / SYMPTOMS
High fever, bloody diarrhoea, or severe diarrhoea suggests bacterial infection.
INVESTIGATIONS
Stool microscopy and culture are differentiating tests. Evidence of inflammation (faecal leukocytes or a positive lactoferrin immunoassay) may be present. Culture may grow enteropathogenic bacteria, such as Campylobacter jejuni, Salmonella species, enteropathogenic Escherichia coli, Shigella, Yersinia enterocolitica, Shiga toxin-producing E coli, or Vibrio cholerae.
Protozoal infections
SIGNS / SYMPTOMS
May be suspected if a patient has recently travelled to countries where protozoal infections are endemic (e.g., Mexico, India, South America, many parts of the US). Signs and symptoms vary based on the parasite.
Amoebic dysentery presents with bloody diarrhoea with excessive mucus and abdominal pain.
Giardiasis can present with bloating and prolonged diarrhoea.
Parasitic infections should always be ruled out in immunocompromised patients.
INVESTIGATIONS
Traditionally, stool microscopy is used to identify Giardia lamblia, Entamoeba histolytica, cryptosporidium, or other parasites. Stool antigen testing or serology can also be used.
Helminthic infections
SIGNS / SYMPTOMS
These infections are common in immunocompromised patients and in immigrants from endemic areas.
INVESTIGATIONS
Stool microscopy can identify the worm.
Clostridium difficile colitis
SIGNS / SYMPTOMS
Recent antibiotic use is a risk factor.
Some cases can progress very rapidly to serious toxic megacolon, so early detection and presumptive treatment with oral metronidazole or vancomycin may be warranted.
INVESTIGATIONS
Stool test for C difficile toxin would be positive.
Food poisoning
SIGNS / SYMPTOMS
Usually suspected if multiple people develop symptoms after eating the same contaminated food or drink. Symptoms can vary from nausea, vomiting, abdominal pain, and/or diarrhoea, which start suddenly a few hours to 2 days after eating the contaminated food.
INVESTIGATIONS
Stool cultures are low-yield as most of these diseases are caused by toxins. Toxin testing may be available for epidemiological purposes.
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