Investigations
1st investigations to order
stool culture and sensitivity
Test
Use stool culture and sensitivity kit.
Diarrhoeal stool is the preferred specimen over formed stool or swab to detect diarrhoeal illness, except in children where swab is acceptable when there is sufficient faeces on the swab.[30]
Stool cultures usually take a longer time to process and may fail to detect the causative agent.[30] Negative stool work-ups are very likely, and in the acute TD clinical scenario, a course of empirical therapy should be tried.
Not necessary for non-severe TD or if traveller has not tried a course of appropriate antibiotic therapy.
Result
identifies specific bacterial aetiology with sensitivities
multi-pathogen molecular diagnostic (polymerase chain reaction)
protozoal stool antigens
Test
Performed for persistent diarrhoea (usually >14 days).
Reagents are commercially available for Cryptosporidium species, Entamoeba histolytica, and Giardia duodenalis.
Result
identifies Giardia, Cryptosporidium, E histolytica
Investigations to consider
stool ova and parasite examination
Test
Performed for persistent diarrhoea (usually >14 days). The Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM) guidelines suggest considering testing for parasites in patients having persistent diarrhoea for >7 days.[30]
Use stool ova and parasite (O+P) collection kit.
Cryptosporidium is easily missed on stool O+P.
Cryptosporidium stool antigen test is specific for this organism.
Not as reliable as stool antigen test for detection of Giardia.
Result
identifies specific parasitic aetiology (a negative acid-fast stain helps to exclude Cryptosporidium and Cyclospora)
Clostridioides difficile stool toxin
Test
Recommended in the scenario of inflammatory colitis in a returning traveller with recent antibiotic exposure.
Result
identifies C difficile
colonoscopy, endoscopy, and biopsy
Test
Recommended for chronic diarrhoea to rule out structural or organic disease.
Result
identifies inflammatory bowel disease, colon cancer, microscopic colitis, tropical sprue and malabsorptive conditions, and coeliac disease
haematology, blood chemistries, serology
Test
C-reactive protein, erythrocyte sedimentation rate, and liver function tests identify organic disease.
White blood cells, and particularly eosinophilia, are indicative of extra-intestinal protozoa (e.g., Strongyloides).
Coeliac serologies considered depending on traveller family history and symptoms.[6]
Result
test based on individually derived differential diagnosis
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