What is the appropriate diagnostic workup and treatment for a patient with a 3-month history of bloody diarrhea, who recently traveled to another country?

Diagnostic Workup for Chronic Bloody Diarrhea After International Travel

For a patient with 3 months of bloody diarrhea after international travel, you must obtain stool studies for bacterial culture (Salmonella, Shigella, Campylobacter), ova and parasites with specific testing for Entamoeba histolytica, complete blood count with differential to assess for eosinophilia, and consider serologic testing for Strongyloides if travel was to endemic regions. 1

Initial Laboratory Testing

Stool Studies (Priority Testing)

• Bacterial culture for Salmonella, Shigella, and Campylobacter on a single stool sample 1, 2
• Ova and parasites examination with at least 3 separate stool specimens to increase sensitivity beyond 80% 1
• Specific testing for Entamoeba histolytica using immunofluorescence or enzyme immunoassay, as amoebic colitis causes bloody diarrhea with indolent onset and is a critical diagnosis in returning travelers 1
• Wet preparation of freshly passed stool (within 15-30 minutes) to identify amoebic trophozoites if amoebic dysentery is suspected 1

Blood Work

• Complete blood count with differential to identify eosinophilia, which suggests parasitic infection including Strongyloides, Schistosoma, or other helminths 1
• Blood cultures if fever is present or sepsis is suspected 1, 3

Additional Testing Based on Travel History and Clinical Features

Parasitic Evaluation

• Strongyloides serology should be obtained for long-term travelers returning from endemic areas (Southeast Asia, sub-Saharan Africa, Latin America), even without symptoms or eosinophilia, as this parasite can cause life-threatening hyperinfection in immunosuppressed patients 1
• Schistosomiasis testing if there was freshwater exposure, particularly if eosinophilia is present 3
• Multiple stool examinations may be needed for Strongyloides as single stool sensitivity is low 1

Molecular and Advanced Testing

• Molecular testing aimed at a broad range of clinically relevant pathogens is preferred when rapid results are needed or conventional tests fail to establish diagnosis 1
• Shiga toxin testing (STEC O157 and other STEC) should be included, though antibiotics must be avoided if positive 1, 2

Critical Diagnostic Considerations for Persistent Symptoms

When Symptoms Last >14 Days

• Microbiologic testing is mandatory in returning travelers with persistent symptoms or those who fail empiric therapy 1
• Consider non-infectious etiologies including:
  • Post-infectious irritable bowel syndrome (PI-IBS), which commonly occurs after traveler's diarrhea 1, 4
  • Inflammatory bowel disease (IBD), which can be unmasked by acute infectious diarrhea 1
  • Lactose intolerance or disaccharidase deficiency 1, 4

Geographic-Specific Pathogens

• Travel destination determines pathogen likelihood: Campylobacter resistance to fluoroquinolones exceeds 85% in Southeast Asia, making this information critical for treatment decisions 5, 3
• Enteric fever (typhoid/paratyphoid) should be considered with prolonged fever and abdominal symptoms 1, 3

Laboratory Safety Precautions

Alert the laboratory when submitting specimens if you suspect enteric fever, brucella, Q fever, melioidosis, or viral hemorrhagic fevers, as these require upgraded infection control procedures to protect laboratory staff 1

Imaging and Endoscopy

• Flexible colonoscopy with biopsy is useful to differentiate bacterial hemorrhagic enterocolitis from inflammatory bowel disease or ischemic colitis, particularly when initial testing is unrevealing 6
• Abdominal ultrasound if right upper quadrant pain is present to evaluate for amoebic liver abscess 3

Common Pitfalls to Avoid

• Do not assume acute bacterial infection after 3 months of symptoms—parasitic causes, particularly Entamoeba histolytica and Giardia, become more likely with persistent diarrhea 1, 4
• Do not rely on single stool examination for parasites—sensitivity increases substantially with multiple specimens 1
• Do not overlook eosinophilia, which is a critical clue to helminthic infection requiring specific serologic testing 1
• Do not forget Strongyloides screening in endemic area travelers, as this can remain dormant and cause fatal hyperinfection years later 1