Gastrointestinal Infections and Tropical Diseases
This domain tests pattern recognition in endemic and imported infection, with emphasis on diseases that remain common in Egypt and the region.
Diarrheal infection
- Acute watery diarrhea is usually viral or toxin-mediated; invasive diarrhea (blood, fever, tenesmus) suggests Shigella, Campylobacter, Salmonella, enteroinvasive E. coli or Entamoeba histolytica. Stool culture, PCR and microscopy guide therapy.
- Clostridioides difficile: test with toxin or nucleic acid amplification in symptomatic patients; stop the inciting antibiotic; first episode treated with oral vancomycin or fidaxomicin; recurrent disease may need fecal microbiota transplantation.
- Amebic liver abscess: right upper quadrant pain, fever, raised alkaline phosphatase; serology positive; metronidazole followed by a luminal agent such as paromomycin or diloxanide.
- Giardiasis: bloating, steatorrhea; stool antigen or PCR; tinidazole or metronidazole.
Helminths and tropical disease
- Schistosoma mansoni causes periportal fibrosis and presinusoidal portal hypertension; S. haematobium causes hematuria and bladder squamous carcinoma. Diagnose with urine or stool microscopy and serology; treat with praziquantel.
- Fasciola hepatica: biliary colic, eosinophilia, liver lesions; treat with triclabendazole.
- Ascariasis may cause biliary obstruction or intestinal obstruction; treat with albendazole or mebendazole.
- Hookworm causes iron deficiency anemia; Strongyloides can cause hyperinfection with corticosteroids; ivermectin is the treatment.
- Hydatid cyst (Echinococcus granulosus): avoid aspiration without precautions due to anaphylaxis risk; albendazole with PAIR or surgery.
Tuberculosis and other regional issues
- Abdominal tuberculosis mimics Crohn disease: ascites with SAAG below 1.1 g/dL, high ADA, caseating granulomas, and sometimes terminal ileal involvement. Treat with standard antituberculous therapy.
- Brucellosis causes fever, hepatosplenomegaly and sacroiliitis; doxycycline plus rifampicin or streptomycin.
- Typhoid fever: stepwise fever, relative bradycardia, rose spots; blood culture; treat with ceftriaxone or azithromycin depending on resistance.
Worked example
A 40-year-old farmer has fever, right upper quadrant pain, eosinophilia and a hypoechoic liver lesion with a track to the bile duct. Consider fascioliasis and treat with triclabendazole rather than draining as a pyogenic abscess.
Traps
- Treating amebic abscess with metronidazole alone without a luminal agent.
- Using corticosteroids in Strongyloides infection without ivermectin cover.
- Diagnosing Crohn disease without excluding intestinal tuberculosis in endemic areas.
- Missing schistosomal periportal fibrosis as a cause of variceal bleeding.