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Gastrointestinal infections flashcards

10 high-yield MRCP Part 1 cards from the Intellect Medicos Infectious Diseases course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.

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1. Which organism causes vomiting within 1–6 hours of eating reheated fried rice?

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   Bacillus cereus.

   Why? A heat-stable preformed toxin (cereulide) causes rapid-onset vomiting.

2. What is the commonest cause of travellers' diarrhoea?

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   Enterotoxigenic E. coli (ETEC).

   Why? Its heat-labile toxin raises cAMP in enterocytes, causing watery diarrhoea.

3. Which neurological complication is classically triggered by Campylobacter jejuni?

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   Guillain–Barré syndrome.

   Why? Molecular mimicry between bacterial lipo-oligosaccharide and nerve gangliosides. Reactive arthritis can also follow.

4. Name two classic clinical clues to enteric (typhoid) fever.

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   Any two of: rose spots on the trunk, relative bradycardia, constipation early, abdominal pain, hepatosplenomegaly.

   Why? Salmonella typhi/paratyphi invades systemically; the major complication is intestinal perforation or GI bleed.

5. What is the first-line empirical treatment of enteric fever in a returning traveller from South Asia?

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   IV ceftriaxone (or oral azithromycin if uncomplicated).

   Why? Fluoroquinolone resistance is now widespread in South Asian isolates, so ciprofloxacin is no longer reliable empirically.

6. What is the first-line treatment for giardiasis?

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   Metronidazole (tinidazole is an alternative).

   Why? Giardia causes non-bloody, foul, fatty diarrhoea and bloating after travel or drinking untreated water; stool antigen confirms.

7. A man returns from India with fever, right upper quadrant pain and hepatomegaly. Ultrasound shows a liver abscess; aspirate looks like "anchovy sauce". What is the treatment?

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   Metronidazole, followed by a luminal amoebicide to clear gut cysts.

   Why? This is an amoebic liver abscess (Entamoeba histolytica). Metronidazole kills tissue trophozoites but not luminal cysts.

8. What does a jejunal biopsy show in Whipple's disease?

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   PAS-positive "foamy" macrophages in the lamina propria (with villous atrophy).

   Why? The macrophages are full of Tropheryma whipplei. PCR for T. whipplei supports the diagnosis.

9. How is Whipple's disease treated?

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   About 2 weeks of IV antibiotics (e.g. ceftriaxone or penicillin) then oral co-trimoxazole for about 1 year.

   Why? Long treatment is needed because relapse, especially in the CNS, is common.

10. Which stool stain shows Cryptosporidium oocysts?

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    Modified Ziehl–Neelsen (acid-fast) stain — red round oocysts on a blue-green background.

    Why? Cryptosporidium is an important cause of chronic watery diarrhoea in advanced HIV (CD4 <100); treatment is mainly restoring immunity with ART.