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MI4.1-9 | Gastrointestinal & Hepatobiliary Infections — Graded Quiz
Graded
12 questions · Untimed · 2 attempts
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A 30-year-old man presents with 2 days of bloody mucoid stools, tenesmus, and fever. Stool microscopy shows sheets of PMNs and RBCs; no cysts or trophozoites are seen. Stool culture on DCA agar shows non-lactose-fermenting, non-H₂S-producing colonies. Tube agglutination confirms the organism. Which pathogenesis best explains the fever and bloody stool in this case?
A
Preformed enterotoxin absorbed from food stimulates cAMP
B
Invasion of colonic epithelium triggers intense PMN-mediated inflammatory response
✓
C
Microaerophilic organism penetrates gastric mucosa causing systemic bacteraemia
D
Attachment to duodenal microvilli inhibits absorption without mucosal invasion
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A laboratory receives a stool sample from a 25-year-old with suspected amoebic dysentery. The fresh stool is examined: trophozoites are seen but RBCs are absent within them. The attending clinician says the patient has bloody stools. What is the most appropriate next step in diagnosis?
A
Report as Entamoeba histolytica; treatment can begin
B
Consider Entamoeba dispar; add stool antigen ELISA or PCR to confirm E. histolytica
✓
C
Repeat culture on TCBS agar to rule out Vibrio co-infection
D
Perform CLO test on the biopsy to confirm H. pylori gastritis
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A cluster of 8 college students develop watery diarrhoea and vomiting 18 hours after eating fried rice from a canteen that had been kept warm for several hours. Three have fever. The diarrhoea is described as profuse and watery. Which organism and toxin type best explains this presentation?
A
Staphylococcus aureus; heat-stable enterotoxin, 2-hour incubation
B
Bacillus cereus; heat-labile diarrhoeal toxin (HBL/NHE), 8–16-hour incubation
✓
C
Bacillus cereus; heat-stable cereulide (emetic toxin), 1–5-hour incubation
D
Clostridium perfringens type A; alpha-toxin causing gas gangrene
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Which ONE statement correctly describes the difference between invasive and non-invasive diagnostic tests for Helicobacter pylori, particularly relevant to monitoring eradication success?
A
Serology (IgG ELISA) is the preferred test to confirm eradication 4 weeks post-treatment
B
Urea breath test (UBT) is the preferred non-invasive test to confirm eradication, performed ≥4 weeks post-treatment
✓
C
Histopathology of antral biopsy is superior to UBT for routine eradication monitoring
D
Rapid urease test (CLO test) is recommended for eradication monitoring as it does not require endoscopy
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A 28-year-old blood bank technician is incidentally found to have: HBsAg positive (>6 months), HBeAg negative, anti-HBe positive, HBV DNA 300,000 IU/mL. ALT is mildly elevated. What is the most accurate interpretation?
A
Immune-tolerant phase: high viral load, normal ALT, no liver damage
B
HBeAg-negative chronic hepatitis B with active viral replication (pre-core mutant)
✓
C
Inactive carrier state: HBeAg negative, low viral load, normal ALT
D
Window period of acute HBV: anti-HBs absent, anti-HBc IgM present
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During a cholera outbreak investigation, field samples are transported in alkaline peptone water (APW) rather than standard transport medium. What is the purpose of using APW for Vibrio cholerae transport?
A
APW reduces contamination by killing all enteric bacteria at high pH
B
APW enriches Vibrio cholerae selectively, as it thrives at alkaline pH while most gut commensals do not
✓
C
APW preserves the heat-labile cholera toxin during transport for ELISA testing
D
APW provides a neutral buffered environment preventing cell lysis by osmotic stress
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A 35-year-old healthcare worker receives the hepatitis B vaccine series and is tested 6 weeks after the third dose. Results: anti-HBs 8 mIU/mL, anti-HBc negative. She works in a high-risk unit. What is the most appropriate action?
A
She is adequately protected; no further action needed
B
Repeat the three-dose primary series and recheck anti-HBs; if still <10 mIU/mL, test for HBsAg
✓
C
Give one booster dose; recheck anti-HBs in 4 weeks
D
Administer hepatitis B immune globulin (HBIG) immediately as primary vaccination has failed
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A 4-year-old presents with 5 days of high fever, then develops jaundice. Liver enzymes: AST 1200 U/L, ALT 1500 U/L. Anti-HAV IgM positive. Parents report the child attended a birthday party 4 weeks ago where several other children later developed jaundice. Which HAV virological feature explains the high stool shedding during the prodrome (before jaundice appears)?
A
HAV integrates into hepatocyte DNA during prodrome, enabling high-level virion production
B
HAV replicates in hepatocytes, is excreted in bile, and shed in stool at peak levels before ALT rises
✓
C
HAV viraemia during prodrome is the primary route of faecal shedding via glomerular filtration
D
HAV exists only in cyst form in the intestine during the prodrome, protected from immune clearance
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Why does Hepatitis D virus (HDV) require co-infection or superinfection with Hepatitis B virus (HBV) to establish a productive infection?
A
HDV uses HBV's RNA polymerase for replication of its own RNA genome
B
HDV uses HBsAg as its outer envelope for assembly and cell exit
✓
C
HDV requires HBcAg to package its ribonucleoprotein into the core particle
D
HDV shares the same receptor as HBV on hepatocytes and requires HBV for receptor upregulation
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A 6-month-old infant born to an HBsAg-positive, HBeAg-positive mother was not given HBIG at birth. The infant is now tested and found HBsAg-positive. What is the expected natural history if left untreated?
A
Spontaneous clearance of HBsAg within 6 months is likely, as infants mount robust immune responses
B
90% risk of progression to chronic HBV infection with high lifetime risk of cirrhosis and HCC
✓
C
Acute self-limiting hepatitis, as neonatal immune tolerance prevents chronicity
D
50% risk of chronicity, similar to adult infection risk from parenteral exposure
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Which ONE finding best distinguishes amoebic liver abscess (ALA) from pyogenic liver abscess (PLA) on laboratory evaluation?
A
Pus aspirate from ALA consistently grows E. histolytica trophozoites on culture
B
Serology (anti-amoebic IgG ELISA) is positive in >90% of ALA; pus is anchovy-sauce coloured, sterile on bacterial culture
✓
C
ALA is typically associated with high neutrophilic leucocytosis (>20,000/mm³) while PLA shows normal WBC
D
ALA pus Gram stain shows sheets of Gram-positive cocci confirming sterility
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A public health team investigates a hepatitis outbreak in a coastal town in Kerala. Serological testing of 80 patients shows: all are anti-HAV IgM negative; 60% are anti-HEV IgM positive; no HBsAg positives. Water samples from the municipal supply test positive for faecal coliform. What preventive strategy would be most impactful for the NEXT similar outbreak?
A
Mass HBV vaccination campaign targeting all adults in the town
B
Ensure safe water supply and improved sanitation; HEV vaccine for high-risk groups where available
✓
C
Immediate mass antibiotic prophylaxis with ciprofloxacin
D
Mass administration of hepatitis A immunoglobulin as post-exposure prophylaxis
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