AMC MCQ AMC MCQ - Australian Medical Council Multiple Choice Questions Infectious Diseases and Immunology Questions and Answers 3 — Questions and Answers
Question 1: A 30-year-old presents with ascending paralysis 2 weeks after a diarrheal illness caused by Campylobacter jejuni. Nerve conduction studies show demyelination. What is the diagnosis?
- Multiple sclerosis
- Guillain-Barré syndrome (Correct answer)
- Transverse myelitis
- Botulism
Correct answer: Guillain-Barré syndrome
Guillain-Barré syndrome is an autoimmune demyelinating polyneuropathy classically triggered by Campylobacter jejuni infection.
Question 2: Which test is most sensitive for the diagnosis of active tuberculosis in a sputum sample?
- Tuberculin skin test (Mantoux)
- Ziehl-Neelsen stain
- Mycobacterial culture (Correct answer)
- Interferon-gamma release assay (IGRA)
Correct answer: Mycobacterial culture
Mycobacterial culture (Lowenstein-Jensen or liquid MGIT) remains the gold standard for diagnosing active TB due to its highest sensitivity.
Question 3: A 50-year-old farmer presents with fever, headache, myalgia, and a 'rose-thorn' eschar after a tick bite in rural Queensland. Which organism is responsible?
- Borrelia burgdorferi
- Rickettsia australis (Correct answer)
- Coxiella burnetii
- Anaplasma phagocytophilum
Correct answer: Rickettsia australis
Rickettsia australis causes Queensland tick typhus, presenting with an eschar at the tick bite site, fever, and rash.
Question 4: A patient with X-linked agammaglobulinemia (Bruton's disease) would be most susceptible to which type of infection?
- Intracellular viral infections
- Fungal infections
- Encapsulated bacterial infections (Correct answer)
- Parasitic infections
Correct answer: Encapsulated bacterial infections
Bruton's agammaglobulinemia causes absence of B cells and immunoglobulins, impairing opsonization of encapsulated bacteria such as Streptococcus pneumoniae and Haemophilus influenzae.
Question 5: A 35-year-old sex worker presents with a painless indurated genital ulcer with rubbery inguinal lymph nodes. Dark-field microscopy shows spirochetes. What is the first-line treatment?
- Azithromycin 1 g orally once
- Benzathine penicillin G 2.4 million units IM once (Correct answer)
- Doxycycline 100 mg twice daily for 14 days
- Ceftriaxone 250 mg IM once
Correct answer: Benzathine penicillin G 2.4 million units IM once
Primary syphilis is treated with a single intramuscular dose of benzathine penicillin G 2.4 million units.
Question 6: Which mechanism allows Staphylococcus aureus to resist beta-lactam antibiotics in MRSA?
- Production of extended-spectrum beta-lactamase (ESBL)
- Altered penicillin-binding protein (PBP2a) encoded by mecA gene (Correct answer)
- Efflux pump overexpression
- Outer membrane impermeability
Correct answer: Altered penicillin-binding protein (PBP2a) encoded by mecA gene
MRSA resistance is mediated by the mecA gene encoding PBP2a, which has low affinity for beta-lactam antibiotics.
AMC MCQ AMC MCQ - Australian Medical Council Multiple Choice Questions Infectious Diseases and Immunology Questions and Answers 3
A 30-year-old presents with ascending paralysis 2 weeks after a diarrheal illness caused by Campylobacter jejuni.
Nerve conduction studies show demyelination.
What is the diagnosis?