Internal Medicine Exam Common Infectious Diseases 3 — Questions and Answers
Question 1: A healthcare worker sustains a needlestick from an HIV-positive patient. Post-exposure prophylaxis should ideally be started within what timeframe?
- 72 hours (Correct answer)
- 24 hours
- 1 week
- 48 hours
Correct answer: 72 hours
HIV post-exposure prophylaxis (PEP) should be initiated as soon as possible but within 72 hours of exposure to be effective.
Question 2: Which clinical feature differentiates cellulitis from necrotizing fasciitis and should prompt urgent surgical evaluation?
- Erythema and warmth
- Pain out of proportion to appearance with skin crepitus (Correct answer)
- Leukocytosis above 12,000
- Fever greater than 38.5°C
Correct answer: Pain out of proportion to appearance with skin crepitus
Pain disproportionate to clinical appearance and crepitus (subcutaneous gas) are hallmark findings of necrotizing fasciitis requiring emergent surgical debridement.
Question 3: A 45-year-old man presents with fever, right upper quadrant pain, and jaundice after a trip to Egypt. Ultrasound shows a cystic liver lesion. Serology is positive for Entamoeba histolytica. What is the treatment?
- Metronidazole followed by paromomycin (Correct answer)
- Albendazole alone
- Mebendazole for 3 months
- Praziquantel single dose
Correct answer: Metronidazole followed by paromomycin
Amebic liver abscess is treated with metronidazole to eradicate invasive disease, followed by a luminal agent like paromomycin to eliminate intestinal cysts.
Question 4: Which laboratory finding is most consistent with Clostridium difficile colitis?
- Stool culture positive for gram-positive rods
- Positive stool toxin assay (GDH + toxin EIA) (Correct answer)
- Blood culture growing C. difficile
- Elevated stool lactoferrin only
Correct answer: Positive stool toxin assay (GDH + toxin EIA)
Diagnosis of C. difficile infection requires detection of toxin; the two-step algorithm using GDH screening followed by toxin EIA or NAAT is standard.
Question 5: A 22-year-old college student presents with fever, pharyngitis, and splenomegaly. Monospot test is positive. Which complication warrants restriction from contact sports?
- Hepatitis
- Splenic rupture (Correct answer)
- Airway obstruction
- Hemolytic anemia
Correct answer: Splenic rupture
Splenic rupture is the most feared complication of infectious mononucleosis, and patients should avoid contact sports for at least 3–4 weeks.
Question 6: A patient presents with fever, cough, and bilateral hilar adenopathy on chest X-ray after exposure to bird droppings in the Ohio River Valley. What is the most likely diagnosis?
- Coccidioidomycosis
- Blastomycosis
- Histoplasmosis (Correct answer)
- Aspergillosis
Correct answer: Histoplasmosis
Histoplasma capsulatum is endemic to the Ohio and Mississippi River Valleys and is associated with exposure to bat and bird droppings.
Question 7: Which antibiotic class is contraindicated in a pregnant woman diagnosed with a chlamydial infection?
- Macrolides
- Tetracyclines (Correct answer)
- Beta-lactams
- Sulfonamides in first trimester
Correct answer: Tetracyclines
Tetracyclines (including doxycycline) are contraindicated in pregnancy due to effects on fetal bone and tooth development; azithromycin is the preferred alternative.
Internal Medicine Exam Common Infectious Diseases 3
A healthcare worker sustains a needlestick from an HIV-positive patient.
Post-exposure prophylaxis should ideally be started within what timeframe?