Internal Medicine Exam Common Infectious Diseases 5 — Questions and Answers
Question 1: A 40-year-old patient develops fever, headache, and a petechial rash spreading from wrists and ankles centrally after a camping trip in North Carolina. What is the most likely diagnosis?
- Meningococcemia
- Rocky Mountain spotted fever (Correct answer)
- Lyme disease
- Ehrlichiosis
Correct answer: Rocky Mountain spotted fever
Rocky Mountain spotted fever (Rickettsia rickettsii) classically begins with fever and headache before a centripetal petechial rash appears on wrists and ankles; immediate doxycycline is life-saving.
Question 2: Which antibiotic is first-line for treatment of Lyme disease presenting with erythema migrans in an adult?
- Amoxicillin IV for 28 days
- Doxycycline 100mg orally twice daily for 10–21 days (Correct answer)
- Ceftriaxone 2g IV for 14 days
- Azithromycin 500mg once daily for 7 days
Correct answer: Doxycycline 100mg orally twice daily for 10–21 days
Doxycycline orally for 10–21 days is first-line for early Lyme disease (erythema migrans) in adults; IV ceftriaxone is reserved for neurologic or cardiac involvement.
Question 3: A patient with recurrent furunculosis caused by MRSA is cleared but continues to have household transmission. Which decolonization strategy is most appropriate?
- Oral clindamycin prophylaxis indefinitely
- Intranasal mupirocin ointment plus chlorhexidine body wash (Correct answer)
- Systemic vancomycin for all household contacts
- No treatment needed after the index case resolves
Correct answer: Intranasal mupirocin ointment plus chlorhexidine body wash
Intranasal mupirocin and chlorhexidine bathing decolonize MRSA carriage in both the index patient and household contacts, reducing recurrence.
Question 4: A 65-year-old immunocompromised patient develops fever and a new pulmonary infiltrate with a halo sign on CT chest. What is the most likely diagnosis?
- Pneumocystis jirovecii pneumonia
- Invasive pulmonary aspergillosis (Correct answer)
- Cytomegalovirus pneumonitis
- Bacterial lung abscess
Correct answer: Invasive pulmonary aspergillosis
The halo sign (ground-glass opacity surrounding a nodule) on CT chest in an immunocompromised host is classic for invasive pulmonary aspergillosis.
Question 5: A 50-year-old patient with cirrhosis presents with fever, abdominal pain, and ascites with PMN count > 250 cells/μL on paracentesis. What is the empiric treatment of choice?
- Metronidazole plus ciprofloxacin
- IV cefotaxime (or ceftriaxone) (Correct answer)
- Oral amoxicillin-clavulanate
- Piperacillin-tazobactam plus vancomycin
Correct answer: IV cefotaxime (or ceftriaxone)
IV third-generation cephalosporins (cefotaxime or ceftriaxone) are the standard empiric therapy for spontaneous bacterial peritonitis.
Question 6: Which HIV-associated opportunistic infection is prevented by trimethoprim-sulfamethoxazole prophylaxis when the CD4 count falls below 200 cells/μL?
- Toxoplasma gondii encephalitis only
- Pneumocystis jirovecii pneumonia (PCP) and Toxoplasma (Correct answer)
- Mycobacterium avium complex
- Cytomegalovirus retinitis
Correct answer: Pneumocystis jirovecii pneumonia (PCP) and Toxoplasma
TMP-SMX prophylaxis at CD4 < 200 cells/μL prevents both PCP and Toxoplasma encephalitis (the latter when CD4 < 100 and Toxoplasma IgG positive).
Question 7: A traveler returns from Southeast Asia with watery diarrhea, nausea, and abdominal cramps starting 6 hours after eating rice. No fever is present. Which pathogen is most consistent with this presentation?
- Vibrio cholerae
- Salmonella typhi
- Bacillus cereus (emetic toxin) (Correct answer)
- Campylobacter jejuni
Correct answer: Bacillus cereus (emetic toxin)
Bacillus cereus emetic syndrome presents within 1–6 hours of ingesting preformed toxin in starchy foods like rice, causing vomiting and cramps without fever.
Internal Medicine Exam Common Infectious Diseases 5
A 40-year-old patient develops fever, headache, and a petechial rash spreading from wrists and ankles centrally after a camping trip in North Carolina.
What is the most likely diagnosis?