Internal Medicine Exam Infectious Disease Management 3 — Questions and Answers
Question 1: A 55-year-old patient on prolonged broad-spectrum antibiotics develops profuse watery diarrhea. Stool toxin assay is positive for Clostridioides difficile. He has WBC 18,000 and serum creatinine 1.8 mg/dL. What is the appropriate initial treatment?
- Oral metronidazole 500 mg TID
- Oral vancomycin 125 mg QID (Correct answer)
- IV metronidazole plus oral vancomycin
- Fidaxomicin 200 mg BID
Correct answer: Oral vancomycin 125 mg QID
Fidaxomicin or oral vancomycin is preferred over metronidazole for non-severe C. difficile infection; elevated WBC and creatinine indicate non-fulminant disease still treated with oral vancomycin per current IDSA guidelines.
Question 2: An HIV-positive patient with CD4 count of 150 cells/μL is started on antiretroviral therapy. Two weeks later he develops worsening cervical lymphadenopathy and fever. Lymph node biopsy shows non-caseating granulomas. What is the most likely diagnosis?
- New opportunistic infection
- ART failure
- Immune reconstitution inflammatory syndrome (IRIS) (Correct answer)
- Drug-induced lymphadenopathy
Correct answer: Immune reconstitution inflammatory syndrome (IRIS)
IRIS occurs when recovering immunity mounts an exaggerated response to a previously subclinical infection (here, likely mycobacterial), typically 2–8 weeks after ART initiation.
Question 3: A 70-year-old nursing home resident presents with altered mental status and dysuria. Urinalysis shows pyuria and bacteriuria. She is afebrile with stable vitals. What is the BEST management?
- Start empiric antibiotics immediately
- Obtain urine culture and treat based on sensitivities
- Treat only if urine culture grows ≥10⁵ CFU/mL
- No antibiotic treatment; reassess in 48 hours (Correct answer)
Correct answer: No antibiotic treatment; reassess in 48 hours
Asymptomatic bacteriuria in elderly women should not be treated with antibiotics, as treatment does not reduce morbidity and promotes resistance; altered mental status requires workup for other causes.
Question 4: A patient with infective endocarditis due to methicillin-susceptible Staphylococcus aureus (MSSA) on a native valve is being treated. Which antibiotic provides superior outcomes?
- Vancomycin
- Nafcillin (or oxacillin) (Correct answer)
- Daptomycin
- Linezolid
Correct answer: Nafcillin (or oxacillin)
Anti-staphylococcal penicillins (nafcillin/oxacillin) are superior to vancomycin for MSSA endocarditis due to better bactericidal activity and clinical outcomes.
Question 5: A 40-year-old cave explorer develops progressive pulmonary infiltrates and mediastinal lymphadenopathy 3 weeks after visiting bat-inhabited caves in Ohio. Serum urine antigen is positive. What is the treatment?
- Fluconazole 400 mg daily
- Itraconazole 200 mg BID (Correct answer)
- Voriconazole IV for 6 weeks
- Posaconazole plus micafungin
Correct answer: Itraconazole 200 mg BID
Mild-to-moderate pulmonary histoplasmosis is treated with itraconazole for 6–12 weeks; it is the drug of choice for non-severe Histoplasma capsulatum infection.
Question 6: Which finding on echocardiogram is an absolute indication for surgical intervention in infective endocarditis regardless of hemodynamic stability?
- Vegetation >10 mm on the mitral valve
- Periannular abscess or fistula formation (Correct answer)
- Mild aortic regurgitation with preserved EF
- Mild mitral regurgitation with vegetation <5 mm
Correct answer: Periannular abscess or fistula formation
Periannular abscess or fistula indicates local invasion and structural destruction, which is an absolute surgical indication regardless of hemodynamic status.
Question 7: A 35-year-old sexually active man presents with painful genital ulcers and tender inguinal lymphadenopathy. Dark-field microscopy is negative. Which diagnosis is most likely and what is the treatment?
- Syphilis — penicillin G benzathine IM
- Herpes simplex virus — acyclovir (Correct answer)
- Chancroid (H. ducreyi) — azithromycin single dose
- Lymphogranuloma venereum — doxycycline 21 days
Correct answer: Herpes simplex virus — acyclovir
Painful vesicular/ulcerative lesions with tender lymphadenopathy in a sexually active patient are characteristic of HSV; acyclovir shortens episode duration.
Internal Medicine Exam Infectious Disease Management 3
A 55-year-old patient on prolonged broad-spectrum antibiotics develops profuse watery diarrhea.
Stool toxin assay is positive for Clostridioides difficile.
He has WBC 18,000 and serum creatinine 1.8 mg/dL.
What is the appropriate initial treatment?