Infectious Disease Management Flashcards

A 45-year-old man with HIV (CD4 50 cells/µL) presents with fever, headache, and neck stiffness. CSF shows elevated protein, low glucose, and India ink positive organisms. What is the first-line treatment?

Answer: Liposomal amphotericin B plus flucytosine

Cryptococcal meningitis in HIV patients is treated with induction therapy using liposomal amphotericin B plus flucytosine for 2 weeks, followed by fluconazole consolidation.

A 30-year-old woman presents with dysuria and urinary frequency. Urine culture grows >100,000 CFU/mL of E. coli sensitive to all agents. She is 10 weeks pregnant. What is the appropriate antibiotic?

Answer: Nitrofurantoin 100mg BID x 5 days

Nitrofurantoin is safe in the second trimester and is first-line for uncomplicated UTI in pregnancy; TMP-SMX and fluoroquinolones are avoided due to fetal risks.

A 60-year-old man with COPD is hospitalized with healthcare-associated pneumonia. He has no prior antibiotic exposure. What empiric coverage is most appropriate?

Answer: Piperacillin-tazobactam plus vancomycin

Healthcare-associated pneumonia requires broad-spectrum coverage for MRSA and Pseudomonas, making piperacillin-tazobactam plus vancomycin the appropriate empiric regimen.

A 55-year-old patient develops fever and diarrhea 4 days after starting clindamycin for a skin infection. Stool testing is positive for C. difficile toxin. She has her first episode. What is the preferred treatment?

Answer: Fidaxomicin 200mg BID x 10 days

Current IDSA guidelines recommend fidaxomicin as preferred first-line therapy for initial C. difficile infection due to lower recurrence rates compared to vancomycin.

A 25-year-old man presents with a painless penile ulcer with indurated borders and bilateral inguinal lymphadenopathy. Dark-field microscopy confirms the diagnosis. What is the treatment of choice?

Answer: Benzathine penicillin G 2.4 million units IM single dose

Primary syphilis is treated with benzathine penicillin G 2.4 million units IM as a single dose, which is curative for early syphilis.

A 40-year-old woman from Southeast Asia presents with fever, night sweats, weight loss, and a productive cough for 3 months. AFB smear is positive. She starts RIPE therapy. After 2 months, cultures show full susceptibility. What is the total treatment duration?

Answer: 6 months total

Drug-susceptible pulmonary tuberculosis is treated with 2 months of RIPE followed by 4 months of rifampin and isoniazid, for a total of 6 months.

A 35-year-old man with a dog bite to his hand 8 hours ago presents for evaluation. He is up to date on tetanus and the wound has been thoroughly irrigated. What organism most commonly causes infection in dog bites?

Answer: Pasteurella multocida

Pasteurella multocida is the most common pathogen isolated from dog and cat bite wounds, typically causing rapid-onset cellulitis within 24 hours.

A 70-year-old man undergoes hip arthroplasty and develops fever and wound drainage at day 14. Joint aspiration grows MRSA. What is the antibiotic of choice for MRSA prosthetic joint infection?

Answer: Vancomycin IV dosed to trough 15-20 mcg/mL

Vancomycin IV remains the standard of care for MRSA prosthetic joint infections, typically combined with rifampin for biofilm penetration in device-associated infections.

A 50-year-old immunocompromised patient presents with fever, pleuritic chest pain, and a pulmonary nodule with halo sign on CT. Galactomannan antigen returns elevated. What is the most appropriate initial antifungal?

Answer: Voriconazole 6mg/kg IV q12h x 2 doses, then 4mg/kg q12h

Voriconazole is the preferred first-line treatment for invasive pulmonary aspergillosis based on superior efficacy demonstrated in landmark clinical trials.

A 28-year-old woman presents with fever, rash on palms and soles, and headache after camping in North Carolina in May. Peripheral smear shows no parasites but thrombocytopenia and hyponatremia are present. What is the treatment?

Answer: Doxycycline 100mg BID

Rocky Mountain Spotted Fever (Rickettsia rickettsii) is treated empirically with doxycycline 100mg BID, which should not be delayed awaiting confirmatory testing.

A 65-year-old man with a mechanical aortic valve develops fever, positive blood cultures for viridans streptococcus, and a new perivalvular abscess on TEE. What does the abscess finding indicate?

Answer: Cardiac surgery consultation is required

Perivalvular abscess is a class I indication for urgent cardiac surgery in prosthetic valve endocarditis, as medical therapy alone is insufficient.

A 45-year-old HIV-positive man (CD4 180, not on ART) is diagnosed with PCP pneumonia. His PaO2 on room air is 58 mmHg. In addition to TMP-SMX, what adjunctive therapy should be started?

Answer: Systemic corticosteroids (prednisone 40mg BID)

Adjunctive corticosteroids are indicated for PCP when PaO2 35 mmHg, as they reduce mortality by preventing inflammatory deterioration.

A 22-year-old college student presents with fever, pharyngitis, cervical lymphadenopathy, and splenomegaly. Heterophile antibody test is positive. Which complication requires activity restriction?

Answer: Splenic rupture risk

Splenic rupture is a rare but life-threatening complication of infectious mononucleosis; patients should avoid contact sports and strenuous activity for at least 3-4 weeks.

A 55-year-old diabetic woman presents with right facial pain, black eschar on the palate, and periorbital edema. CT shows sinus involvement extending to the orbit. What is the likely pathogen?

Answer: Mucor/Rhizopus species

Rhinocerebral mucormycosis caused by Mucorales (Mucor/Rhizopus) classically occurs in diabetic ketoacidosis, presenting with black necrotic eschar and rapid orbital/CNS spread.

A 40-year-old man returns from a trip to sub-Saharan Africa with fever, chills, and headache starting 10 days after return. Peripheral blood smear shows ring forms in >5% of RBCs with multiple rings per cell. What is the treatment?

Answer: IV artesunate

Severe falciparum malaria (parasitemia >5%) requires IV artesunate, which is now available in the US and superior to IV quinine for severe disease.

A 68-year-old man on hemodialysis develops bacteremia with MSSA. TEE shows no vegetation. What is the recommended duration of antibiotic therapy for uncomplicated MSSA bacteremia?

Answer: 14 days

Uncomplicated S. aureus bacteremia (no endocarditis, no metastatic focus, clinical improvement by 72h) requires 14 days of IV anti-staphylococcal therapy.

A 35-year-old woman is found to have latent tuberculosis infection (LTBI) with a positive IGRA. She has no active TB symptoms. She is not pregnant and has no liver disease. What is the preferred LTBI treatment regimen?

Answer: Isoniazid plus rifapentine weekly for 12 weeks (3HP)

The 3HP regimen (weekly isoniazid plus rifapentine for 12 weeks) is preferred for LTBI due to superior completion rates compared to 9-month isoniazid monotherapy.

A 45-year-old male traveler develops profuse watery diarrhea, nausea, and vomiting 2 days after returning from India. Stool cultures show Vibrio cholerae. What is the primary treatment priority?

Answer: IV fluid resuscitation with Ringer's lactate

Aggressive fluid and electrolyte replacement is the cornerstone of cholera treatment, as severe dehydration causes most deaths; antibiotics are adjunctive.

A 30-year-old woman with recurrent UTIs asks about post-coital prophylaxis. She has 3 UTIs per year, all temporally related to sexual intercourse. Which regimen is appropriate?

Answer: Single-dose TMP-SMX SS taken within 2 hours of intercourse

Post-coital single-dose TMP-SMX or nitrofurantoin is effective prophylaxis for women whose UTIs are clearly linked to sexual activity.

A 55-year-old man with diabetes presents with right lower extremity cellulitis and fever. He was treated with cephalexin for 5 days without improvement. What additional coverage should be empirically added?

Answer: TMP-SMX or doxycycline (MRSA coverage)

Failure to improve on beta-lactam therapy for cellulitis should prompt consideration of MRSA, and empiric MRSA coverage with TMP-SMX or doxycycline should be added.