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Self-Assessment Questions

Infectious Diseases

Community-Acquired Methicillin-Resistant
Staphylococcus aureus Infection: Review Questions

Jeannina A. Smith, MD

Dr. Smith is a clinical instructor, Department of Infectious Diseases, University of Michigan, Ann Arbor, MI.



Choose the single best answer for each question.

Questions 1 to 4 refer to the following case.
A previously healthy 25-year-old man presents to the clinic with a 3-day history of painful swelling in his left thigh that has been increasing in size. He has been seen in the emergency department 2 times in the past 3 months for similar lesions, which he describes as “spider bites” on his buttocks and abdomen. On physical examination, the patient is afebrile and has normal blood pressure. He has a 3-cm fluctuant mass on his left lateral thigh surrounded by a 4-cm ring of erythema (Figure). The mass is warm and tender.


1. What is the most important next step in this patient’s management?
  1. Apply topical diphenhydramine and discharge home
  2. Initiate intravenous (IV) vancomycin
  3. Obtain cultures and prescribe oral cefalexin
  4. Perform incision and drainage, obtain cultures, and prescribe oral amoxicillin clavulanate
  5. Perform incision and drainage, obtain cultures, and prescribe oral clindamycin
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2. The patient presents 1 week later for follow-up. Laboratory cultures obtained from purulent material expressed from the mass demonstrate many gram-positive cocci on Gram stain and Staphylococcus aureus growth with the following susceptibility pattern: penicillin R, oxacillin R, cefazolin R, tetracycline S, trimethoprim/sulfamethoxazole S (TMP/SMX), clindamycin S, and erythromycin R. The patient most likely has acquired this strain of bacteria from which of the following?

  1. An arthropod vector
  2. Close physical contact with other athletes at a health club
  3. Contaminated food
  4. His grandmother who lives in a nursing home
  5. Handling reptiles
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  3. What additional laboratory testing should be performed to confirm that the antibiotic administered has activity against the methicillin-resistant S. aureus (MRSA) strain identified in this patient?
  1. D-test
  2. E-test
  3. Schlichter test
  4. Testing for the mec-A gene
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4. The patient is concerned by his recurrent infections and asks if S. aureus can live in healthy people. Which of the following is the most appropriate response to this patient’s concern?

  1. Healthy people do not harbor S. aureus
  2. S. aureus is only acquired through contact with inanimate surfaces
  3. S. aureus colonization is common and affects as many as 20% to 40% of the US population
  4. Only patients with breaks in the skin or chronic disease manifest illness/infection
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5. A previously healthy 16-year-old girl presents to the emergency department with respiratory distress after developing a high fever, dry cough, coryza, and myalgias 2 weeks ago. Her parents add that her symptoms had previously improved, but the patient developed high fever, productive cough, and shortness of breath 1 day prior to presentation. Several family members recently had similar symptoms and were diagnosed with influenza. On physical examination, the patient is febrile (102°F). An initial chest radiograph reveals diffuse bilateral interstitial infiltrates. Due to tachypnea, the patient is emergently intubated. A sputum sample reveals more than 25 white blood cells and less than 10 squamous epithelial cells. There are a large number of gram-positive cocci in clusters, but no other organisms are seen on Gram stain. Initial antibiotic therapy should include which of the following?

  1. Daptomycin
  2. Gentamicin
  3. Levofloxacin
  4. Linezolid
  5. Ribavirin
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