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Difficulty: EasyInfectious Diseases

A 54-year-old man comes to the office due to worsening redness and swelling of his left lower leg over the past 48 hours. He reports no fever, chills, or systemic symptoms. His medical history includes hypertension and diet-controlled type 2 diabetes mellitus. Vital signs show a temperature of 37.2°C (99.0°F), blood pressure of 130/80 mm Hg, and heart rate of 78/min. Physical examination of the left lower extremity reveals a 10-cm area of poorly demarcated erythema, warmth, and tenderness over the anterior shin. There is no fluctuance, purulent drainage, or palpable fluid collection. Which of the following is the most appropriate antibiotic therapy?

  1. Oral cephalexinAnswer
  2. B
    Oral ciprofloxacin
  3. C
    Oral trimethoprim-sulfamethoxazole
  4. D
    Intravenous vancomycin
  5. E
    Topical mupirocin

Answer

Oral cephalexin
The patient presents with classic signs of mild, non-purulent cellulitis (poorly demarcated erythema, warmth, tenderness) without systemic toxicity or signs of an abscess (no fluctuance or purulence). The most common pathogens responsible for non-purulent cellulitis are beta-hemolytic streptococci (e.g., Streptococcus pyogenes) and methicillin-susceptible Staphylococcus aureus (MSSA). Oral cephalexin (a first-generation cephalosporin) provides excellent targeted coverage for these organisms and is a standard first-line treatment for uncomplicated cases.

Step-by-Step Solution

1
Identify the clinical syndrome based on the physical examination.
The patient has localized erythema, warmth, and tenderness without fluctuance or purulence, indicating mild non-purulent cellulitis.
Differentiating purulent from non-purulent skin infections dictates the likely pathogens and the appropriate antibiotic coverage.
2
Determine the most likely causative organisms.
Beta-hemolytic streptococci (e.g., Streptococcus pyogenes) and methicillin-susceptible Staphylococcus aureus (MSSA) are the primary pathogens.
Non-purulent cellulitis is overwhelmingly caused by beta-hemolytic streptococci, whereas purulent infections are more commonly associated with Staphylococcus aureus (including MRSA).
3
Select the appropriate targeted antimicrobial therapy.
Oral cephalexin provides excellent coverage for both beta-hemolytic streptococci and MSSA.
For mild infections without systemic signs (such as high fever or tachycardia), narrow-spectrum oral therapy is preferred, following principles of antibiotic stewardship.

Key Concept

Mild, non-purulent cellulitis is primarily caused by beta-hemolytic streptococci and should be treated with targeted, narrow-spectrum oral antibiotics such as cephalexin, dicloxacillin, or penicillin.
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Infectious Diseases

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