Rosh Pediatrics Practice Exam

Which organism is most likely responsible for impetigo in a 2-year-old patient?

1. Staphylococcus aureus

2. Staphylococcus epidermidis

3. Streptococcus pneumoniae

4. Streptococcus pyogenes

The correct answer is: Staphylococcus aureus

Impetigo, a common bacterial skin infection in children, is primarily caused by two organisms: Staphylococcus aureus and Streptococcus pyogenes. In many cases of impetigo in young children, Staphylococcus aureus is the predominant pathogen, particularly in the more severe forms of the disease that present with extensive lesions or bullous impetigo. This organism is especially adept at colonizing skin, particularly in infants and toddlers, due to the common breaks in the skin barrier that occur from scratching, insect bites, or minor injuries. Once established, it can lead to the rapid growth of pus-filled vesicles, crusting, and significant contagion potential, highlighting why it is often the most commonly identified organism in cases of impetigo in this age group. While Streptococcus pyogenes can also cause impetigo, it is usually less prevalent compared to Staphylococcus aureus in pediatric populations. The other organisms listed, such as Staphylococcus epidermidis, are typically associated with skin flora and do not commonly cause impetigo, and Streptococcus pneumoniae is more associated with respiratory infections, not skin infections. Thus, Staphylococcus aureus emerges as the most likely causative organism for impet