Question 125

Question:

A 66 year-old man presents complaining of fever and thigh pain. 24 hours ago he noted intense pain followed by redness and swelling in a small area of the right lateral thigh. Since then, the affected area has progressively increased to the current state, which on exam includes almost all of the right thigh and buttock, the lateral aspect of the right leg, and extends to the abdomen and right flank, 5 cm above the iliac crest. Crepitus is present on palpation. Leukocyte count is 14,000/mm3. Blood cultures are pending. Which organism is the most common etiologic agent of this clinical scenario?

Correct Answer: A.  Group A Streptococcus

This patient has necrotizing fasciitis. It is a rapidly progressive bacterial infection that spreads along fascial planes. It may follow trauma, but this will not always be present in the history. Crepitus is often appreciated, indicating subcutaneous air. Treatment includes starting IV antibiotics immediately, early and aggressive surgical debridement, and tetanus prophylaxis. It is classically caused by group A Streptococcus, but other etiologic organisms include Clostridium perfringens and Bacteroides fragilis (it is also often polymicrobial). Although Staphylococci are skin flora, they are not typically implicated in necrotizing fasciitis. Mycoplasma pneumoniae and Moraxella catarrhalis are causes of community-acquired pneumonia and do not cause necrotizing fasciitis.