A 36-year-old man comes to the emergency department with severe pain in his left leg. He is a carpenter and recalls that he had a small puncture wound from a wood splinter yesterday in his workshop. The patient washed the wound and applied a small adhesive bandage. This morning, he experienced severe pain in his left thigh and calf, and the pain has worsened since. He has no other medical problems and takes no medications regularly. His temperature is 39.4 C (103 F), blood pressure is 90/60 mm Hg, heart rate is 96/min, and respirations are 16/min. Physical examination of his left lower extremity shows slight erythema and swelling of the thigh and calf with severe tenderness to palpation. Two blisters are present on the posterior aspect of his proximal calf.
Which of the following is the most likely organism responsible for this patient's condition?

Question

A 36-year-old man comes to the emergency department with severe pain in his left leg.  He is a carpenter and recalls that he had a small puncture wound from a wood splinter yesterday in his workshop.  The patient washed the wound and applied a small adhesive bandage.  This morning, he experienced severe pain in his left thigh and calf, and the pain has worsened since.  He has no other medical problems and takes no medications regularly.  His temperature is 39.4 C (103 F), blood pressure is 90/60 mm Hg, heart rate is 96/min, and respirations are 16/min.  Physical examination of his left lower extremity shows slight erythema and swelling of the thigh and calf with severe tenderness to palpation.  Two blisters are present on the posterior aspect of his proximal calf. 
Which of the following is the most likely organism responsible for this patient's condition?

Quizplus · Accepted Answer

Explanation: 11ec2b69_bfb1_48ff_8f63_d52b617b2a46_MD0005_00 This patient has fever, hypotension, swelling, and erythema of his left leg. Notably, his leg is more painful to palpation than might be expected after visual inspection. These symptoms are very concerning for necrotizing fasciitis. Necrotizing fasciitis is a fulminant infection of the subcutaneous tissue that spreads rapidly along the fascial planes and leads to extensive tissue necrosis and shock. Two types of clinically distinct necrotizing fasciitis have been described. The most common form (type II) usually occurs in individuals with no concurrent medical illness. Many patients report a history of laceration, blunt trauma, or a surgical procedure as a predisposing factor. It is typically caused by group A Streptococcus (Streptococcus pyogenes). In contrast, type I is usually seen in patients with underlying diabetes and peripheral vascular disease. It is generally a polymicrobial infection; some commonly isolated organisms include Staphylococcus aureus, Bacteroides fragilis, Escherichia coli, group A Streptococcus, and Prevotella species. Crepitus is more common if anaerobic organisms, such as Clostridium perfringens or B fragilis, are involved. (Choice A) C perfringens is capable of causing necrotizing fasciitis, either in isolation or in combination with other bacteria. Affected areas generally have crepitus on examination due to gas production by Clostridia. C perfringens is not as commonly isolated as group A streptococci. (Choice C) Pseudomonas can cause necrotizing fasciitis in immunocompromised patients. It would not be expected to cause necrotizing fasciitis in an otherwise healthy young adult. (Choice D) S aureus can be seen as part of the polymicrobial etiology of type I necrotizing fasciitis in patients with poor peripheral circulation, such as those with diabetes. It is not usually associated with the development of necrotizing fasciitis alone. (Choice E) Staphylococcus epidermidis is associated with bloodstream infections and is the most common cause of central line-associated bloodstream infections. It is not associated with necrotizing fasciitis. Educational objective: Necrotizing fasciitis presents with pain out of proportion to other findings, swelling, and erythema. Fever and hypotension are common. Necrotizing fasciitis is often a polymicrobial infection in patients with poor peripheral circulation (ie, those with diabetes). Group A Streptococcus is the most common cause of necrotizing fasciitis in otherwise healthy patients. References: Necrotizing fasciitis: clinical presentation, microbiology, and determinants of mortality. (http://www.ncbi.nlm.nih.gov/pubmed/12925624) Necrotizing fasciitis. (http://www.ncbi.nlm.nih.gov/pubmed/20558917)

A 36-Year-Old Man Comes to the Emergency Department with Severe