A 65-year-old woman comes to the emergency department due to 1 day of painful swelling of the left side of her face, associated with high fever and chills. She has had no facial trauma or injury to that area. The patient was diagnosed with type 2 diabetes mellitus 3 years ago and achieves good glycemic control with diet, exercise, and oral hypoglycemic agents; she has no known complications. Temperature is 39.2 C (102.6 F), blood pressure is 125/75 mm Hg, and pulse is 90/min. Physical examination shows a warm, tender, erythematous rash with raised, well-demarcated borders on the left side of the face, including the left external ear. The ear canal has no discharge, and hearing is intact. Mild regional lymphadenopathy is present. Which of the following is the most likely causative organism of this patient's infection?
Common skin infections | ||
Infection | Organism | Manifestations |
Erysipelas |
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Cellulitis (nonpurulent) |
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Cellulitis (purulent) |
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MRSA = methicillin-resistant Staphylococcus aureus;MSSA = methicillin-sensitive S aureus. | ||
Erysipelas is a skin infection of the upper dermis and superficial lymphatic system most commonly caused by group A Streptococcus. Infections take hold in areas of skin disruption, often due to minor trauma, inflammation, concurrent infection, or edema. Patients rapidly develop systemic symptoms (fever, chills), regional lymphadenitis, and a warm, tender, erythematous rash notable for raised, sharply demarcated borders. Involvement of the external ear is particularly suggestive of erysipelas as this skin lacks a lower dermis level (making cellulitis, a deeper skin infection, unlikely).
The diagnosis of erysipelas is usually based on clinical findings, but blood cultures are useful in patients with extensive rash, systemic toxicity, or underlying comorbidities (eg, diabetes). Most patients receive intravenous antibiotics (eg, ceftriaxone, cefazolin), but those without systemic symptoms may be treated with oral medication (eg, amoxicillin). If possible, the underlying source of skin breach should be addressed to help prevent recurrence.
(Choice A) Clostridium perfringens causes gas gangrene and manifests with severe pain, bullae, soft tissue crepitus, and signs of systemic toxicity (including shock and multiorgan failure). This patient does not have bullous lesions or crepitus.
(Choices B, D, E, and F) Enterococcus, Haemophilus influenzae, Pseudomonas aeruginosa, and Staphylococcus aureus usually cause cellulitis, a deeper skin infection of the lower dermis and subcutaneous fat. Cellulitis tends to have a slower onset (over days), indistinct/flat borders, and fewer initial systemic symptoms (eg, fever). S aureus in particular is associated with purulent skin and soft tissue infections (eg, pus drainage, furuncle/carbuncle/abscess formation). Pseudomonas can also cause external otitis, which is often accompanied by ear pain and discharge, an edematous ear canal, and hearing loss (not seen in this patient).
(Choice G) Streptococcus agalactiae (group B Streptococcus) primarily causes peripartum infections but may rarely cause erysipelas in an adult. Group A Streptococcus is far more common.
(Choice H) Streptococcus pneumoniae usually causes respiratory tract infections (eg, pneumonia), meningitis, or bacteremia.
Educational objective:
Erysipelas is a superficial skin infection that manifests with the acute onset of systemic symptoms (fever, chills), regional lymphadenitis, and a warm, tender, erythematous rash with raised, sharply demarcated borders. The majority of erysipelas cases are caused by group A Streptococcus.