A young previously well man presented with fever, left lower limb pain, erythema and swelling for 3 days. A week ago, he had stepped on a sea urchin while at a regional beach resort, which had resulted in several penetrating injuries to his left foot. He had self-administered first aid at that point, removing several black spine fragments and washing the wounds with water.

Sea urchin – photo taken at a regional beach.

Clinical examination revealed a mildly toxic-looking young man with a temperature of 39.3 degrees Celsius but who was hemodynamically stable. There was tender cellulitis up to mid-shin, with a little yellowish pus present at a couple of puncture sites on the foot. No spine fragments were visible.

Questions

1. What are the possible micro-organisms causing the lower limb infection?
2. How should this patient be managed?

[Updated 30th June 2018]

The majority of sea urchin stings results in penetrating injuries that are rarely extremely painful (relative to stings by other sea creatures). The main consideration is retained fragments of the stings, which may result in persistent pain, infection, and subsequent foreign granuloma formation. There are a small number of case reports describing infection post-sea urchin sting. These typically report a mix of saltwater bacteria (especially Vibrio spp. and rarely Mycobacterium marinum) and skin flora.

In this particular case, if resources permit, the foot should still be carefully examined for spine fragments and an MRI performed if available, with surgical exploration if there is a suggestion of deep-seated spine fragments. Culture-guided antibiotic therapy is best, although most physicians will prescribe antibiotics that typically cover marine and skin pathogenic flora, which include doxycycline and amoxicillin/clavulanate among others.