Case 3

A previously 33-year-old male presents to the emergency room in Buemont, TX with a 3-day history of fevers, pain and swelling of his left calf. He has been volunteering during the relief efforts, and while assisting in a rescue operation during the recent floods he sustained a laceration to his left calf.

Physical examination of the left lower extremity revealed a 10 cm laceration overlying the lateral aspect of left calf. The calf is edematous, erythematous and diffusely tender. Crepitation is palpated. The left inguinal and popliteal lymph nodes are enlarged and painful.

An X-ray done to rule out a fracture revealed subcutaneous air in the calf.

Which of the following is the most likely causative organism in this case:

1. Vibiro vulnificus
2. Aeromonus hydrophila
3. Erhusiopathiae rhusiopathiae
4. Mycobaterium marinum

Answer: Aeromonus hydrophila

The above case was a case of necrotizing fasciitis caused by Aeromonus hydrophilia. Aeromonas is a gram negative bacillus widely distributed in warmer freshwater, estuarine, and marine environments. This organism resides in the gut of the leech Hirudo medicinalis, where they assist in the enzymatic digestion of the blood ingested by the leech. Aeromonas causes skin and soft tissue infection typically after tissue injury followed by exposure to contaminated water or soil. Infections can be fulminant and severe, leading to necrotizing fasciitis, myonecrosis and sepsis. It has also been implicated in diarrheal diseases, which can be acute or chronic in nature. \

Vibiro vulnificus is similarly associated with wound infections after water exposure, however it is classically associated with salt or brackish water exposure or through the handling of seafood (in particular oysters). Mycobaterium marinum has a slower, more indolent course and is usually not associated with systemic signs of toxicity, as was the case with the above patient. E. rhusiopathiae most commonly causes a localized cutaneous eruption on the fingers or hands of fishermen or seafood packers who suffer minor trauma while handling contaminated shrimp, crab, or fish. It is not associated with necrotizing fasciitis.

Diagnosis of Aeromonas infections such as the one above is through wound, tissue or blood cultures. Aeromonus spp. are frequent B-lactamase producers, hence empiric agents for treatment include fluoroquinolones or third generation cephalosporins. Patients undergoing leech therapy often receive chemoprophylaxis with ciprofloxacin for 3-5 days during leech applications.

The cases this week were submitted by Ahmed Babiker, 1st Year ID Fellow at Pitt.