A 48-year-old man comes to the emergency department due to pain in his right foot and leg. Yesterday, the patient sailed a friend's boat on the ocean and sustained a small cut to his right foot while jumping onto the dock. He stopped the bleeding using direct pressure and washed the wound with antiseptic. Last night, he awoke with throbbing pain in the right foot. The patient took ibuprofen, but the pain progressively worsened. A few hours later, he developed fever with rigors. The patient was recently diagnosed with hereditary hemochromatosis after laboratory studies showed abnormal liver aminotransferases and elevated transferrin saturation. He has not received treatment and has no other medical problems. He does not use tobacco, alcohol, or illicit drugs. Temperature is 39.4 C (103 F), blood pressure is 100/60 mm Hg, and pulse is 120/min. The patient is in moderate distress. Physical examination shows a 1.5-cm laceration on the dorsum of the right foot with extensive surrounding edema, erythema, and several dark-colored bullae. There is streaking erythema extending up the proximal right thigh. Leukocyte count is 21,000/mm3. Which of the following is the most likely causative organism of this patient's current condition?
Vibrio vulnificus | |
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*Hereditary hemochromatosis is particularly high risk because iron acts as a growth catalyst. | |
Vibrio vulnificus is a free-living, gram-negative bacterium that grows in brackish coastal water and marine environments. Levels are greatest in the summer months, reaching as high as 8% of total bacteria in some areas. Infections are primarily acquired through the consumption of raw oysters (which concentrate the bacteria) or through wound contamination during recreational activities (eg, sailing) or raw seafood handling. Most patients who become ill have liver disease (eg, alcoholic cirrhosis, viral hepatitis); those with hemochromatosis are at particularly great risk as free iron acts as an exponential growth catalyst.
Patients with wound contamination typically develop a mild cellulitis, but those with liver disease or certain comorbidities (eg, diabetes mellitus) are at risk for necrotizing fasciitis with hemorrhagic bullous lesions and septic shock. Diagnosis is made by blood and wound cultures, but treatment (intravenous antibiotics) should not be delayed due to the high risk of death. Surgical debridement may be required, particularly in high-risk patients with serious infections.
(Choice A) Pasteurella infections are typically associated with dog or cat bites/scratches and may cause rapid-onset cellulitis and necrotizing fasciitis. This patient developed a wound infection shortly after sustaining an injury while sailing, making V vulnificus more likely.
(Choice B) Pseudomonas aeruginosa skin infections commonly occur due to hot tub (not ocean) water, nail puncture wounds, and ear piercings. Folliculitis and cellulitis are more common than necrotizing fasciitis.
(Choices C and D) Staphylococcus aureus and Streptococcus pyogenes are leading causes of cellulitis and erysipelas. Although these organisms may occasionally cause necrotizing fasciitis (particularly S pyogenes), lesions typically develop over a few days (not hours). In addition, exposure to ocean water in a patient with hereditary hemochromatosis makes V vulnificus more likely.
Educational objective:
Vibrio vulnificus is a free-living marine bacterium that causes food-borne illness (through oysters) and wound infections. Wound infections may be mild, but some patients develop rapid-onset, severe, necrotizing fasciitis with hemorrhagic bullous lesions and septic shock. Patients with liver disease such as cirrhosis, viral hepatitis, and hereditary hemochromatosis are at particularly high risk.