Sure enough there was a patient in A&E with a severe blistering skin infection and they were very unwell. They were tachycardic, hypotensive and were clearly septic. Necrotising fasciitis was a definite possibility and the A&E doctors had called the orthopaedic surgeons who were on their way down to see the patient.
Alarm bells started to ring in the Microbiology Registrars head. The history was almost identical to one of the horrible questions he had recently had to answer during the Microbiology FRCPath Part 2 exam! He picked up the phone and called the Consultant Microbiologist, “this patient with necrotising fasciitis, I think they may have Vibrio vulnificus…”
Never heard of it? What is Vibrio vulnificus?
V. vulnificus is a Gram-negative bacterium that lives freely in water, especially in the brackish or salty waters of estuaries where warm river water meets the sea. The rare cases in the UK are seen in returning travellers rather than being “home-grown”.
There are two main types of infection with V. vulnificus:
- Septicaemia without an obvious source due to eating contaminated raw shellfish, which as filter feeders concentrate the bacterium
- Wound infections, including necrotising fasciitis, caused when a pre-existing skin lesion is contaminated with water containing the bacterium or when a wound is sustained when handling contaminated fish or shellfish e.g. raw oysters (vulnificus in Latin means “causing or inflicting wounds”)
Risk factors for serious infection with V. vulnificus
The main risk factors for severe infection are:
- Liver disease e.g. cirrhosis, hepatitis, alcoholism
- Haemochromatosis (a hereditary condition in which patients slowly acquire high iron levels in their bodies), the high iron levels increase the virulence of the bacterium (lots of microorganisms need iron to be virulent)
- Other chronic diseases e.g. diabetes mellitus, chronic renal failure, rheumatoid arthritis, thalassaemia and lymphoma
The septicaemia associated with V. vulnificus infection can be difficult to differentiate from septicaemia due to other causes. Careful questioning may illicit a history of potential exposure to fish, shellfish or salt water and thorough examination of the patient may identify the blistering skin lesions seen in 75% of patients with V. vulnificus septicaemia. Together, septicaemia and blistering of the skin in someone with a history of exposure should alert you to the possibility of V. vulnificus.
Shock and hypotension are common in V. vulnificus infection and these patients often develop multi-organ failure and disseminated intravascular coagulation (DIC). The mortality from V. vulnificus infection is over 40% even with treatment.
Whilst many of the V. vulnificus wound infections are limited to mild cellulitis patients with underlying diseases as risk factors may have rapidly progressive infections causing myositis and necrotising fasciitis similar to gas gangrene caused by Clostridium perfringens. This is a surgical emergency; extensive tissue debridement or amputation may be needed to save the patient’s life.
A probable diagnosis of V. vulnificus should be considered in any patient with septic shock or necrotising fasciitis who has travelled to a tropical or subtropical country and has a history of exposure to fish, shell fish or salty water.
V. vulnificus grows easily in the Microbiology laboratory on various culture media including blood agar, but this takes time and treatment should not be delayed whilst waiting for the diagnosis to be confirmed. The organism is easily identified in the laboratory using biochemical kits (e.g. API) and Maldi-TOF.
The definitive treatment of V. vulnificus septicaemia is with the synergistic combination of IV Cefotaxime or IV Ceftriaxone PLUS either PO Doxycycline or PO Minocycline. Fluoroquinolones such as Levofloxacin are also active.
The main-stay of treatment of necrotising fasciitis and severe skin and soft tissue infections is surgical. Early surgery (within 12 hours) to remove dead and diseased tissue has been shown to reduce mortality; some studies have shown that over 10% of patients require amputation of the affected limb. Only mild skin infections should be treated conservatively with either PO Doxycycline or Levofloxacin.
Given that infection with V. vulnificus is so severe and carries such a high mortality it would seem prudent to warn travellers with underlying risk factors such as liver disease, iron overload and chronic skin wounds not to expose themselves to infection. This would involve not eating raw or undercooked fish or shell fish as well as not swimming in the sea or river estuaries in the tropics. In this day of patient’s being more in charge of their medical care, is this practical advice? Retelling the outcome of this case may sharpen their appreciation of the risks they expose themselves too. There is no evidence that post-exposure prophylaxis with antibiotics is of any value.
So the Microbiology Registrar arranged for blood cultures to be taken and started the patient on Cefotaxime and Doxycycline. The orthopaedic surgeons took the patient straight to theatre and debrided the necrotic superficial tissue. The following day both the tissue and the blood cultures were growing a Gram-negative bacillus which was identified as V. vulnificus. Despite such prompt and appropriate treatment the patient had a stormy course on Critical Care and had to return to theatres a number of times, eventually having a below knee amputation. He did eventually recover and go home albeit requiring a huge amount of rehabilitation and support.
The Microbiology Registrar finally came to regard his FRCPath Part 2 exam as a great learning experience… Note: he passed the exam first time…