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Case Report |
Burns Unit, Royal Adelaide Hospital, Adelaide, South Australia 5000, Australia
Correspondence
Stephanie Chiang-Mei Low
stephanie.low{at}health.sa.gov.au
Received 8 November 2007
Accepted 11 March 2008
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The most common pet per household in Australia is the dog and many people are exposed to dog saliva daily (Australian Bureau of Statistics, 1995). Many dog-bite victims regard their injuries as minor or insignificant and do not seek medical attention. Of all dog bite victims, a small proportion develop overwhelming septicaemia (life threatening), subsequent multi-organ failure and ultimately die. The genus Capnocytophaga is part of the family Flavobacteriaceae and is in the Flavobacterium–Cytophaga rRNA homology group (Mandell et al., 2005; Vandamme et al., 1996).
These organisms are found in the oral cavity of both humans and canine species (Mandell et al., 2005). Capnocytophaga species isolated from the human oral cavity were originally described by Prevot and colleagues in 1956 (Prevot et al., 1956; Mandell et al., 2005; Bobo & Newton, 1976). In 1976 a previously undescribed Gram-negative rod was isolated from the blood and spinal fluid of a patient after a dog bite (Bobo & Newton, 1976; Hore, 2001) and was denoted as dysgonic fermenter 2 (DF-2). In 1989, Brenner and colleagues (Brenner et al., 1989) proposed the name Capnocytophaga canimorsus for this species (canimorsus being derived from the Latin for ‘dog bite’) (Hore, 2001). Further investigation also revealed a second biochemically different group that were named Capnocytophaga cynodegmi (cynodegmi being derived from the Greek for ‘dog bite’) (Hore, 2001). C. canimorsus is a Gram-negative filamentous, slow-growing, non-spore-forming facultative aerobe found in the oral cavity of canines (Hore, 2001). It is susceptible to penicillins, imipenem, erythromycin, vancomycin, clindamycin, third-generation cephalosporins, chloramphenicol, rifampicin, doxycycline and quinolones (Hore, 2001). However, it is resistant to aztreonam, trimethoprim–sulfamethoxazole and aminoglycosides (Hore, 2001). There have been a small number of case reports previously reporting human illness involving C. canimorsus.
The common presenting history is an immunocompromised patient who sustains a dog/cat bite. The incubation time for the bacterium ranges between 1 and 8 days (Hore, 2001). During this time the patient becomes increasingly unwell, with initial lethargy, tiredness, listlessness, and subsequent fevers, rigors and embolic events, including necrosis of the extremities. Multi-system organ failure follows (Hore, 2001). In these scenarios, infection is often fatal, with mortality rates in the order of 30 % (Hore, 2001; Scully et al., 1999; Pers et al., 1996).
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Case report |
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On examination she was hypotensive, peripherally shut down and febrile. She maintained her own airway but was speaking in short sentences, and the attending clinician was unable to obtain a good oxygen saturation level by pulse oximetry due to poor peripheral perfusion. Her limbs were reportedly cold, white and mottled, with her face and torso developing a purple hue. Petechial haemorrhage was suspected for the mottling and central discoloration. Consistent with the poor peripheral perfusion, her feet demonstrated decreased sensation, but retained good movement. She underwent abdominal computed tomography, which showed an enlarged gallbladder with the possibility of cholelithiasis, but no free gas or significant abdominal free fluid. She was severely oliguric.
With this picture of septic shock, she received blind broad-spectrum antibiotics after blood cultures were sent for laboratory analysis: 1 g ceftriaxone at 18.35, 500 mg metronidazole at 19.00 and 1 g meropenem at 20.20. Antibiotics did not alter the progression of sepsis or cyanotic symptoms and at 20.00 nursing staff reported progressive cyanosis with increased mottling of her ear lobes. She was moved into a resuscitation cubicle and a review by senior medical staff was requested.
At 20.30 she was reviewed by the Royal Adelaide Hospital Medi-Flight Retrieval Team who had arrived to retrieve another patient. The team were extremely concerned about her and transferred her immediately to the Royal Adelaide Hospital, arriving shortly after midnight, on the morning of the 25th June.
At the Royal Adelaide Hospital, investigations confirmed septic shock, with acidosis, leucopenia and patterns typical of disseminated intravascular coagulopathy. She was intubated. Echocardiography revealed a dilated inferior vena cava and right ventricle with subsequent right ventricular dysfunction. Inotropes were commenced (dobutamine and noradrenaline) to maintain central circulation and systolic pressure, and to support renal and cardiac function. A review of admission blood results revealed plummeting white cell counts, and coagulation and renal parameters dramatically abnormal: white cell count 2.43x109 cells l–1 (normal value 4–11x109 cells l–1), platelet count 11x109 cells l–1 (normal value 150–400x109 cells l–1), international normalized ratio 4.7 (normal value 1), activated partial thromboplastin time >200 s (normal value 25–35 s), lactate 8.0 mmol l–1 (normal value 0–2.2 mmol l–1), creatinine 160 µmol l–1 (normal value 40–90 µmol l–1).
On admission to the intensive care unit (ICU), she was diagnosed with septic shock and multi-organ failure, including adult respiratory distress syndrome, acute renal failure, disseminated intravascular coagulopathy, cardiovascular failure and leucopenia, the cause being queried as meningococcal septicaemia. Over the following 3–4 weeks, her medical state improved, with her renal, respiratory, immune, cardiovascular function and coagulopathy returning to normal.
On July 12 2007 the Royal Adelaide Hospital Burns Team were asked to review her in the ICU. Her medical condition had improved, but she had areas of black eschar on the tips of her fingers, toes, nose and various other areas (including thighs and upper arms). On examination it was clear that these darkened areas represented dry necrosis and other non-escharified tissues were discoloured and non-viable. Salvage of the majority of these tissues was impossible.
It was only at this point that an organism was cultured from the patient's blood: the causative organism was C. canimorsus. Following research into this unusual organism, further inquiry was made as to how this particular patient could have been infected. The common sites for C. canimorsus growth were discovered, and it was only then that the patient realized the significance of her small burn wound and the dog lick.
The patient was taken to theatre over the following fortnight to examine the necrotic areas, debride non-viable tissue and dress wounds using non-adhesive and antibacterial dressings. Unfortunately debridement included removal of all fingers and all toes, at the metacarpophalangeal joint/metatarsophalangeal joint level, and both thumbs at interphalangeal joint level. A below knee amputation to her left lower limb and a forefoot amputation to her right lower limb were performed. At each debridement, as much viable tissue was preserved as was possible, without putting life and vital organs in danger.
After three operative debridement procedures to eradicate all necrotic tissues, it took a further three definitive operations to close her wounds. Definitive procedures included a left below-knee amputation, amputation of all digits, with split skin grafts to cover the distal tissue defects. We also undertook reconstruction of her right forefoot. A left radial forearm free flap was harvested and anastomosed to the anterior tibial artery on the right foot, with the skin paddle overlying the medial, distal, lateral and dorsal aspects of the forefoot. The minor residual defect (3x4 cm) on the medial aspect of her right sole was filled with Integra dermal regeneration template, as was the defect created on her left forearm (from the free flap donor site). The Integra was dressed and left to integrate over the following 5 weeks, at which point the Integra sites were covered with sheet split skin graft sutured into place. The Integra filled the defect created by the harvesting of the radial forearm flap superbly and generated the best result possible.
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Discussion |
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This case is unique in that the patient was not immunocompromised at the time of contact with the dog saliva. The other significant difference is that she did not sustain a bite from her dog, but merely a lick to a superficial burn, the only possible site of entry for the bacterium.
An important ‘take away’ message from this case report is that domestic pets carry potentially lethal bacteria, and infection even in immunocompetent individuals can result in loss of life or limb. The seriousness of this particular presentation mandates a general awareness of C. canimorsus. Careful history taking might elucidate contact, enabling recognition before such serious sequelae.
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