Abstract
This is a presentation of a case of mono microbial necrotising fasciitis due to the unusual organism Salmonella enteritidis. The patient presented with swelling and blistering of the right calf. There are only five other such cases reported in the literature. This was the only case that had positive blood cultures for the organism. Prompt and appropriate treatment was intuited but the patient died because of multi-organ failure.
BACKGROUND
Necrotising fasciitis is an uncommon, rapidly progressive and life-threatening soft tissue infection characterised by rapidly spreading inflammation and necrosis involving the skin, subcutaneous fat and fascia. Usually, it is a synergistic polymicrobial infection involving both aerobic and anaerobic bacteria, but single pathogen infections involving Streptococcus pyogenes and Staphylococcus aureus alone or in combination are not uncommon.1,2
We describe a case of fatal lower limb necrotising fasciitis associated with septic shock in a 55-year-old woman. The causative organism was identified as Salmonella enterica serotype Enteritidis (S enteritidis), which is a highly unusual agent of necrotising fasciitis.
CASE PRESENTATION
A 55 year-old woman presented with progressive pain on her right leg for the past 4 days associated with fever, chills and rigors. One day before admission, the pain become excruciating and was accompanied by reddish discolouration of the overlying skin and formation of blisters. No history of precipitating injury or watery diarrhoea was elicited. Current medical problems included non-insulin dependent diabetes mellitus for which she was taking oral hypoglycaemics and she was compliant to the treatment.
The initial physical examination revealed an ill-looking woman with the following vital signs: temperature 38°C; pulse 90 beats per min; blood pressure 110/70 mm Hg and respiration rate 28 breaths per min. Her right lower limb was swollen, warm, tender and tense on palpation with an area of purple-red discolouration over the affected side. There was a fluctuant swelling over the calf measuring 4×5 cm with an overlying ruptured blister discharging serous fluid. Circulation in the limbs was good and there was no neurological deficit.
INVESTIGATIONS
Initial blood investigations revealed marked leucocytosis (25.4×103/μl) with a left shift, normochromic normocytic anaemia (haemoglobin 10.3 g/dl) and platelets were 373×103/μl. Blood gas revealed metabolic acidosis and her coagulation profile was also slightly deranged with prolonged prothrombin time and partial thromboplastin time and blood glucose was 18 mmol/l. Her urine ketones were negative. The radiography of the right tibia/fibula and ankle did not show any evidence of osteomyelitis or gas gangrene (gas in the soft tissue).
DIFFERENTIAL DIAGNOSIS
Necrotising fasciitis, gas gangrene and right calf abscess.
TREATMENT
On admission, she was started empirically on intravenous ceftriaxone 1 g daily and metronidazole 500 mg three times daily, intravenous insulin and she was hydrated adequately. Within 10 hours after admission, once she was haemodynamically stable, she underwent an emergency wound debridement. Intra-operatively, it was noted that the degree of tissue necrosis was extensive involving the soft tissue and fascia. An extensive debridement was carried out and tissue samples were submitted to the microbiology laboratory. Gram stain performed on the infected tissue showed numerous Gram-negative rods.
OUTCOME AND FOLLOW-UP
Post-operatively, the patient was ventilated and managed in the intensive care unit. Over the next few hours, she progressed rapidly into septic shock with acute renal failure, hypotension and coagulopathy, and she was maintained on ventilatory support, inotropes and haemodialysis.
However, her condition continued to deteriorate and she was planned for further debridement. Intra-operatively, it was noted that the infection had extended above the knee and a right above knee amputation was performed in an attempt to control the source of sepsis. Meanwhile, blood cultures taken on admission demonstrated Gram-negative rods and antibiotics were changed to intravenous imipenem (500 mg every 6 hours) for a broader microbial coverage. Unfortunately, despite adequate intensive care, her condition continued to deteriorate and the patient died because of multiple organ failure secondary to septic shock 4 days after admission.
The Gram-negative rods isolated from blood cultures and tissue was identified as S enteritidis. The isolate was sensitive to ampicillin, co-trimoxazole, chloramphenicol, ceftriaxone and ciprofloxacin. Anaerobic cultures and rectal swab culture did not yield any pathogen.
DISCUSSION
Necrotising fasciitis is a rare and severe soft tissue infection characterised by rapidly progressing necrosis of the subcutaneous tissue and fascia. Necrotising fasciitis is often polymicrobial (type-1 necrotising fasciitis). In these patients, aerobes like streptococcal species, staphylococcal species, enterococci, enterobacteriaceae and anaerobes like Bacteroides and Clostridium species are commonly isolated.1,2 Monomicrobial (type-II necrotising fasciitis) infection is reported in about 15–28% of cases1,3 and usually involves beta-haemolytic Streptococcus Lancefield group A (S pyogenes) alone or in combination with S aureus.2 Necrotising fasciitis caused by S enteritidis is a very rare entity and we believe that this is the first reported case associated with bacteraemia and fatality. A summary of reported necrotising fasciitis caused by S enteritidis is shown in Table 1.
Table 1.
Summary of clinical characteristics of patients reported with Salmonella enteritidis necrotising fasciitis
| Ref | Age/sex | Underlying disease | NF site | Diarrhoea | Culture source | Serogroup | Serotype | Outcome |
| 4 | 76/M | Temporal arteritis on steroids | Right lower limb | Yes | Subcutaneous aspirate | D | S enteritidis Mono-microbial | Survived |
| 5 | 2/M | Caecal perforation | Abdominal wall | Yes | Pus | D | S enteritidis Poly-microbial | Survived |
| 6 | 67/F | Diabetes mellitus | Right neck | No | Wound | D | S enteritidis Mono-microbial | Survived |
| 6 | 39/M | Diabetes mellitus | Left neck | No | Wound | D | S enteritidis Mono-microbial | Survived |
| 7 | 57/F | Multiple myeloma | Right lower limb | Yes | Tissue and urine | D | S enteritidis Mono-microbial | Survived |
| PR | 55/F | Diabetes mellitus | Right lower limb | No | Tissue and blood | D | S enteritidis Mono-microbial | Died |
NF, necrotising fasciitis; PR, present report.
Of the six cases, five harboured monomicrobial infection; three involving the lower limb and two involving the neck. Only one case, which involved necrotising fasciitis of the abdominal wall, was polymicrobial in nature as it was associated with caecal perforation. Unlike this case, which was associated with bacteraemia, in all the other cases the isolates were recovered from pus or tissue only. Diabetes mellitus, peripheral vascular disease, alcoholism with chronic liver disease and cancer with immunosuppression3 are some of the predisposing conditions to necrotising fasciitis. The portal of entry of infection may be identified in 50% of cases and includes the sites of pre-existing ulcers and bed sores, burns, trauma, postoperative infection, injection sites and intravenous lines;3 this is not evident in our case. Gastroenteritis, which was present in three out of six reported cases, was not a feature in our patient. Not all cases of non-typhoidal salmonella are associated with diarrhoea and the presence of bacteraemia without gastroenteritis may be a marker of underlying immunosuppression.8 Use of H2 antagonists, proton pump inhibitors, consumption of raw eggs and products containing raw eggs have been associated with endemic S enteritidis infection.9
Non-typhoidal salmonella species are important food borne pathogens that can result in acute gastroenteritis. However, invasion beyond the gastrointestinal tract occurs in approximately 5% of patients10 and presents with a wide variety of manifestations that include bacteraemia, mycotic aneurysms, meningitis, osteomyelitis, septic arthritis and pneumonia.10,11 Necrotising fasciitis is a highly unusual presentation of non-typhoidal salmonella infection. Non-typhoidal salmonella tends to affect patients with a wide variety of immunocompromise conditions, including malignancy, HIV, diabetes mellitus, connective tissue disorders and those receiving corticosteroid treatment.11
Necrotising fasciitis is potentially a severe life-threatening condition with mortality reaching 25.3%.1 Contrary to the other five patients in our case review who survived, our patient went through an aggressive course with rapid progression to septic shock and multi-organ failure and died despite prompt active intervention.
Bacteraemia occurs in 27.2% of patients with necrotising soft tissue infections and increases mortality to 47.2% when present.1 Besides the presence of bacteraemia, mortality is also affected by delayed or inadequate surgery and degree of organ system dysfunction on admission.1
Because necrotising fasciitis evolves rapidly, heightened clinician awareness is needed based on appearance of the skin, swelling, extreme pain, fever and toxic appearance2,3 to ensure early diagnosis and rapid treatment. However, paucity of cutaneous findings early in the course of the disease makes diagnosis challenging. Blisters or bulla formation may be important diagnostic clue3 and when present signals the onset of critical skin ischaemia.
Once suspected, treatment should commence immediately with broad-spectrum intravenous antibiotics, early surgical debridement and supportive care in an intensive care unit. Since necrotising soft tissue infections are frequently polymicrobial, initial antibiotic cover should include agents effective against aerobic Gram-positive cocci, Gram-negative rods and a variety of anaerobes.
S enteritidis infection can lead to necrotising fasciitis and can be fatal, especially if associated with bacteraemia, multi-organ failure and septic shock. The possibility of this infection should be suspected in patients with an underlying immunosuppressive condition and monomicrobial Gram-negative infection.
LEARNING POINTS
A high index of suspicion is needed when dealing with cases of necrotising fasciitis.
Prompt and adequate treatment should be intuited to prevent mortality.
Monomicrobial cause of necrotising fasciitis is not uncommon and should be taken seriously.
Footnotes
Competing interests: none.
Patient consent: Patient/guardian consent was obtained for publication.
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