Case report

A 55-year-old man presented to a general surgical unit with a 3-day history of general malaise, fever and right iliac fossa pain. He had developed watery diarrhoea 3 weeks earlier and faecal culture had grown Salmonella typhimurium phage type 208 sensitive to ampicillin, ciprofloxacin, trimethroprim and gentamicin, but resistant to cefuroxime. He was managed conservatively by his general practitioner with resolution of symptoms prior to admission. His medical history included long-standing hypertension, an anterior myocardial infarction and quadruple coronary artery bypass grafting 6 and 8 years earlier, respectively, renal colic and a 5-cm diameter infrarenal abdominal aortic aneurysm. The latter had been diagnosed incidentally the year before during a hospital admission for pneumonia and an elective repair of this aneurysm had been cancelled when he was found to have poor left ventricular function. His medications were aspirin, diltiazem, enalapril, isosorbide mononitrate, frusemide and omeprazole. On examination his temperature was 38°C. Chest auscultation was normal and abdominal palpation revealed a tender but soft right iliac fossa and a non-tender aortic aneurysm. Initial investigation showed a haemoglobin of 11.0 g/dl, a white cell count of 8.5 × 10⁹/l with a normal differential, a C-reactive protein of 168 mg/l and an amylase of 77 IU/l. A chest X-ray showed right basal atelectasis and an abdominal ultrasound scan revealed a 5-cm diameter infrarenal aortic aneurysm. Echocardiography showed no evidence of endocarditis. Microbiological analysis of blood, sputum, faeces and urine were negative. He was initially commenced on intravenous cefuroxime 750 mg and metronidazole 500 mg, both tid.

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Figure Abdominal CT scan showing a leaking aortic aneurysm with retroperitoneal extension

On day 2 he became hypotensive with a blood pressure of 70/40 mmHg. A central venous line was inserted for fluid management and he was commenced on intravenous ciprofloxacin 400 mg bid. Abdominal computed tomography (CT) scans on days 2 and 5 showed no evidence of either a change in size or leakage from the aneurysm but did identify small bilateral pleural effusions and renal calculi. Despite continuing antimicrobial therapy he remained unwell with general malaise, and intermittent pyrexia and he developed severe left loin and iliac fossa pain. On day 13 he was transferred to the regional infectious disease unit where a bone scan showed isotope retention in the left ureter. Intravenous urography showed bilateral renal calculi and delayed emptying of the left ureter, and an abdominal CT scan confirmed an 8.5-cm diameter leaking aortic aneurysm with retroperitoneal extension causing compression of the left ureter (figure). Aortic aneurysm repair was performed using a straight celsoft/rifampicin graft. At operation the aorta and surrounding tissues were inflamed, oedematous and friable. Microscopy of the aortic wall revealed the presence of Gram-negative bacilli, although bacterial culture was negative. He was discharged home 27 days after admission. Oral ciprofloxacin 500 mg bid was continued for one month after discharge and at out-patient reviews since there has been no evidence of persistent infection. The clinical findings were consistent with a diagnosis ofSalmonella aortitis.

Discussion

Salmonella species are the commonest cause of bacterial aortitis accounting for one third of all cases.1 This reflects the incidence ofSalmonella infection in the community,2 the fact that 3–8% ofSalmonella infections result in bacteraemia,3 4 and the predilection of Salmonellae to infect damaged tissues such as atherosclerotic vascular endothelium.5 Patients are usually male, over 50 years old and may present in a variety of ways ranging from the typical features of a rupturing aortic aneurysm to pyrexia of unknown origin. There is often no history of gastroenteritis and back or abdominal pain in a patient with fever appears to be the most consistent feature.6 7 A pulsatile abdominal mass is palpable in only 42% of cases.7 In insidious presentations a high index of suspicion in the supervising physician is arguably the most important factor in making the diagnosis, which can be confirmed in most cases by CT scanning.8 As in our patient, the latter may not be diagnostic and repeat scans or further imaging may be necessary. Blood culture is positive in three-quarters of all cases ofSalmonella aortitis.6 7Optimum treatment requires early surgical intervention and an extended course of appropriate antimicrobial therapy, ciprofloxacin being the drug of choice for Salmonellainfections.6-9

The diagnosis of Salmonella aortitis in our patient was based on a recent history of Salmonellaenteritis in a patient with a pyrexial illness and a leaking aortic aneurysm. The diagnosis was confirmed by the finding of Gram-negative bacilli in the wall of the aorta and it is probable that blood and aortic wall cultures were negative because of the presence of antibiotics in these specimens. Treatment with omeprazole reduces gastric acidity and thereby increases the risk ofSalmonella infection.10 In addition, this patient was known to have atherosclerotic disease of the aorta and was therefore at increased risk of bacterial aortitis.5 We believe that general practitioners and hospital physicians should have a low threshold for prescribing antimicrobial therapy for the treatment of gastroenteritis in patients likely to have atheromatous disease of the aorta.

Even with modern surgical and antimicrobial management, the mortality of Salmonella aortitis exceeds 40%.6 7 This case demonstrates that in patients with an aortic aneurysm and pyrexial illness of unknown cause, bacterial aortitis should be quickly excluded.