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Q1: What is the single most important investigation?
Multiple blood cultures. Blood cultures grew Salmonella enteritidis in this patient.
Q2: What is the diagnosis?
Mycotic aneurysm of the common iliac artery. The history of self limiting episodes of diarrhoea and vomiting should make one to suspect salmonella mycotic aneurysm.
Q3: What are the risk factors for this complication?
The commonest risk factors for salmonella mycotic aneurysms are age greater than 50 years, atherosclerosis, diabetes mellitus, and immunocompromised states especially AIDS. Besides the age, there were no other risk factors in this patient.
Salmonellae are non-encapsulated, non-sporeforming Gram negative rods whose classification continues to evolve. All salmonellae but one (Salmonella bongori) are widely believed to be members of a single species S enterica which is further divided into seven groups considered as subspecies encompassing on a whole at least 2324 serovars.1
Salmonellosis may manifest in five different clinical forms including asymptomatic chronic carrier state, gastroenteritis, enteric fever, bacteraemia, and extraintestinal localised complications of which endovascular infection is one of the most serious.
Though S typhi and S paratyphi infect only humans and cause enteric fever and chronic carrier state, non-typhoidal salmonella are widely spread in nature and affect all age groups causing gastroenteritis, bacteraemia, and extraintestinal localised complications. Despite high standards in food processing, contaminated food products remain the main source. In a recent study of non-typhoidal bacteraemia, adults were more likely to have predisposing factors and a high incidence of extraintestinal organ involvement and a high mortality.2
The diagnosis of vascular infection due to salmonella requires a high index of suspicion.
Assessment should be done urgently as resultant aneurysms may rapidly expand and rupture.
Mycotic aneurysms are localised dilatations of arterial wall that develop secondary to an infective process spreading either contiguously from an adjacent source of infection or more commonly haematagenously. The incidence of 10% for endovascular complications in salmonella bacteraemia in patients over 50 years is consistent across three studies.2–4 The commonest predisposing factors for salmonella mycotic aneurysms are age greater than 50 years, atherosclerosis, diabetes mellitus, and immunocompromised states especially AIDS. The clinical course can be acute, subacute, or chronic and cases of aneurysm have been reported even after six months of primary infection. Almost every arterial site in the body may be involved; however, infections of the aorta especially the infrarenal segment appear to be the most frequent. Nearly all instances of salmonella aortitis result in aneurysm or more rarely enlargement of a previously existing aneurysm. The diagnosis of vascular infection due to salmonella requires a high index of suspicion, and the important clues are listed in the box 1.
Box 1: Clinical clues for vascular infection with salmonella
Prolonged fever after an episode of gastroenteritis.
Recurence of salmonella bacteraemia during or after adequate treatment.
Pain in the back, abdomen, or chest accompanied by salmonella bacteraemia.
Vertebral spinal involvement with salmonella bacteraemia.
Salmonella bacteraemia in patients with prosthetic vascular grafts.
The assessment should be done urgently in order to reduce morbidity and mortality as the aneurysms may rapidly expand and rupture. The method of choice for diagnosing infected aneurysms appears to be computed tomography of the chest and abdomen. Surgical resection should soon follow the start of effective antimicrobial therapy, which is mainly with quinolones or third generation cephalosporins. Although in situ repair has been reported as successful in some patients,5 restoration of blood flow by extra-anatomical bypass with or without subsequent reconstruction seems to lead to improved short and long term prognosis. Although no consensus exists on the length of postoperative antibiotic treatment, it should be for at least six weeks and may be for life in immunocompromised individuals.6
Salmonella mycotic aneurysm of the common iliac artery.