A Case of Infective Abdominal Aortic Aneurysm due to Haemophilus influenzae Type B

Abstract

Infective abdominal aortic aneurysm (IAAA) is relatively rare, but a case which is caused by Haemophilus influenzae type B is very rare. We experienced one IAAA case due to H. influenzae type B. The patient was 69-year-old man presenting with severe abdominal and back pain and elevated C-reactive protein (CRP), as inflammatory marker. The patient was found to have saccular aneurysm infrarenal aorta on computed tomography scanning. First, we started to treat him with antibiotic agent and second, we operated him at day 8 after admission with expanded polytetrafluoroethylene graft. Revascularization was made in situ reconstruction. As the result of culture with aneurysm wall, we found that the cause of this aneurysm was the infection of H. influenzae type B. As far as we know, this bacterium is scarcely reported as the cause of infective aortic aneurysms. We reported this IAAA case with the review of the English literature.

Infective or mycotic aneurysm is rare but a life-threatening disease. To our knowledge, the incidence of this disease is ~ 0.65 to 2% of all aortic aneurysms.^1,2,3 This disease has an increased tendency to grow rapidly and to rupture. Patients with this disease have severe comorbidities and coexisting sepsis. Conventional surgical treatment, which consists of a radical operation with resection of the aneurysm, extensive local debridement, and revascularization by in situ reconstruction or extra-anatomic bypass is the gold standard but carries a high mortality. Recently, some authors have described that endovascular aneurysm repair (EVAR) for infective abdominal aortic aneurysm (IAAA) was effective in perioperative and mid-term results.^3,4

Salmonella and staphylococcal species are predominant in the cause of IAAA, however, in this case, we detected Haemophilus influenzae. We reported this very rare case with the review of the English literature.

Case Report

A 69-year-old man had fever (over 39°C) and, 10 days later, he had severe abdominal and back pain. He consulted nearby doctor and was introduced to our hospital. At the time of initial examination, he did not have fever (36.7°C). On the physical examination, he complained of the spontaneous pain and tenderness at lower abdomen. In laboratory evaluation, white blood cell count and C-reactive protein (CRP) level were elevated, 9700/μL and 12.87 mg/dL, respectively. Furthermore, the level of glycated hemoglobin was 6.2% and he had mild diabetes mellitus. Blood culture result was negative.

Abdominal-enhanced computed tomography (CT) scan demonstrated a 35-mm saccular aneurysm of the infrarenal aorta surrounded by inflammatory findings (Fig. 1A–C). He was diagnosed as having IAAA. First, we treated him with intravenous antibiotic administration for a week. The antibiotic was cefazolin sodium (2 g/day) to cover staphylococcal and Salmonella species. Just before operation, the value of white blood cell count and CRP had decreased down to 6200/μL and 2.54 mg/dL, respectively. We thought that preoperative antibiotic therapy was effective. We performed operation on day 8 after antibiotic administration, and resected the saccular aneurysm with extensive local debridements and irrigation. Revascularization was made in situ reconstruction with expanded polytetrafluoroethylene graft, and entire prosthetic graft was covered with major omentum. Blood loss was estimated at 1200 mL. Patient received four units red blood cell transfusion during this operation.

Fig. 1.

Abdominal-enhanced computed tomography. This figure includes upper left site (A), lower left site (B), and right site (C). Upper left site demonstrates inflammation findings surrounding abdominal aorta and duodenum; lower left site and right site demonstrate false aneurysm. Its maximum diameter is ~ 35 mm.

Culture of the aneurysm wall was positive for H. influenzae type B. We changed the antibiotic to piperacillin sodium (2 g/day). During his hospitalization, the condition of this patient had been well. We started an oral antibiotic (levofloxacin hydrate 300 mg/day) at day 7 after surgical procedure, but the patient had mild elevation of renal function (the value of serum creatinine was 1.6 mg/dL).We switched the oral antibiotic from levofloxacin hydrate to minocycline hydrochloride (200 mg/day). At the day of discharge, day 22 (14 postoperative days), the level of CRP reduced to 0.23 mg/dL and serum creatinine was 0.78 mg/dL. After discharge, he had been administered minocycline hydrochloride for 2 months.

When he finished antibiotic administration, the level of CRP was 0.03 mg/dL, and the level of CRP has been normalized since then.

Discussion

Infective or mycotic aneurysm is rare but a life-threatening disease. To our knowledge, the incidence of this disease is ~ 0.65 to 2% of all aortic aneurysms.^1,2,3

Infective aneurysms are classified into five types:

1. Mycotic aneurysms secondary to septic arterial emboli, mainly endocardial in origin.

2. Microbial arteritis with an aneurysm secondary to bacteremic infection, nonendocardial in origin.

3. Infection pre-existing aneurysm.

4. The contiguous direct spread of infection to the arterial wall from an adjacent septic site.

5. Posttraumatic infected false aneurysm.^5,6

We think that this case is classified in type 2 because this patient had precedent fever without endocarditis and adjacent septic site, for example, psoas muscle abscess, pre-existing aneurysm, or posttraumatic state.

Infective aneurysms can affect almost any artery in the body. With the advent of invasive monitoring and interventional procedures, the femoral artery has recently become the most common location of all infected aneurysms (56%), followed in frequency by the thoracic and abdominal aorta (33%), intra- or extracranial (5%), innominate (2%), iliac (2%), and splanchnic arteries (1%).^5,6 Among the splanchnic arteries, the superior mesenteric artery is the most frequently involved, and the hepatic artery is the next most common site.^5,6

Generally, Salmonella and staphylococcal species are the most common agent for infective aneurysm.^5,6,7 In this case, against expectation, H. influenzae was detected. H. influenzae is a rarely reported causative agent, with a limited number of isolated case report.^7,8,9,10,11 Furthermore, Degener et al described that a documented case of H. influenzae type B has not been presented in the modern literature.⁸ As far as we know, we found only five cases of infective aneurysm due to H. influenzae which included type B, two cases; type F, one case; and unknown, two cases. H. influenzae is a gram-negative bacillus and may be capsulated or noncapsulated. Capsulation confers increased virulence, particularly serotype B. Serotype B are important cause of invasive infection in children, however, adult infection is less common and aortitis and subsequent aneurysm formation is extremely rare.^7,8

With regard to the diagnosis for this disease, arterial blood culture is necessary. If blood cultures are positive, they are helpful for the specific antibiotic therapy, but negative blood cultures do not rule out the presence of an infective aneurysm. Ultrasonography, CT including CT angiogram, and magnetic resonance imaging can be helpful.

When the diagnosis of this disease is established, first, we should start an adequate and strict medical treatment. Second, in surgical treatment, we should make complete resection of aneurysm and extensive debridement. In the past, extra-anatomic bypass had been performed in many cases.^10,12,13 However, vascular surgeons have been troubled the low rate of graft patency and the rupture of aortic stump. Recently, in situ reconstruction has been made using prosthetic graft or venous graft.^7,8,14 On the other hand, some authors described EVAR has been used for infective aneurysm.^15,16,17,18 Other authors described that 30-day mortality rate associated with endovascular therapy appears to be lower than that associated with open surgery.^3,4 However, in endovascular therapy, aneurysm is not resected and infection is continued. Some authors described EVAR, when patients present with rupture or have fever, could be used as a temporary measure to quickly achieve hemodynamic stability and as a bridging measure to possibly allow further definitive surgical treatment.^15,16,17,18

We think that classical medical and surgical treatment is essential and EVAR is an option for IAAA treatment.

Conclusion

We experienced a very rare case of IAAA caused by H. influenzae. We made an adequate treatment (medical and surgical) and thought that this strategy induced a good result.