Recurrent mycotic aortic aneurysm with Klebsiella bacteremia and superimposed strongyloidiasis

Abstract

Mycotic aortic aneurysms are rare, representing <5% of all aortic aneurysms with limited epidemiological data. To date, there are only three case reports on mycotic aneurysm with Klebsiella pneumoniae infection including one case of recurrent infection. There are no case reports on mycotic aortic aneurysm in the setting of a Strongyloides stercoralis coinfection, a helminth associated with intravascular dissemination of enteric bacteria. Although an open repair strategy is considered a gold standard for the treatment of these aneurysms, there is some consideration for endovascular strategies in emergent scenarios. There is significant debate on the length of antibiotic treatment. Further, although in situ reconstruction is preferred, extra-anatomic revascularization such as axillobifemoral bypass may be warranted in the cases of extensive infection to allow complete resection of infected tissue. We report a unique case of recurrent mycotic aortic aneurysm with Klebsiella bacteremia and S. stercoralis coinfection managed with intrathoracic and intra-abdominal resection along with extra-anatomic axillobifemoral bypass.

Primary mycotic aortic aneurysms are rare, representing 0.7% to 4.5% of all thoracic and abdominal aortic aneurysms.¹ Among them, the rate of reinfection can be as high as 21% with a 46% to 70% mortality rate.² Most mycotic aneurysms are caused by Staphylococcus aureus or nontyphoidal Salmonella spp., accounting for 50% to 60% and 30% to 40% of cases respectively.¹ The remaining ∼10% of cases had a wide range of causative agents including enteric bacterial and fungal sources (especially among immunocompromised patients).¹ Only a handful of case reports have implicated K. pneumoniae as the causal organism of mycotic aneurysm,^3,4 whereas only a single case report from 2004 reports recurrent mycotic aortic aneurysm due to Klebsiella, in which case reinfection was attributed to antibiotic resistance in the particular strain.⁵ Interestingly, among patients with mycotic aneurysm at a health center in Taiwan there were six cases of Klebsiella bacteremia, for an incidence of 11.5%, far higher than the incidence reported in the Western countries.² This higher incidence is thought to stem from the prevalence of the hyperinfectious K1 and K2 capsular strains in this region, previously associated with disseminated infections such as liver abscess.⁶

S. stercoralis is an intestinal roundworm that is most prevalent in Southeast Asia, and unlike other helminths, S. stercoralis possesses the ability to maintain persistent infection through an autoinfective cycle.⁷ In most cases, the autoinfective cycle causes persistent infection with vague abdominal, respiratory, or skin symptoms. However, in some individuals, especially the immunocompromised, it may cause hematogenous dissemination of larvae. In such instances, the helminths directly seed distant sites such as lung, liver, and the central nervous system with enteric bacteria, leading to bacteremia.8, 9, 10, 11 Disseminated hyperinfection syndrome is strongly associated with bacterial sepsis, meningitis, multiorgan failure, and death.¹² Although Strongyloides is a well-described source of causing bacteremia, there have been no reports linking Strongyloides infection to mycotic aneurysm to date.

Definitive treatment for mycotic aneurysms requires both surgical resection for source control with either in situ or extra-anatomic reconstruction^1,13 and medical management with long-term or even lifelong suppressive antibiotics.¹ We describe a particularly virulent case of mycotic aneurysms of the thoracic and abdominal aorta from K. pneumoniae and Strongyloides that was also complicated by reinfection. The described patient provided consent for submission of this report.

Case report

The patient is a 70-year-old Asian man with a history of former tobacco use and chronic obstructive pulmonary disease. He presented with 10 days of ongoing fevers, chills, and abdominal pain, with a leukocytosis of 14.9/μL. Blood cultures were sent, and he received one dose of Vancomycin and Zosyn. Computed tomography angiography showed a small saccular outpouching of the infrarenal abdominal aorta with surrounding fat stranding and foci of air within the aortic wall concerning for mycotic aneurysm (Fig 1). Notably, the thoracic aorta appeared unremarkable on this scan.

Fig 1.

Initial computed tomography (CT) angiogram showing mycotic aortic aneurysm with associated foci of gas.

The patient was taken for emergent open repair via a transabdominal approach. Dissection was notable for heavy periaortic inflammation around the infrarenal aorta. The aortic wall was intact; however, it showed black discoloration with some air bubbles. There was no frank purulence. Tissue and culture swabs were sent. A 16 mm rifampin (goal ∼60 mg/mL)-soaked Dacron interposition graft was sewn in place with complete resection of the infected aortic tissue. The graft was covered with healthy retroperitoneal tissue. An omental flap was not performed given initial consideration of full resection of infected tissue and appropriate retroperitoneal coverage. Following case completion, the patient was extubated and taken to the intensive care unit.

The patient recovered from this initial operation well without major complication. Urine, blood, and intraoperative cultures grew K. pneumoniae and the patient was narrowed from broad-spectrum Vancomycin and Zosyn to Cefepime monotherapy. The specific strain of K. pneumoniae was not determined. Of note, blood cultures continued to be positive for 48-hours postprocedure. Our infectious disease colleagues also sent Strongyloides immunoglobulin G based on high index of suspicion due to the patient's previous residence in Asia. This returned positive a week later, and he was treated with a 2-day course of Ivermectin 200 μg/kg empirically for chronic helminth infection. The patient was ultimately discharged home on postoperative day 6 with a planned 6-week course of Ceftriaxone.

The patient experienced recurrent fevers 1 week after discharge associated with abdominal discomfort, with a leukocytosis of 13.4/μL despite his ongoing Ceftriaxone and completed Ivermectin treatment. Repeat computed tomography angiography showed perigraft air around the interposition graft as well as a new, presumed infected, penetrating aortic ulcer (PAU) measuring 1.5 × 2 cm in the descending thoracic aorta at the level of the diaphragmatic hiatus (Fig 2). The decision was made to manage the infected interposition graft first. The patient underwent a right axillobifemoral bypass, followed by excision of the infected graft with oversewing of the infrarenal and distal aortic stumps. The graft was surrounded by purulent fluid. The abdomen was copiously irrigated, and surrounding tissue was extensively debrided. An omental tongue was mobilized to cover the proximal aortic stump. Cultures from this reinfection again grew K. pneumoniae, but blood cultures and urine cultures were negative. He recovered well postoperatively. Interval imaging demonstrated stability of his presumed-infected descending PAU, and decision was made to allow the patient to recover before open thoracoabdominal aortic repair. He was discharged home on a 6-week course of intravenous Ertapenem, followed by planned indefinite antibiotic prophylaxis.

Fig 2.

Postoperative computed tomography (CT) angiogram showing (A) perigraft air and fluid, as well as (B) newly developed infected descending thoracic aortic ulcer.

One month later, he returned for open repair of his thoracic mycotic PAU through a standard left thoracoabdominal incision with takedown of the left diaphragm. This was done with single lung ventilation and without cardiopulmonary bypass. Our cardiac surgery colleagues provided intraoperative exposure assistance. The tissue surrounding the PAU was heavily inflamed, and the aorta was extremely friable. The infected portion was fully excised and reconstructed with a 28 mm rifampin-soaked gelweave graft. Cultures from intraoperative tissue samples produced no bacterial growth. Postoperatively, the patient recovered without major complication. He was discharged on postoperative day 15 with an additional 6-week course of intravenous Ertapenem. After that, he transitioned to lifelong Trimethoprim-Sulfamethoxazole with oral Vancomycin for Clostridium difficile prophylaxis.

In the 1.5 years since his final operation, he has recovered completely and returned to normal activity. Surveillance imaging at 1, 3, 6, and 12 months demonstrated intact repairs without concern for reinfection. He will undergo lifelong duplex monitoring of his axillobifemoral bypass.

Discussion

K. pneumoniae is rarely associated with mycotic aortic aneurysms,¹ and, to our knowledge, this is the first reported case that describes an associated S. stercoralis coinfection, which likely contributed to the severity of this case where the bacteremia seeded not one, but two separate areas of the aorta, in addition to a graft reinfection. This remains a theoretical link, although the natural history of S. stercoralis as a helminth capable of disseminating bacteria through hematogenous spread during the autoinfectious cycle without direct helminth tissue infection⁷ supports this mechanism.

K. pneumoniae is a part of normal gut flora in the estimated 16.3% of patients colonized by the bacteria.¹⁴ K. pneumoniae within the gastrointestinal tract could have acted as the reservoir for bacteria followed by dissemination by Strongyloides filariform larvae from the intestine to the blood stream. Our patient lived in Asia before arrival in the United States and thus could have played host to a particularly virulent strain of Klebsiella which is endemic to that region,^2,3,6 resulting in the severity of his infection. Similarly, given the lack of endemic Strongyloides in Massachusetts, our patient likely contracted his Strongyloides infection in Asia as well, which remained clinically indolent. We propose that clinicians have a high index of suspicion for Strongyloides coinfection when patients presenting with mycotic aortic aneurysm have resided or traveled to endemic regions including Southeast Asia and the Western Pacific. Similarly, patients with gram-negative bacilli, polymicrobial, or Streptococcus bovis bacteremia, which have been previously associated with Strongyloides^7,12 infection, warrant further investigation for this rare coinfection as well.

The index reconstruction of the mycotic aneurysm of the infrarenal aorta using rifampin soaked Dacron is a well-described method.^1,15 The rate of reinfection after repair with rifampin-soaked Dacron graft is estimated to be lower than 10% based on recent studies,15, 16, 17 though large-scale studies are lacking. The reinfection of this graft in our case is likely related to persistent bacteremia for 48 hours after the surgery despite appropriate antibiotic therapy. Vogel et al¹⁸ found that graft reinfection in those with persistent bacteremia was 4.2 times more likely compared with those without bacteremia. Some studies also suggest that rifampin is actually not effective against K. pneumoniae unless combined with polymyxin B or Colistin.19, 20, 21 Unfortunately, the emergent nature of this problem usually does not give us the luxury of waiting for bacteremia to clear or for speciation to occur.²² If suspicion is high for a virulent organism with persistent bacteremia, alternative conduits such as cryoartery or autologous femoral vein may provide better protection against reinfection,^1,15,23 and aggressive investigation with imaging or even reoperation may be warranted.¹ Although an index extra-anatomic revascularization strategy can be considered in similar scenarios, the emergent need for intra-abdominal control necessitated immediate intervention rather than initial extra-anatomic bypass. Further, the patient's persistent bacteremia may also have led to extra-anatomic graft infection as well.

Conclusions

Primary aortic mycotic aneurysms are rare but are associated with high morbidity and mortality and pose significant challenges in management. This case describes the ultimately successful treatment, both surgically and medically, of a unique coinfection with K. pneumoniae and S. stercoralis.

Funding

None.

Disclosures

None.