Escherichia coli-Induced Aortitis and Aortic Perforation: A Case Study and Literature Review

Introduction

Aortitis refers to inflammation of 1 of the 3 layers of the aortic wall [1]. While non-infectious diseases account for the majority of cases [2], infectious aortitis is less common but life-threatening [2,3]. In normal situations, the aorta is not susceptible to infection; however, certain factors increase the risk of infectious aortitis, such as vascular anomalies, medial cystic necrosis, atherosclerosis, and aortic implants and prostheses. In addition, diabetics and older men over 50 have a higher risk of developing infectious aortitis [1,3].

Aortic infections commonly result from bacterial seeding of atherosclerotic plaques, contiguous spread from nearby infections, or trauma (penetrating or closed) that facilitates microbial entry. Other causes include septic emboli in the aortic vasa vasorum and vascular manipulation, with the abdominal aorta affected in about 2/3 of cases [4,5].

A variety of pathogens have been implicated, including bacteria and fungi. In the pre-antibiotic era, bacterial endocarditis (including Treponema pallidum, the cause of syphilis) was the most common underlying cause [4]. Currently, both Gram-positive bacteria, such as staphylococci, streptococci, and enterococci, and Gram-negative bacteria are well known causative agents of aortitis [4–6]. Other microorganisms such as Mycobacterium tuberculosis, and fungi like Candida and Aspergillus are rare causes of infectious aortitis [4,5]. Gram-negative bacilli are less frequent causes of infectious aortitis. In the literature, Salmonella and Pseudomonas species are the most commonly reported bacteria causing aortitis [7]. In contrast, Escherichia coli is a rare etiological agent [8], primarily documented through isolated case reports and small series [8–36].

Some reports have indicated that infections caused by Gram-negative organisms are linked to a higher incidence of suprarenal aneurysms, rupture, and elevated morbidity and mortality rates [7]. While infections in pre-existing aneurysms are typically infrarenal, infections in an atheromatous aorta more often result in suprarenal aneurysm formation, presenting greater management challenges [7].

We describe a patient with E. coli aortitis and review published cases, seeking to identify the specific characteristics and clinical outcomes associated with E. coli aortitis. This analysis explores distinctions between E. coli and other Gram-negative organisms in aortitis presentations, highlighting implications for clinical management based on insights from the literature.

Case Report

LITERATURE REVIEW:

We were able to retrieve case reports from 33 patients diagnosed with E. coli aortitis [8–35] (Table 2). Of these 33 patients, 26 were male (79%), and their mean age (±SD) was 69±11 (range 41–85) years. The CT was the predominant diagnostic method used, in 31/33 (94%) cases, accompanied by occasional use of ultrasound and magnetic resonance angiography (MRA) for specific instances. The majority (27/33, 82%) required surgical intervention, including aneurysmectomy (6/33), various bypass procedures (6/33), EVAR in 4 cases (of which 1 involved thoracic EVAR), resection/aortectomy with graft (11/33, 33%), a stent-graft procedure in 1 case, and innovative approaches in solitary cases, like in situ repair with aortic homograft and in situ implantation of a rifampin-soaked prosthetic graft.

All patients were treated with intravenous antibiotics, involving a range of antibiotics according to the individual pathogen’s susceptibility. There is little information in the reports on total duration of antibiotic treatment, especially for intravenous treatment. Of the 32 patients for whom survival data were available, 7 patients died (22%). Of these 7 patients, for 2 of the patients, from 1978, it was not reported whether they received surgical intervention [10]; 2 patients did not receive surgical intervention because of significant co-morbidities [18,29]; 2 patients had open resection and graft placement [28,31]; and 1 patient who received EVAR (out of a total of 4 patients who received EVAR) died, as reported by us. Overall, 3/27 (11%) of the patients who received some kind of surgical intervention died. In contrast, 2 out of the 4 patients (50%) who did not receive any surgical intervention died (P<0.05).

Discussion

Our review of published cases of E. coli aortitis spans from 1978 to 2023. Several features are noteworthy; first, although there is a significant age range, there is a notable trend toward older individuals. This predilection for older age can probably be attributed to the increasing prevalence of atherosclerosis with age [37]. Various studies and clinical observations have documented a correlation between age, atherosclerosis, and susceptibility to infectious aortitis in general [3,20,38]. For example, a study published in 1989 reviewed 21 cases of bacterial aortitis involving diverse organisms over a 10-year period. The median age of the patients was 65 years, which closely resembles the median age of 69 years observed in our study (see Table 2) [10].

The second noteworthy feature involves sex. Although E. coli aortitis may affect both men and women, there appears to be a significant male preponderance (26/33, 79%). A 2009 literature review showed that infectious thoracic aortitis predominantly affects males, showing a male-to-female ratio of 3: 1, with a mean age at diagnosis of 65 years [6]. This male predominance also may be influenced by the higher prevalence of abdominal aortic aneurysm in men, which is largely driven by risk factors such as smoking, hypertension, and atherosclerosis [39]. Since infective aortitis involves the abdominal aorta in about 2/3 of cases, these epidemiological and vascular risk factors likely contribute to the observed male predominance [40].

Third, diagnostic imaging is critically important for early diagnosis, facilitating prompt initiation of antibiotics and surgical intervention. Of the various diagnostic modalities, CT scan is evidently the optimal diagnostic method. CT scans assess the thickness and regularity of the aortic wall, measure aortic diameter, detect mural calcifications, and evaluate the condition of aortic branches, with crucial information regarding aortic dilation, aneurysm formation, and abscesses. The ability of CT to visualize vascular structures and surrounding tissues aids in the accurate diagnosis and characterization of E. coli aortitis [41]. Positron emission tomography (PET)/CT imaging is an evolving diagnostic instrument in the management of aortic disorders, with an emphasis on the evaluation of aortitis. Its dual capability to visualize the aorta’s structure, detect inflammation and metabolic activity via fluorodeoxyglucose uptake, and provide insight into disease activity and progression may contribute to improved outcome of patients with aortitis [42].

Fourth, surgical treatment of aortic diseases, as shown in Table 2, consists of diverse approaches tailored to the severity and extent of the condition. Over the years, the surgical management of aortic diseases has undergone significant change: from the traditional open surgical technique, including aneurysmectomy and bypass procedures, to the more recent endovascular approaches, such as EVAR and thoracic endovascular aortic repair (TEVAR).

Treatment of infectious aortitis requires a multidisciplinary approach that combines surgical intervention with long-term antibiotic therapy. The choice between endovascular and open surgical repair is often determined by the extent of infection, aneurysm characteristics, and patient-specific factors [43].

Despite the traditional preference for open surgery due to concerns over stent infection and complications, endovascular procedures such as EVAR and TEVAR have become increasingly prevalent in the management of aortic diseases due to their less invasive nature and reduced perioperative risk [44]. In 2021, Han and colleagues conducted a systematic review and meta-analysis comparing outcomes between endovascular and open repair techniques for treating infective native aortic aneurysms [45]. Their comprehensive study aimed to evaluate the effectiveness and safety of both approaches in managing aortitis. They found that while EVAR offers better short-term survival, it is associated with a higher risk of infection-related complications compared with open surgical treatment. No significant differences were observed in long-term mortality or the need for reintervention between the 2 methods. EVAR is suggested as an alternative for low-risk patients or those at high risk with open surgery [45]. As shown, 3 of 4 patients treated with EVAR since 2012 completely recovered, while our patient was evidently the only one with relapsed infection and recurrent abscess formation that required open surgery.

This poor outcome may reflect the elevated risk of infection-related complications associated with EVAR in high-risk patients, as reported by Han et al, particularly given our patient’s advanced age, diabetes, extensive atherosclerosis, and the presence of ongoing infection at the time of graft placement – all of which likely contributed to relapse and the eventual need for open surgical intervention. Persistent infectious foci within the diseased aortic wall may have been inadequately treated due to limited antibiotic penetration. The timing of EVAR during active bacteremia may have enabled bacterial colonization and biofilm formation on the graft. Additionally, the duration of intravenous antibiotic therapy may have been insufficient, as prolonged treatment is often required in complex cases like this. This is especially important given that oral cefuroxime has poor and variable bioavailability, which can lead to significant interindividual variability in pharmacological response and reduced therapeutic efficacy compared with intravenous administration [46]. Therefore, in retrospect, intravenous antimicrobial treatment should possibly have been continued for 6 to 12 weeks, although it is unclear whether this would have positively influenced the patient’s outcome.

Finally, in contrast to the high mortality rates (21–44%) reported with other Gram-negative aortitis [38], documented cases of E. coli aortitis show a significantly higher survival rate. The reason for this discrepancy is not clear: E.coli is hardly less lethal than other Enterobacterales. Possibly, this reflects a publication bias: in recent years, a higher percentage of patients with E. coli aortitis were treated compared with patients with aortitis due to other Gram-negative bacilli. This suggests improved medical and surgical management, though the lack of long-term survival data does not allow for determination of long-term outcome [20].

The present study has several limitations. Firstly, a case series which combines data from many different papers, may suffer from inconsistent data, or insufficient clinical information. One crucial missing piece in the puzzle consists of a lack of information on the optimal duration of intravenous antibiotic treatment. Due to the adverse outcome for our patient, we are inclined to recommend at least 6 weeks of intravenous antimicrobial therapy, which, according to follow-up CT findings and inflammatory markers, could be extended to 8 or 12 weeks. Secondly, there may have been a publication bias, as authors and journals may prefer publication of case reports or series of patients who survived. Finally, this review is limited by the small sample size of reported cases, the retrospective nature of the included studies, and the inherent selection bias in the literature, which may limit the generalizability of our findings.

Conclusions

In conclusion, we described an 82-year-old man with E. coli aortitis, who was treated with intravenous antibiotics and EVAR, and reviewed 32 previously published cases of E. coli aortitis with a mean age of 69±11 and male predominance (26/33, 79%). The main diagnostic modality was the CT scan (27/31, 87%). In addition to prolonged, parenteral antibiotics, surgical intervention was associated with significantly improved outcome (24/27, 89%). From our case report, we suggest that prolonged intravenous antibiotic treatment for at least 6 weeks, extending to 12 weeks in complex cases, is required. This recommendation is particularly relevant for antibiotics with variable oral bioavailability. Additionally, frequent imaging studies are necessary, and PET scans could be considered for follow-up to search for residual infection, particularly in cases involving virulent infections like E. coli, which possesses the ability to form biofilms and remain for longer periods. Thus, prolonged treatment is required to prevent complications and recurrence.