Mycotic aneurysm as a result of severe salmonella infection in the adult intensive care unit: two case studies.

Abstract

Salmonella infections are relatively common and are generally associated with contaminated food products. Common clinical manifestations include fever, bacteremia, and chronic permanent asymptomatic colonization of the bowel (Schneider, Krulls-Munch, & Knorig, 2004). However, a small percentage of all patients with salmonella bacteremia may present with vascular infections in the form of an aneurysm (Cohen, O'Brien, Schoenbaum, & Medeiros, 1978; Shimoni et al., 1999). While it is extremely rare for those who work in the intensive care unit (ICU) to care for such patients, it is essential for health care professionals to recognize this disease in order to make a rapid diagnosis to prevent complications, such as mycotic aneurysm. This article is framed around two patients who presented to the same ICU following surgical intervention. The etiology of salmonella bacteremia, mycotic aneurysm, the risk factors, diagnosis, and treatment are discussed.

Salmonella infections are relatively common and are caused by contaminated food products, such as those made from chicken and pigs, and can cause gastroenteritis in humans. Common clinical manifestations of enteric salmonella include fever, bacteremia, and chronic permanent asymptomatic colonization of the bowel (Schneider, Krulls-Munch, & Knorig, 2004). Approximately 10% of all patients with salmonella bacteremia present with vascular infections, often in the form of an aneurysm (Cohen, O'Brien, Schoenbaum, & Medeiros, 1978; Shimoni et al., 1999). This discussion is framed around two patients who presented to our intensive care unit (ICU). One patient was admitted following repair of a ruptured popliteal aneurysm and repair of an abdominal aortic aneurysm. The other patient was admitted to the ICU after a mitral valve replacement secondary to salmonella bacteremia. Both patients are presented and the etiology of salmonella bacteremia, mycotic aneurysm, the risk factors, diagnosis, and treatment are discussed.

Case presentation one

A 72-year-old male presented to a local rural nursing station with a flu-like illness. After two more weeks, he presented to a local hospital with ongoing diarrhea. At the hospital, he was diagnosed with salmonella endocarditis. He was admitted to the ICU where he was treated with antibiotics, fluids, and mechanical ventilation briefly. After transfer to the ward, swelling of the left knee and pelvis was noted by the nurses. The patient was transferred to a large, tertiary care hospital in the nearest city for surgical repair of a ruptured left popliteal aneurysm with vein bypass, repair of an iliac aneurysm, and revision of an abdominal aortic aneurysm. After surgery he was admitted to the surgical ICU with a diagnosis of repair of septic mycotic aneurysms secondary to salmonella endocarditis and Strep B. gastroenteritis.

Case presentation two

A 68-year-old female presented to a medical clinic with complaints of lower back and abdominal pain. Her symptoms were consistent with an abdominal aortic aneurysm and she was transferred to a large tertiary hospital for further investigation and treatment. ACT scan revealed an aneurysm of the distal portion of the abdominal aorta and it was noted "mycotic aneurysm, although possible, is very much less likely" as the cause of the aneurysm. She was sent home to await surgery after it was determined that she did not require emergency surgical intervention. After three weeks, she returned to the same hospital's emergency department with a two-day history of weakness and diarrhea. She was diagnosed with flu-like illness and sent home.

The patient presented to a community hospital emergency department after two weeks with complaints of weakness and diarrhea and was immediately transferred to the large tertiary hospital where she was admitted to a surgical ward. Further investigation revealed a 3.4 cm mycotic aneurysm in the abdominal aorta. In addition, a lesion was noted on her mitral valve, and it was determined that the patient had salmonella endocarditis with a rheumatic mitral valve, in addition to the abdominal aortic aneurysm.

Salmonella

Infections due to salmonella are common, and the incidence has increased markedly in many countries of the world. There are more than 2,000 serotypes, and some, such as salmonella typhi and salmonella paratyphi, infect only humans (Chiu, Su, & Chu, 2004). In the United States, nontyphoid salmonella affects approximately two to three million people per year, can cause 500 to 2,000 deaths each year (Altekruse, Cohen, & Swerdlow, 1997), and is most often associated with certain animals, such as chickens. In fact, nontyphoid salmonella is a major cause of food-borne infection worldwide (Chiu et al., 2004). It can cause significant morbidity and mortality. Infections of this type often result in self-limited acute gastroenteritis that does not require antibiotics; however, approximately five per cent to 10% of individuals who contract nontyphoid salmonella develop bacteremia. Asymptomatic chronic carrier state, gastroenteritis, enteric fever, bacteremia and localized extra-intestinal complications, such as endovascular infection, are the five different clinical forms that Salmonellosis may manifest (Benenson et al., 2001). In addition, salmonella may involve almost every arterial site in the body.

There are a number of factors that may place a person at risk for such extra-intestinal infections such as meningitis, endocarditis, pyomyositis, osteomyelitis and vascular infections (Schneider et al., 2004). Those with underlying malignancies, liver cirrhosis, systemic lupus erythematosus, receiving immunosuppressive therapy, HIV infection and AIDS, inflammatory bowel disease, extremes of age, diabetes, and previous use of corticosteroids appear to be at risk for more serious complications of salmonella (Chen et al., 1999; Chiu et al., 2004; Hsu, Chen, & Chu, 2004).

Mycotic aneurysm

One of the most feared complications of salmonella is the development of infectious endarteritis, which is also known as infectious aortitis or mycotic aneurysm. The term mycotic aneurysm was first coined by Canadian Sir William Osler in 1885, and described as "an abnormal dilatation of an arterial wall induced by bacterial or mycotic infection" (Osler, 1885, p. 467). It was later used to describe the septic emboli in patients with infective endocarditis that carry embolic materials to distal arterioles where they cause obstruction or attach to the vessel walls, causing further inflammation and destruction of the vessels involved. This leads to a mushroom-shaped aneurysm (Chiu et al., 2004).

Primary mycotic aneurysms occur because circulating bacteria become implanted on a damaged area of the aortic intima. Salmonella with streptococci and staphylococci are among the most common bacteria detected in mycotic aneurysms. Patients who have pre-existing atherosclerotic disease are more likely to develop mycotic aneurysms in the presence of salmonella because of the bacteria's ability to invade normal arterial intima. Andreasen, Dimcecski and Nielsen (2001) state that aneurysms are believed to be infected by three different mechanisms: 1) septic arterial emboli, 2) infections extending through lymphatic vessels from an adjacent infection, or 3) seeding of the arterial wall during bacteremia from a distant focus. In the past, mycotic aneurysm caused by salmonella was usually fatal. The overall mortality of a salmonella-induced mycotic aneurysm is now reported to be between 53% and 60% (Schneider et al., 2004).

Diagnosis

Depending on their location, aneurysms may remain undiagnosed until they eventually expand and rupture, further increasing the morbidity and high rates of mortality (Benenson et al., 2001). Salmonella may be suspected in cases where there is a high recurrence of bacteremia. Prolonged fever and back and abdominal pain are among the most commonly reported symptoms of those with mycotic aneurysms. In the elderly, fever and abdominal pain with a history of previous diarrhea should suggest the diagnosis. Ideally, a diagnosis should be established as quickly as possible to reduce mortality. However, these infections are relatively uncommon, with approximately 150 reported cases in the literature as of 1999 (Fernandez Guerrero, Aguado, Arribas, Lumreras, & de Gorgolas, 2004), making it quite unlikely that institutions have significant experience with extreme cases of salmonella, and this further compromises mortality.

Once suspected, transesophageal echocardiogram (TEE), Gallium-67 scan, and ultrasound may be used to confirm the diagnosis. MRI and angiography are also useful in delineating the saccular nature of mycotic aneurysm. One advantage of MRI may be the ability to image multiple layers, which allows for soft tissue contrast. Echocardiography, angiography and CT could all be used to obtain the same information as the MRI; however, CT scan with contrast enhancement is considered the method of choice, as it allows for early detection of changes in the arterial wall and periaortic tissue and is relatively more accessible than MRI (Benenson et al., 2001; Chiu et al., 2004; Fernandez Guerrero et al., 2004).

Treatment

Once the diagnosis of mycotic aneurysm has been made, prompt treatment is essential. Antibiotic treatment must be initiated for the salmonella-induced aortitis. Fluoroquinolones, like ciprofloxacin, given intravenously are recommended until the susceptibility pattern of the infective organism is known. Although there is no consensus as to optimal length of therapy for endovascular infections, the most commonly cited recommendation is a minimum of six weeks (Chiu et al., 2004; Cohen et al, 1978; Fernandez Guerrero et al., 2004; Gufler, Buitrago-Tellez, Nesbitt, & Hauenstein, 1998; Schneider et al., 2004). In addition, surgical resection of the endovascular infection is important as this appears to restore blood flow leading to improved short- and long-term prognosis (Benenson et al., 2001).

Nursing care

Care of the patient with mycotic aneurysm secondary to salmonella hinges on frequent assessment. Assessing the patient's level of pain, including the severity and location is important as pain is one of the most common symptoms with arterial occlusion. The pallor or absence of pallor of the dependent limbs, pedal pulses, the temperature of the extremities, and the ability to move limbs must be assessed as well.

The patient and family must be taught proper food handling and storage, and the necessity for hand hygiene to prevent further contamination. Smoking cessation and further risk factor reduction strategies such as diet education and blood sugar control should be initiated while the patient is hospitalized and follow-up by the family physician or, in this case, the nursing station should be encouraged.

Case study one continued

Our patient had a past medical history that included ischemic heart disease, aortic stenosis, smoking, and COPD. He had had a myocardial infarction 20 years earlier, was a 100-pack per year smoker and reported drinking between six and 10 beers and one to four ounces of hard liquor per day. On arrival to our ICU, he was cardioverted for atrial fibrillation. The pain in his right leg was increasing and he was taken to surgery overnight for repair of a ruptured popliteal aneurysm, iliac aneurysm and abdominal aortic aneurysm. A left axilla bifemoral bypass with ligation of the hepatic right common iliac artery aneurysm, ligation of the infrarenal aorta, and ligation of the left common iliac artery were performed by the vascular surgeon. His WBC on admission was 15.1 (normal = 4.8 to 10.8) and peaked at 25.3 by post-operative day one. His blood cultures indicated salmonella Group B. He had been started on antibiotics according to the infectious diseases consultant's recommendations, was ventilated, and was receiving small doses of neosynephrine. He was to be weaned from the ventilator and inotropes as tolerated. On post-operative day one, absence of pedal pulses was noted bilaterally. He returned to the OR for evacuation of a clot from the left femoral graft. He returned to the OR again the next day for a right femoral/popliteal bypass because of an ischemic right leg.

On post-operative day four, the patient was transferred to the stepdown unit, and was finally discharged to his local hospital. The remainder of his clinical course was uneventful and he was eventually discharged home.

Case study two continued

While on the surgical ward awaiting repair of the abdominal aortic aneurysm, the patient developed a fever and signs of heart failure. An echocardiogram showed a large lesion on the mitral valve. Based on the location of the abdominal aneurysm, a mycotic aneurysm could not be excluded as the cause. The patient was treated with cefotaxime and ciprofloxacin. Her hemoglobin was low and she was transfused with two units of packed red blood cells. There appeared to be increased clotting to her left popliteal artery and she was treated with anticoagulants. After eight days, she continued to be febrile intermittently, and exhibited signs of right heart failure. In addition, the patient began to complain of visual disturbances. By day 12, she was blind in her left eye, likely due to embolic events, and had suffered a splenic infarction. In addition, her left leg was ischemic because of popliteal emboli, and the aneurysm had expanded and was now an aortic iliac mycotic aneurysm. It was determined that surgical repair of the mitral valve was required despite surgical risks related to the infection. The patient underwent surgery for mitral valve replacement for endocarditis secondary to salmonella bacteremia. She was transferred to the stepdown unit one day after surgery. She underwent surgery for repair of her aneurysm one week after her initial admission and the remainder of her clinical course was uneventful. She did not regain vision to her left eye. As a teacher, this was an impact upon her quality of life, as well as her functional ability.

Conclusion

While salmonella infections are relatively common and are associated with contaminated food products, it is relatively rare for those who work in the ICU to care for such patients. The extreme complications, such as those affecting the vascular system can be life-threatening, and the impact potentially devastating for the patient and family. It is essential for health care professionals to recognize the disease in order to make a rapid diagnosis. Early treatment must be initiated to prevent complications such as mycotic aneurysm. This disease is relatively rare in ICU settings, but with knowledge and education of both the health care professionals and the public, salmonella and the devastating complications could be virtually eliminated.

References

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By Asha A. Pereira, RN, BA, BN, CNCC(C), Nursing

Educator, Cardiac Sciences Program, St. Boniface General

Hospital, Winnipeg, MB