Coxiella burnetii Aortitis Leading to Post-EVAR Vascular Graft Infection Complicated by Aorto-Colic Fistula: A Case Report with Literature Review

In the human body, the aorta is the main highway for blood, carrying life-giving oxygen from the heart to the rest of the system. When this massive vessel weakens and bulges, doctors often repair it by placing a synthetic tube, or graft, inside to hold the pressure. This is a life-saving procedure, but like any foreign object placed in the body, it carries a risk of infection. While most infections are caused by common bacteria that grow quickly in a lab dish, some are far more elusive. One such culprit is a microscopic organism called Coxiella burnetii, which causes a disease known as Q fever. This germ is unique because it hides inside the body's own immune cells, making it nearly invisible to standard tests that look for bacteria floating freely in the blood. When this hidden invader finds its way onto a vascular graft, it can create a slow, smoldering fire that eats away at the repair and the surrounding tissue, often leading to a catastrophic failure where the aorta bursts into the bowel.

The story of a 73-year-old man admitted to a hospital in Hangzhou, China, illustrates just how dangerous and difficult this specific type of infection can be. Three years earlier, the man had successfully undergone a repair for a bulging abdominal aorta. He had recovered well, but recently, he began suffering from recurring fevers and high levels of inflammation in his blood. Doctors tried standard antibiotics, but the fever did not go away. Because the man had a history of aortic repair, the medical team suspected that the graft itself might be infected, even though his blood tests showed no common bacteria growing. This is a common trap with Coxiella burnetii: it does not show up in the usual cultures used to identify infections. To find the source, the team used a special imaging scan that lights up areas of high activity in the body. The scan revealed a glowing, hot spot around the metal stent in his abdomen, along with pockets of gas that should not be there. This was a clear sign that the graft was infected and that the infection was severe enough to have created a hole, allowing gas from the intestines to leak into the area around the aorta.

The situation was confirmed when surgeons opened the man's abdomen. They found that the infected aortic graft had become stuck to the sigmoid colon, a part of the large intestine, and had formed a direct, dangerous connection between the two. This connection, known as an aortocolic fistula, meant that the barrier between the blood system and the digestive tract had collapsed. To save the patient, the surgeons had to perform a complex, emergency operation. They carefully removed the entire infected metal graft and the surrounding dead tissue. They then replaced the damaged section of the aorta with a new, synthetic tube that had been treated with an antibiotic to help prevent future infection. Because the colon had been breached, they also had to repair the hole in the intestine and create a temporary opening for waste to exit the body, allowing the area to heal without being contaminated by stool.

After the surgery, the team turned to the laboratory to identify the exact cause of the infection. Standard blood tests had failed, but a specialized test that looks for antibodies, which are the body's defense proteins, revealed the truth. The man's blood showed high levels of antibodies against Coxiella burnetii, confirming that Q fever was the culprit. Interestingly, the level of antibodies was lower than what doctors usually expect to see in a chronic infection, but the combination of the surgery findings and the imaging scan made the diagnosis certain. This case highlights a critical lesson for medical professionals: when a patient with a vascular graft has a fever that won't go away and standard tests come back empty, doctors should consider this hidden germ even if the antibody numbers are not at the traditional high threshold. The infection had been hiding in plain sight, masked by the body's own defenses and the difficulty of detecting it.

The treatment plan for this patient went beyond just the surgery. Because Coxiella burnetii lives inside cells, it requires a specific, long-term approach to be fully eliminated. The patient was started on a combination of two medications: doxycycline and hydroxychloroquine. This pair works together to change the environment inside the cells where the germ hides, making it possible for the antibiotic to kill the bacteria. The doctors explained that this treatment would need to continue for at least a year and a half to two years to ensure the infection was completely gone. The patient responded well to the surgery and the medication. Follow-up scans showed that the new graft was working perfectly, with no signs of the infection returning or the blood vessel leaking. His fever disappeared, and his blood markers returned to normal.

This case report serves as a guide for how to handle these rare and tricky infections. It shows that relying solely on old rules about how high antibody levels must be can lead to missed diagnoses. Instead, doctors must look at the whole picture: the patient's symptoms, the results of advanced imaging, and the findings from surgery. When these pieces fit together, even with lower-than-expected antibody numbers, the diagnosis of a persistent Q fever infection can be made. The path to recovery involves a team of specialists working together to remove the infected material, rebuild the blood vessel, and then commit to a long course of targeted medication. For the 73-year-old man, this multidisciplinary approach meant the difference between a fatal outcome and a full recovery, proving that even the most stubborn infections can be defeated with the right combination of surgery and science.