A Case of Abdominal Aortic Aneurysm Caused by <i>Helicobacter cinaedi </i>

Helicobacter cinaedi is a gram-negative spiral bacillus. The bacterium is known to cause opportunistic infections in immunocompromised hosts with blood cancer or HIV infection, but infected aneurysms caused by H. cinaedi are very rare. Herein, we report the case of a patient with an infected abdominal aortic aneurysm (AAA) caused by H. cinaedi. A man in his 60s complained of abdominal pain. He had the history of AAA and thoracic aortic aneurysm treated with graft replacements, respectively. Findings of abdominal computed tomography (CT) led to the suspicion of an AAA with impending rupture, and the patient was admitted to our hospital. On admission, laboratory tests revealed marked elevation of the serum levels of inflammatory biomarkers. An infected AAA was suspected and specimens were obtained for blood culture. The patient was started on treatment with doripenem (DRPM) plus daptomycin (DAP). However, the results of blood culture obtained three days later revealed gram-positive spiral bacilli, and DAP was switched to levofloxacin (LVFX). H. cinaedi was identified by Matrix Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS). On day 7 after admission, CT revealed an increase in the size of the AAA, suggesting an even higher risk of rupture. Therefore, laparotomy was performed for abdominal aortic replacement with a prosthetic graft. Since the antimicrobial susceptibility testing revealed that the H. cinaedi was resistant to LVFX, LVFX was discontinued after the operation. The postoperative course was uneventful and the patient was transferred to another hospital for further management on day 33. He had received antibiotics for six weeks. We confirmed H. cinaedi as the causative bacterium by genetic analysis of tissue samples obtained from the resected AAA, and the patient was diagnosed as having had an infected AAA caused by H. cinaedi. Although genetic analysis is the gold standard to identify H. cinaedi, MALDI-TOF MS is also useful. Thus, H. cinaedi should be considered as one of the possible causative pathogens in patients diagnosed as having infected aortic aneurysms.