Mycotic Aneurysm of the Infrarenal Abdominal Aorta Caused by Campylobacter fetus Identified After 10-Day Antibiotic Therapy

We report a rare case of a mycotic aneurysm caused by <i>Campylobacter fetus</i>, undetectable by Gram staining or surgical specimen culture obtained after 10 days of antimicrobial therapy. However, the pathogen was successfully detected by 16S rRNA gene sequencing. An 83-year-old woman with comorbid hypertension presented with lumbar and lateral abdominal pain and was diagnosed with an abdominal mycotic aneurysm. Despite its low sensitivity for a negative Gram staining test and culture-negative specimens, 16S rRNA gene sequencing can identify the causative organism and facilitate appropriate antibiotic therapy.