CP2 - Staphylococcus aureus urine culture leading to diagnosis of psoas abscess; a case report
Abstract
Introduction
Staphylococcus aureus is the commonest pathogen causing psoas abscesses by hematogenous spread or local inoculation. Although commonly found in immunocompromised individuals, our case involves an immunocompetent patient who was diagnosed following a positive urine culture.
Case report
A 63-year-old male, previously unevaluated, presented in January 2025 with lower back pain worsening over one and a half months, interfering with his daily routines. More recently, the pain had started radiating along the right leg from the right buttock. He denied trauma or fever. His appetite had reduced, but he denied weight loss. He developed dysuria over the past two weeks, with poor urine flow and reduced output.
His right inguinal lymph nodes were palpable, and he could not raise his right leg above 80o due to pain.
His WBC count was 12.3 × 103/ µL with 83% neutrophils. His CRP was 67 mg/L, and ESR was 68mm/1st hour. X-ray L-S spine and Ultrasound scan (USS) abdomen were unremarkable. His urine culture became positive for >105 CFU/mL of methicillin-sensitive Staphylococcus aureus (MSSA), and he was started on IV ceftriaxone 2g daily. Blood cultures were subsequently requested, and two became positive for the same organism, despite being collected after antibiotics were commenced. IV flucloxacillin 2g was administered 6 hourly. His repeat USS revealed a right-sided psoas abscess; however, guided aspiration failed. Therefore, both antibiotics were continued, as the pathogen causing the abscess could not be confirmed. MRI of the L-S spine revealed paravertebral inflammation at the L3–L4 level, accompanied by a psoas abscess. The echocardiogram excluded infective endocarditis.
His pain gradually improved, and inflammatory markers decreased. We continued treatment for three weeks, monitoring the response clinically, biochemically, and radiologically. He was discharged on oral flucloxacillin with follow-up arranged through medical, microbiological, and neurosurgical reviews.
Discussion
Staphylococcus aureus can be a skin colonizer, and positive urine culture is often overlooked as a contaminant. However, it may indicate infective endocarditis or a deep-seated abscess and always warrants further investigation to rule out major pathology. In our patient, the presence of MSSA in the urine culture led to the diagnosis of a psoas abscess in the context of ongoing lower back pain, as it was properly investigated even in the absence of fever.
Downloads
