Workup for Staphylococcus epidermidis UTI
When S. epidermidis is isolated from urine culture in a symptomatic patient, you must actively investigate for underlying urological abnormalities or predisposing factors, as this organism is a true uropathogen in these contexts, not merely a contaminant.
Initial Assessment
First, confirm this is a true infection rather than asymptomatic bacteriuria or contamination:
- Verify symptoms are present: dysuria, frequency, urgency, suprapubic pain, flank pain, fever, or systemic signs 1
- Obtain proper urine culture: Ensure the specimen was collected appropriately (clean catch or catheterized sample) with colony counts documented
- Assess for systemic involvement: Check for fever, chills, costovertebral angle tenderness suggesting pyelonephritis 2
Mandatory Imaging and Anatomical Evaluation
The literature consistently demonstrates that S. epidermidis UTIs occur in patients with structural abnormalities. You must perform imaging to identify underlying pathology 3, 4, 5:
Imaging Studies to Order:
Renal and bladder ultrasound - first-line to detect:
- Hydronephrosis
- Nephrolithiasis (commonly associated with S. epidermidis UTI) 2
- Bladder abnormalities
- Incomplete bladder emptying
Voiding cystourethrogram (VCUG) - particularly in children to evaluate for:
- Vesicoureteral reflux (frequently found in pediatric cases) 5
- Posterior urethral valves
- Other anatomical variants
CT urography - if ultrasound is inconclusive or in adults with suspected stones or complex anatomy 2
History-Specific Risk Factors
Actively investigate these predisposing conditions:
- Recent urological instrumentation: catheterization, cystoscopy, ureteral stenting 2
- Indwelling devices: current or recent urinary catheters 6
- Immunocompromise: diabetes mellitus (present in both reported bacteremia cases), immunosuppressive therapy 1, 2
- Neurogenic bladder or incomplete voiding: detrusor dysfunction, overactive bladder 1
- Stone disease: nephrolithiasis is a key association 2
- Prior urological surgery or procedures
Laboratory Workup
Beyond urine culture:
- Blood cultures (two sets) if fever or systemic symptoms present - S. epidermidis can cause bacteremia from pyelonephritis 6, 2
- Complete blood count - assess for leukocytosis
- Metabolic panel - evaluate renal function, especially if obstruction suspected
- Repeat urine culture if initial diagnosis uncertain - multiple positive cultures strengthen the diagnosis of true infection versus contamination 5
Critical Clinical Pitfall
The most common error is dismissing S. epidermidis as a contaminant 3, 4, 7. While historically considered non-pathogenic in urine, multiple case reports demonstrate it causes genuine UTIs and even pyelonephritis with bacteremia. The key differentiator is the presence of symptoms plus identification of predisposing factors. Even in previously healthy children without obvious risk factors, S. epidermidis UTI warrants full anatomical evaluation, as occult abnormalities are frequently discovered 3, 4.
Treatment Considerations During Workup
While completing the workup:
- Initiate appropriate antimicrobial therapy based on culture sensitivities - do not delay treatment while awaiting imaging 3
- Address any obstruction immediately if identified - this is critical for source control 6
- Consider ureteral stenting if nephrolithiasis with obstruction is present 2
Special Population Considerations
In children: The threshold for comprehensive workup should be lower, as vesicoureteral reflux and congenital abnormalities are common underlying causes 4, 5, 7
In catheterized patients: Replace or remove the catheter before starting antimicrobial therapy 6