Staphylococcus saprophyticus in Urine: Clinical Significance
S. saprophyticus in urine indicates a urinary tract infection, particularly in young, sexually active women, and is the second most common cause of acute UTI in this population after E. coli. 1
What This Finding Means
S. saprophyticus is a true uropathogen, not a contaminant, unlike most other coagulase-negative staphylococci (such as S. epidermidis) which typically represent contamination when found in urine 2, 1
This organism accounts for 10-20% of acute UTIs in young women (15-30 years of age), making it the second most frequent causative agent after E. coli 1
The bacterium is less common in children, men, and elderly patients, though it can occur in these populations 2
Clinical Presentation
Patients typically present with symptomatic cystitis including dysuria, frequency, urgency, and suprapubic pain 1
Signs of upper tract involvement (flank pain, fever) are also frequently present, even though this is often classified as uncomplicated cystitis 2, 1
The urine sediment characteristically shows significant pyuria (leukocytes) on microscopy 1
Diagnostic Thresholds
Colony counts ≥50,000 CFU/mL of S. saprophyticus as a single organism in symptomatic patients represent significant infection requiring treatment 3
Lower colony counts (even <100,000 CFU/mL) can still indicate true infection when S. saprophyticus is isolated, particularly in symptomatic patients, as this organism often presents with lower bacterial counts than E. coli 1
The presence of a single organism rather than mixed flora strongly supports true infection rather than contamination 4
Treatment Approach
First-line treatment options include nitrofurantoin or amoxicillin-clavulanate for 7-10 days based on susceptibility testing 4
S. saprophyticus is usually susceptible to most antibiotics commonly used for UTI, with the notable exception of nalidixic acid 1
Ciprofloxacin is effective against S. saprophyticus according to FDA labeling, though fluoroquinolones should not be first-line due to resistance concerns with other organisms 5
Treatment duration should be 7-10 days for uncomplicated UTI 3, 4
Important Clinical Caveats
Do not dismiss this as contamination - this is a critical pitfall. Many clinicians mistakenly disregard coagulase-negative staphylococci in urine, but S. saprophyticus is a genuine pathogen 2, 1
Chemical screening tests (dipstick) may not always detect S. saprophyticus UTI, as the organism may not produce nitrites reliably 1
The bacterium shows seasonal variation with peak incidence in late summer and early fall, and has a zoonotic origin from cattle and pigs 6
Novobiocin resistance is traditionally used to identify S. saprophyticus in the laboratory, but this test alone may select a heterogeneous group of coagulase-negative staphylococci and is not 100% reliable 7
When to Treat
Treat all symptomatic patients with S. saprophyticus meeting diagnostic thresholds (≥50,000 CFU/mL) 3, 4
Do not treat asymptomatic bacteriuria except in pregnant women or patients undergoing urological procedures with anticipated mucosal bleeding 8
Clinical improvement should occur within 48-72 hours of appropriate therapy; if symptoms persist beyond 72 hours, repeat urinalysis should be considered 4