What Does Mixed Urogenital Flora Mean?
Mixed urogenital flora indicates specimen contamination during collection, typically from perineal, vaginal, or urethral skin bacteria, and should not be used to diagnose urinary tract infection or guide treatment. 1
Understanding the Term
The term "urogenital" specifically refers to voided urine samples that are contaminated with microbiota from the urethra, genitals, and skin during collection. 2 When a laboratory reports "mixed flora," this means multiple bacterial organisms (≥2 species) have been isolated from your urine specimen. 1
This finding represents contamination in the vast majority of cases, not a true infection. 2, 1
Why Contamination Occurs
The likelihood of contamination varies dramatically by collection method:
- Clean-catch midstream specimens: 7.8-27% contamination rate 3, 1
- Sterile bag collection (in children): 43.9-67.6% contamination rate 3, 1
- Diaper collection: 29-60.7% contamination rate 3, 1
Improper perineal cleansing increases contamination rates from 7.8% to 23.9%. 3 In a recent study, midstream urine samples had 7.4 times higher odds of contamination compared to catheterized specimens. 4
Clinical Significance
Isolation of multiple organisms is considered a negative urine culture by most experts. 2 Even when colony counts exceed 100,000 CFU/mL, mixed flora lacks diagnostic validity for urinary tract infection. 1
The presence of nonhemolytic streptococci (viridans group) alongside epithelial cells strongly suggests contamination from normal skin and mucosal flora. 3
What You Should Do Next
If You Have Symptoms (frequency, urgency, pain with urination):
Obtain a new urine specimen using proper collection technique. 1
- For women: Consider urethral catheterization to minimize contamination (≥50,000 CFU/mL of a single organism = significant). 1
- For men: Clean-catch midstream specimen is acceptable (≥100,000 CFU/mL of a single organism = significant). 1
If You Have No Symptoms:
No further testing or treatment is indicated in most populations. 1 Contaminated cultures should never be used to diagnose UTI or guide antimicrobial therapy. 1
Important exceptions requiring screening and treatment include:
- Pregnant women 1
- Patients before urologic procedures with anticipated mucosal bleeding 1
- Patients before transurethral prostate resection 1
Critical Pitfalls to Avoid
- Never treat based on mixed flora results, as this leads to unnecessary antibiotic exposure and promotes resistance. 3, 1
- Do not delay specimen processing: Urine held at room temperature >1 hour or refrigerated >4 hours can yield falsely elevated counts. 3, 1
- Never use bag-collected specimens in children to confirm UTI, as 85% are false positives. 3, 1
Special Circumstances
While mixed flora typically represents contamination, there are rare exceptions in specific clinical settings. In patients with long-term urinary catheters, polymicrobial bacteriuria can occasionally represent true mixed infection. 5 However, this determination requires careful clinical correlation and should not be assumed from a single contaminated specimen. 6, 5