Should a patient with a urine culture of 100,000 CFU/mL Citrobacter koseri and urinalysis showing occult blood and red blood cells, but no urinary symptoms, be treated?

Does a Patient with 100,000 CFU/mL Citrobacter koseri and Occult Blood/RBCs but No Urinary Symptoms Need Treatment?

No, this patient should not be treated with antibiotics. This represents asymptomatic bacteriuria (ASB), which should not be treated except in pregnant women or patients undergoing urologic procedures with anticipated mucosal bleeding. 1, 2

Diagnostic Criteria for Urinary Tract Infection

Both pyuria AND acute urinary symptoms are required to diagnose and treat a UTI. 1, 2

Required Components:

• Pyuria: ≥10 WBCs/high-power field OR positive leukocyte esterase 1, 2
• Acute urinary symptoms: dysuria, frequency, urgency, fever >38.3°C, or gross hematuria 1, 2

Occult blood and RBCs alone do NOT constitute urinary symptoms and do not justify treatment. 2 Microscopic hematuria requires ≥3 RBCs/HPF on repeat testing to be clinically significant, and even then does not indicate infection without accompanying pyuria and symptoms. 2

Why Asymptomatic Bacteriuria Should Not Be Treated

The Infectious Diseases Society of America issues a Grade A-II strong recommendation against treating asymptomatic bacteriuria. 1, 2

Evidence Against Treatment:

• Provides no clinical benefit: Does not prevent symptomatic UTI, renal injury, or progression of kidney disease 1, 2
• Increases antimicrobial resistance and promotes reinfection with more resistant organisms 1, 2
• Causes harm: Increases risk of Clostridioides difficile infection and exposes patients to unnecessary drug toxicity 2
• High prevalence: ASB occurs in 15–50% of elderly individuals and long-term care residents 1, 2

Colony Count Interpretation

100,000 CFU/mL meets the traditional threshold for significant bacteriuria (≥10⁵ CFU/mL), but this threshold was established to distinguish infection from contamination—not to determine who needs treatment. 1, 3

• In symptomatic patients with pyuria, even lower counts (10,000–50,000 CFU/mL) can represent true infection 4, 5, 6
• In asymptomatic patients, even high colony counts should not trigger treatment 1, 2

The diagnosis of UTI requires both quantitative culture results AND evidence of pyuria/symptoms together, not culture alone. 3

Citrobacter koseri Considerations

Citrobacter koseri is an opportunistic pathogen that commonly causes urinary tract infections in adults. 7 More than half of C. koseri isolates in one series originated from urinary tract infections. 7 However, the organism's pathogenic potential does not change the requirement for symptoms and pyuria before initiating treatment. 1, 2

Exceptions Where ASB Treatment IS Indicated

Only two clinical scenarios warrant treatment of asymptomatic bacteriuria: 1, 2

1. Pregnant women (screen in first trimester to prevent pyelonephritis, preterm delivery, and low birth-weight infants) 1, 2
2. Patients undergoing urologic procedures with anticipated mucosal bleeding (e.g., transurethral resection of prostate) 1, 2

Clinical Management Algorithm

If Patient Has NO Urinary Symptoms:

• Do not order urinalysis or culture in asymptomatic individuals 2
• Do not prescribe antibiotics 1, 2
• Educate patient to return if specific urinary symptoms develop (dysuria, fever, frequency, urgency, suprapubic pain, gross hematuria) 2

If Patient Develops Urinary Symptoms:

• Obtain properly collected urine specimen for urinalysis 1, 2
• Confirm pyuria (≥10 WBC/HPF or positive leukocyte esterase) 1, 2
• Obtain urine culture before starting antibiotics 2
• Initiate empiric therapy: Nitrofurantoin 100 mg orally twice daily for 5–7 days (first-line for uncomplicated cystitis) 2

Common Pitfalls to Avoid

• Never treat based on culture results alone without confirming both urinary symptoms and pyuria 1, 2
• Do not interpret occult blood or microscopic hematuria as a urinary symptom—these findings do not indicate infection 2
• Pyuria alone (without symptoms) has exceedingly low positive predictive value (≈43–56%) and should not trigger treatment 2
• Non-specific symptoms in elderly patients (confusion, falls, functional decline) do not justify UTI treatment without specific urinary symptoms 1, 2
• Colony count alone should not dictate treatment—clinical context (symptoms, pyuria) is essential 2

Quality of Life and Antimicrobial Stewardship

Unnecessary antibiotic treatment causes harm without providing benefit: 2

• Increases antimicrobial resistance
• Exposes patients to adverse drug effects
• Increases healthcare costs
• Promotes colonization with more resistant organisms

Educational interventions on diagnostic protocols provide a 33% absolute risk reduction in inappropriate antimicrobial initiation. 2