What is it called when a patient has a Urinary Tract Infection (UTI) and subsequent blood cultures are positive, indicating bacteremia?

Urosepsis: Definition, Diagnosis, and Management

When a patient has a urinary tract infection (UTI) and subsequent positive blood cultures, this is called urosepsis or bacteremic urinary tract infection (bUTI). This condition represents a serious progression of a UTI where bacteria from the urinary tract enter the bloodstream, causing systemic infection.

Definition and Terminology

• Urosepsis: A systemic inflammatory response syndrome (SIRS) caused by a urinary tract infection that has spread to the bloodstream
• Bacteremic UTI (bUTI): The presence of bacteremia (bacteria in the bloodstream) originating from a urinary tract infection
• UTI bacteremia: Another term used to describe the same condition

Epidemiology and Significance

• Bacteremia complicates approximately 29-32% of hospitalized patients with complicated UTIs 1, 2
• The condition is associated with higher mortality rates compared to non-bacteremic UTIs 3
• In population-based studies, the age-adjusted incidence rate of bacteremic gram-negative UTI is approximately 55.3 per 100,000 person-years in females and 44.6 per 100,000 person-years in males 4

Risk Factors for Developing Bacteremia from UTI

Several factors increase the risk of a UTI progressing to bacteremia:

• Patient-related factors:

  • Chronic liver disease (highest risk factor - RR 18.978) 2
  • Impaired renal function/elevated serum creatinine 2, 3
  • Solid organ malignancy (OR 3.19) 5
  • Low body mass index (<18 kg/m²) 3
  • Community-acquired infection 3
  • Already receiving antibiotics at the time of hospitalization 1

• Clinical presentation factors:

  • Hydronephrosis 3
  • Band neutrophils >10% of WBC count 3
  • Hyperthermia or hypothermia 3
  • Elevated neutrophil count (>80% of neutrophils) (OR 5.84) 5
  • Elevated C-reactive protein (>100mg/L) 3, 5
  • Pyuria (≥50 white cells per high-power field) (OR 4.43) 5

• Microbiological factors:

  • Klebsiella species infections (more likely to cause bacteremia than other uropathogens) 2
  • E. coli remains the most common causative organism overall (74.9%) 4

Diagnostic Approach

When evaluating a patient with suspected urosepsis:

1. Obtain both urine and blood cultures before starting antibiotics

   • In 7% of patients, blood cultures may identify uropathogens not isolated from urine, especially in patients already on antibiotics 1

2. Laboratory tests:

   • Complete blood count with differential (looking for elevated neutrophil count)
   • C-reactive protein (values >100mg/L suggest higher bacteremia risk)
   • Serum creatinine
   • Urinalysis (looking for pyuria)

3. Imaging:

   • Consider imaging to identify structural abnormalities like hydronephrosis that increase bacteremia risk 3

Management

1. Empiric antimicrobial therapy:

   • For patients with systemic symptoms suggesting urosepsis, start with:

     • Amoxicillin plus an aminoglycoside, OR
     • A second-generation cephalosporin plus an aminoglycoside, OR
     • An intravenous third-generation cephalosporin 6

   • Ceftriaxone is an appropriate choice for bacteremic UTI as it covers most common uropathogens 7

2. Duration of therapy:

   • Treatment for 7-14 days is generally recommended for complicated UTIs 6
   • Duration should be tailored based on clinical response and the specific pathogen identified

3. Targeted therapy:

   • Adjust antibiotics based on culture and susceptibility results
   • Consider increasing antimicrobial resistance trends when selecting definitive therapy 4

Prognosis and Complications

• Bacteremic UTIs have higher mortality rates than non-bacteremic UTIs 3
• Independent risk factors for mortality include:
  • Bacteremic UTI itself (compared to non-bacteremic UTI)
  • Shock
  • Low body mass index (<18 kg/m²) 3

Important Clinical Considerations

• Don't delay treatment: In critically ill patients with suspected urosepsis, blood cultures can be drawn simultaneously (no need for intervals between sets) before promptly starting antibiotics 6

• Antibiotic resistance: Increasing resistance rates to common antibiotics (trimethoprim-sulfamethoxazole and ciprofloxacin) have been observed among gram-negative uropathogens 4, necessitating careful antibiotic selection

• Catheter-associated infections: For patients with indwelling catheters, obtain urine by aspiration of the catheter port, not from the drainage bag 6

• Structural abnormalities: Address any underlying urological abnormalities or obstructions that may be contributing to the infection 6

By recognizing the risk factors for bacteremic UTI and promptly initiating appropriate antimicrobial therapy, clinicians can improve outcomes for patients with this serious condition.