Bacteriuria, Asymptomatic

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Asymptomatic bacteriuria (ASB) is specific bacterial growth ≥105 CFU/mL in one and two consecutive midstream urine samples for men and women, respectively >18 years. This definition applies to individuals with no clinical symptoms (1).


  • Premenopausal females: 1–5%
  • Pregnancy: 2–10%
  • Older females and males: 4–19%
  • Institutionalized older population: 15–50%

  • Variable, increased with age, female gender, sexual activity, and presence of genitourinary (GU) abnormalities
  • Pregnancy: 2–10%
  • Short- and long-term indwelling catheter 9–23% and 100%, respectively
  • Long-term care residents in women 25–50% and men 15–40%

Etiology and Pathophysiology

  • Microbiology is similar to that of other UTI, with bacteria originating from periurethral area, vagina, or gut.
  • Organisms are less virulent in ASB than those causing UTI.
  • The most common organism is Escherichia coli. Other common organisms are Klebsiella pneumoniae, Enterobacter, Proteus mirabilis, Staphylococcus aureus, group B Streptococcus (GBS), and Enterococcus.

Genetic variations that reduce toll-like receptor-4 function (TLR4) have been associated with ASB by lowering innate immune response and delaying bacterial clearance.

Risk Factors

  • Pregnancy
  • Older age
  • Female gender
  • Sexual activity, use of diaphragm with spermicide
  • GU abnormalities: neurogenic bladder, urinary retention, urinary catheter use (indwelling, intermittent, or condom catheter)
  • Institutionalized elderly population
  • Diabetes mellitus
  • Immunocompromised status
  • Spinal cord injuries or functional impairment
  • Hemodialysis

Commonly Associated Conditions

Depends on the risk factors

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