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Asymptomatic bacteriuria

Background

Overview

Definition
ASB is defined as the presence of bacteria in an uncontamined urine sample at a microbial load of ≥ 10⁵ CFU/mL, without any associated signs or symptoms of UTI.
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Pathophysiology
ASB is most frequently caused by E. coli, followed by P. mirabilis, K. pneumoniae, Enterobacter species, P. aeruginosa, Enterococcus species, S. aureus, S. saprophyticus, and Streptococcus agalactiae.
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Epidemiology
The prevalence of ASB is 1-2% in healthy men, 1-9% in healthy women, 2-15% in pregnant women, 1-30% in diabetic adults, 2-50% in community-dwelling adults, 14-75% in institutionalized adults, and 9-100% in patients with indwelling catheters.
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Risk factors
Risk factors for ASB include female sex, advancing age, the use of indwelling catheters, pregnancy, diabetes mellitus, glucosuria, a history of UTIs, prostatic obstruction, neurological disorders, inadequate peri-anal hygiene, insufficient fluid intake, and overactive bladder syndrome.
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Disease course
In patients with ASB, symptoms of UTI are absent for a variety of reasons, including attenuated host immune response, as well as reduced microbial virulence, growth rates, and cell densities.
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Prognosis and risk of recurrence
Treatment of ASB should be avoided in low-risk populations given the absence of demonstrated benefit, potential for adverse drug reactions, and risk of promoting antibiotic-resistance. Select patients who may derive benefit from treatment include pregnant women and patients undergoing certain invasive procedures.
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Guidelines

Key sources

The following summarized guidelines for the evaluation and management of asymptomatic bacteriuria are prepared by our editorial team based on guidelines from the European Association of Urology (EAU 2025), the European Association of Urology (EAU/EAUN 2025), the American College of Obstetricians and Gynecologists (ACOG 2023), the American Urological Association (AUA/CUA/SUFU 2019), the Infectious Diseases Society of America (IDSA 2019,2016,2015,2010), the ...
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Screening and diagnosis

Indications for screening, pregnant patients: as per EAU 2025 guidelines, screen for and treat ASB in pregnant patients with standard short course treatment or single dose fosfomycin trometamol.
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  • Indications for screening (catheterized patients)

  • Indications for screening (patients undergoing urologic surgery)

  • Indications for screening (patients with a renal transplant)

  • Indications for screening (patients with nonrenal transplants)

  • Indications for screening (patients not to screen)

  • Diagnostic criteria (general population)

  • Diagnostic criteria (catheterized patients)

Diagnostic investigations

Urine tests
As per SEIMC 2017 guidelines:
Do not obtain urine test strips for the detection of ASB.
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Obtain an initial urine culture in pregnant females at 12-16th weeks of gestation.
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Medical management

Indications for antibiotics, pregnant patients: as per ACOG 2023 guidelines, administer targeted antibiotics for 5-7 days in pregnant patients with ASB with colony counts of ≥ 10⁵ CFU/mL.
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  • Indications for antibiotics (catheterized patients)

  • Indications for antibiotics (patients undergoing urologic procedures)

  • Indications for antibiotics (patients undergoing spinal surgery)

  • Indications for antibiotics (patients with a renal transplant)

  • Indications for antibiotics (patients with nonrenal transplants)

  • Indications for antibiotics (patients not to treat)

  • Duration of treatment

Specific circumstances

Pregnant patients: as per SOGC 2012 guidelines, treat any bacteriuria with colony counts ≥ 10⁵ CFU/mL in pregnancy.
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  • Elderly patients

  • Catheterized patients

  • Patients with asymptomatic candiduria

Preventative measures

Routine catheter change: as per IDSA 2010 guidelines, insufficient evidence to recommend routine catheter change (such as every 2-4 weeks) in patients with functional long-term indwelling urethral or suprapubic catheters to reduce the risk of catheter-associated ASB or catheter-associated UTI.
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Follow-up and surveillance

Post-treatment surveillance
As per SEIMC 2017 guidelines:
Obtain a follow-up urine culture to verify bacteriuria eradication in pregnant patients.
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Obtain subsequent monthly urine cultures until delivery.
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