Last updated on: April 13th, 2021

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Asymptomatic Bacteriuria

Clinicals - History


Asymptomatic bacteriuria (ABU) is the presence of ≥100,000 colony forming units (CFU) of bacteria per millilitre of urine, of the same pathogen, in a midstream/clean catch urine sample, with or without pyuria (on urinalysis), in the absence of urinary symptoms.

In women, 2 consecutive samples (collected within 2 weeks) meeting the above criteria of the same uropathogen, are required due to the common finding of transient bacteriuria in healthy young women. In men, one sample is sufficient to make the diagnosis.

In a patient with an indwelling catheter, a total bacteria count of more than or equal to 1,000 CFU organisms/ml in a single sample (also in the absence of urinary symptoms) is sufficient.

A count of 100 CFU organisms/ml is diagnostic of ABU in a patient whose urine sample is collected via temporary catheterization (an in and out catheter).

Risk Factors

ABU is common, although prevalence varies greatly when age, sex and genitourinary abnormalities are taken into consideration. This increases with age from ~1% in school-age girls to >20% in healthy women aged 80 and beyond.

Women who are sexually active, have diabetes mellitus (DM), or who are pregnant or post-menopausal have an increased risk of developing ABU. In particular, women with DM show a 8-14% prevalence higher than that in the general population. This difference is however not seen in men with DM.

In patients with long term indwelling catheters or permanent ureteric stents, prevalence is approximately 100%. Individuals with spinal cord injuries have a prevalence of more than 50%. Individuals with a history of recurrent urinary tract infections (UTI), congenital renal anomalies, the elderly and institutionalized also have a higher prevalence of ABU.

Note that ABU is rare in healthy young males, prevalence rises however after the age of 60 (6% at age 60 and about 15% after age 75).


The hallmark of ABU is its lack of symptoms. This could be explained by differences in the pathogen, host or both. A reduced virulence of the invading organisms and lower levels of neutrophil toll-like receptor 4 expression have been found in patients with ABU.


The current evidence as regards the complications of ABU is controversial, with different studies showing different outcomes with regards to mortality, morbidity, malignancy and urosepsis.

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