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Asymptomatic bacteriuria (ASB)

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Asymptomatic bacteriuria is the presence of bacteria in the urine despite the patients being withour any symptoms (1). It is a common finding in the elderly population and is not associated with increased morbidity and mortality (2)

  • asymptomatic bacteriuria (ASB) develops when bacteria colonising the gut, vagina, or perineum ascend upwards from the urinary meatus into the urethra, bladder and in some cases, the ureters, and kidneys

  • ASB is defined as the presence of bacteria at a threshold of>=10 ^5 colony-forming units (CFUs) per millilitre (ml) or>=10^8 CFU per litre in the urine without symptoms of urinary tract infection (UTI)

  • ASB is a normal physiological state in some people with increasing prevalence with age (2)

  • the definition of ASB was restated in 2019 by the Infectious Diseases Society of America (IDSA) as being>=10^5 CFU per ml or>=10^8 CFU per litre of a voided urine sample in people without indwelling catheters or signs or symptoms of UTI
    • IDSA recommended that in women, two consecutive samples should be collected within a two-week interval in order to confirm the presence of ASB, noting that between 10% and 60% of women (varying with population characteristics) have confirmed ASB on repeat testing following a first positive result (3)
    • the Scottish Intercollegiate Guidelines Network (SIGN) also recommends that ASB should be confirmed with a second urine culture (7) however, this is not current practice in England

Most common organism causing asymptomatic bacteriuria is Escherichia coli with Enterobacteriacea; Pseudomonas aeruginosa, Enterococcus species, and group B streptococcus making up the other organisms.

Screening and treatment of asymptomatic bacteriuria should be done in:

  • pregnant women
  • people undergoing traumatic genitourinary procedures (4)

Asymptomatic bacteriuria may be a finding on urine microscopy, culture and sensitivity.

  • if this condition occurs during pregnancy then it should be treated - during pregnancy asymptomatic bacteriuria is associated with premature delivery and low birthweight
  • in a non-pregnant woman with a normal urinary tract, no treatment is required - occurs in 15-20% of women aged 65-70 years and does not seem to impair renal function or shorten life (5)
    • the relationship between bacteriuria and UTI symptoms is unclear and asymptomatic bacteriuria in young, healthy and non-pregnant women is not associated with renal damage (6)
    • there is evidence that asymptomatic bacteriuria or pyuria in the elderly does not need to be investigated or treated, as treatment does not improve outcome (7)
    • in males chronic prostatitis may result in asymptomatic bacteruria

In the following groups of patients either screening or treatment of asymptomatic bacteriuria is not recommended:

  • pre menopausal, non pregnant women
  • diabetic women
  • older persons living in the community
  • elderly institutionalized patients
  • persons with spinal cord injury
  • catheterized patients while the catheter remains in situ (3).

Antibiotics are not given for non pregnant women and elderly women (over 65 years of age) with asymptomatic bacteriuria (6). Antibiotics should be given to patients before an invasive urogenital procedure (3).

Antibiotics versus no treatment for asymptomatic bacteriuria in aged care residents (7):

  • a systematic review and meta-analysis found antibiotic therapy was associated with an increased chance of bacteriological cure (vs placebo/no treatment (RR 1.89; 95%CI 1.08-3.32) but a higher rate of adverse effects (5.62; 1.07-29.55)
  • study authors suggest harms may outweigh benefits


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