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Multiple rod-shaped bacteria shown between the larger white blood cells at urinary microscopy from a patient with urinary tract infection.
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]

To view a comprehensive algorithm of common findings of urine composition and urine output, click here


In medicine, bacteriuria denotes the presence of bacteria in urine not due to contamination from urine sample collection.

Urine is normally a sterile bodily fluid when inside the bladder, but can pick up commensals and pathogens when exiting through the urethra. Bacteria in the urine, especially gram-negative rods, usually indicate a urinary tract infection (either cystitis or pyelonephritis), although bacteriuria can also occur in prostatitis. Escherichia coli is the most common bacterium isolated from urine samples.

Asymptomatic bacteriuria is bacteriuria without accompanying symptoms of a urinary tract infection (such as frequent urination, painful urination or fever). It is more common in women, in the elderly, in residents of long-term care facilities, and in patients with diabetes, bladder catheters and spinal cord injuries. Patients with a long-term Foley catheter uniformly show bacteriuria.

Prevalences of asymptomatic bacteriuria[1]
Group Prevalence (in %)
Healthy premenopausal women 1.0 to 5.0
Pregnant women 1.9 to 9.5
Postmenopausal women (50 to 70 years of age) 2.8 to 8.6
Patients with diabetes mellitus Women 9.0 to 27.0
Men 0.7 to 1.0
Older community-dwelling patients Women (older than
70 years)
> 15.0
Men 3.6 to 19.0
Older long-term care residents Women 25.0 to 50.0
Men 15.0 to 40.0
Patients with spinal cord injury Intermittent catheter 23.0 to 89.0
Sphincterotomy and
condom catheter
Patients undergoing hemodialysis 28.0
Patients with an indwelling catheter Short-term 9.0 to 23.0
Long-term 100


Bacteria can be detected with a urine dipstick test for urinary nitrite or by urinary microscopy, although bacterial culture remains the most specific and formal test (the golden standard). Bacteriuria can be confirmed if a single bacterial species is isolated in a concentration greater than 100,000 colony forming units per millilitre of urine in clean-catch midstream urine specimens (one for men, two consecutive specimens with the same bacterium for women). For urine collected via bladder catheterisation, the threshold is 100 colony forming units of a single species per millilitre. The threshold is also 100 colony forming units of a single species per millilitre for women displaying UTI symptoms.[2]


The presence of simultaneous pyuria does not warrant treatment by itself.

  • Screening for asymptomatic bacteriuria with urine culture and treatment with antibiotics is recommended during pregnancy, because it significantly reduces symptomatic urinary tract infections, low birth weight, and preterm delivery.[3][4]
  • Kidney transplant recipients, children with vesicoureteral reflux or others with structural abnormalities of the urinary tract, people with infected kidney stones and those who are having urological procedures might be more likely to benefit from treatment with antibiotics for asymptomatic bacteriuria.[6]

See also


  1. [1] PMID 17002033 (PMID 17002033)
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  2. Sam, Amir H. (2010). Rapid Medicine. Wiley-Blackwell. ISBN 1-4051-8323-3. Unknown parameter |coauthors= ignored (help)
  3. Lin K, Fajardo K (2008). "Screening for asymptomatic bacteriuria in adults: evidence for the U.S. Preventive Services Task Force reaffirmation recommendation statement". Ann. Intern. Med. 149 (1): W20–4. PMID 18591632. Unknown parameter |month= ignored (help)
  4. Smaill F, Vazquez JC. Antibiotics for asymptomatic bacteriuria in pregnancy. Cochrane Database Syst Rev. 2007;(2):CD000490. PMID 17443502
  5. Colgan R, Nicolle LE, McGlone A, Hooton TM. Asymptomatic bacteriuria in adults. Am Fam Physician. 2006;74(6):985-90. PMID 17002033
  6. Asymptomatic bacteriuria from Medline Plus. Updated May 26, 2006, retrieved January 28, 2008.

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