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Is antibiotic treatment indicated in a patient with a positive urine culture but no symptoms?

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The 2005 Infectious Diseases Society of America (IDSA) guidelines1 recommend screening pregnant women and patients who will undergo an invasive urologic procedure with a urine culture and treating them with antibiotics if bacteriuria is significant. The IDSA recommends against screening for or treating asymptomatic bacteriuria in other populations.


A positive urine culture can represent three different conditions:

  • Symptomatic urinary tract infection
  • Contamination of the sample by organisms that are present distal to the bladder and that enter the urine at the time the specimen is collected
  • Asymptomatic bacteriuria, defined as the isolation of a specified quantitative count of a single uropathogen in an appropriately collected urine specimen obtained from someone without symptoms or signs attributable to a urinary tract infection (Table 1). It represents the true presence of bacteria in the bladder and may be thought of as a state of colonization.


Rates vary depending on the age (higher in older persons), sex (higher in women), and presence of genitourinary abnormalities of the population studied. Prevalence rates are estimated to be 1% to 5% in healthy premenopausal women, 2% to 9% in pregnant women, 9% to 27% in diabetic women, 15% to 50% in elderly men and women in long-term care facilities, and 28% in patients undergoing hemodialysis.2–6 In patients with an indwelling urinary catheter, the rate goes up by 3% to 8% per day, and bacteriuria is nearly universal at 30 days.7,8 Asymptomatic bacteriuria can be transient, as commonly occurs in healthy young women, or it may be more prolonged, as commonly occurs in elderly patients or those with a chronic indwelling urinary catheter.


Screening for asymptomatic bacteriuria and treating it are strongly recommended (grade A-I recommendation) in pregnant women and in men who will undergo transurethral resection of the prostate.

Pregnant women have a risk of pyelonephritis 20 to 30 times higher if they have asymptomatic bacteriuria.9 Cohort studies and randomized clinical trials have consistently reported significant reductions in rates of pyelonephritis and low birth weight when antibiotic therapy is given for asymptomatic bacteriuria during pregnancy.

The ideal time to screen for this in pregnancy is between the 9th and 16th weeks of gestation. The appropriate screening test is a urine culture, since screening for pyuria has a low sensitivity and specificity. The choice of antibiotic is based on the results of culture. Antibiotics that have been safely used in these patients include nitrofurantoin, cephalexin, amoxicillin, and fosfomycin.10 The recommended treatment duration is between 3 and 7 days. Periodic screening for recurrent bacteriuria should be performed during the remainder of the pregnancy.

Men about to undergo transurethral resection of the prostate1 who have asymptomatic bacteriuria before the procedure have a 60% rate of bacteremia and a 6% to 10% rate of sepsis after the procedure if they do not receive antibiotic therapy. Clinical trials have documented significant reductions in these complications when antimicrobial therapy is given before the procedure.

Screen for and treat asymptomatic bacteriuria in pregnant women and patients undergoing invasive urologic procedures

The optimal time for obtaining the urine culture, the optimal time for starting antimicrobial therapy, and the optimal duration of antimicrobial therapy are not well defined, although some data support giving antibiotics the night before or just before the procedure.

The recommendation has been extrapolated to include not only men undergoing transurethral resection of the prostate but also any patient undergoing a urologic procedure associated with significant mucosal bleeding.

Women with catheter-acquired asymptomatic bacteriuria. If the bacteriuria persists 48 hours after catheter removal, the IDSA guidelines state that antibiotic therapy may be considered (grade B-I recommendation). However, there are no recommendations to screen women 48 hours after catheter removal.

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