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Bacteriuria is defined as the presence of bacteria in uncontaminated urine. Bacteriuria can be associated with a symptomatic urinary tract infection or can simply reflect asymptomatic colonization. In the latter case, the significance and management depends on the patient population.

The presence of bacteria in urine can be established based on positive nitrite dipstick or culture. A clinically relevant degree of bacteriuria is defined as the growth of more than 105 colony forming units (CFUs) of bacteria per milliliter on urine culture. The presence of white blood cells in the urine, as indicated by either positive leukocyte esterase on dipstick or direct visualization on microscopy, suggests infection rather than mere colonization.
The prevalence of asymptomatic bacteriuria among young, nonpregnant women is 1% to 3%. The prevalence is higher among pregnant women, elderly patients, residents of long-term care facilities, and patients with conditions requiring frequent self-catheterization or chronic indwelling urinary catheters. Bacteriuria is much less common in men (< 0.1%) but increases with age, likely because of prostatic disease and consequent urinary retention.


The appropriate management of asymptomatic bacteriuria depends on patient characteristics.
In young children, asymptomatic bacteriuria in the setting of vesicoureteral reflux can lead to renal scarring and even failure. Thus patients with known reflux (see Plate 2-21) are often maintained on antibiotic prophylaxis until the reflux spontaneously improves or a definitive surgical intervention is performed. In healthy children without known reflux, general screening for or treatment of bacteriuria is not recommended.
In pregnant women, asymptomatic bacteriuria increases the risk of pyelonephritis, likely because of relaxation of smooth muscle around the ureters. As such, treatment of asymptomatic bacteriuria has been shown to decrease the likelihood of pyelonephritis from 20%-35% to less than 4%. Moreover, treatment lowers the probability of preterm labor and low birth weight. The current recommendation is to screen pregnant women by performing a urine culture around week 16 of gestation. The optimal frequency of screening is not known. If necessary, antimicrobial therapy should be instituted for 3 to 7 days.
In patients scheduled to undergo endourologic procedures that may injure the urinary mucosal, screening and treatment of bacteriuria is recommended. If necessary, treatment should begin just before the procedure. Treatment does not need to continue postoperatively unless a catheter is to remain in place.
In nonpregnant women, asymptomatic bacteriuria increases the risk of cystitis, but neither general screening nor treatment is recommended because bacteriuria tends to rapidly recur. Likewise, there is no benefit to general screening or treatment of asymptomatic bacteriuria in men. In diabetic patients, treating asymptomatic bacteriuria has not been shown to decrease or delay future urinary tract infections.
Similarly, in elderly individuals residing in long-term care facilities, the treatment of asymptomatic bacteriuria has failed to show benefits. In patients with chronic indwelling catheters, research comparing treatment with a placebo has shown no difference in infection rates and demonstrated higher rates of antibiotic resistance among patients receiving treatment.