Practice Essentials
Asymptomatic bacteriuria is defined as the presence of one or more species of bacteria growing in the urine at specified quantitative counts (≥105 colony-forming units [CFU]/mL or ≥108 CFU/L), irrespective of the presence of pyuria, in the absence of signs or symptoms attributable to urinary tract infection (UTI).
Asymptomatic bacteriuria (ABU) is common. The frequency varies among different populations, depending on factors such as age, sex, and underlying disorders (eg, diabetes mellitus or spinal cord injury). One study in hospitalized patients identified obesity and iron deficiency anemia as independent risk factors for ABU.
The frequency of ABU in different adult populations is as follows
:
Premenopausal women, 1-5%
Pregnant women, 1.5-9.5%
Women aged 50-70 years, 2.8-8.6%
Women aged 70 years or older in the community, 10.8 -16%
Men aged 70 years or older in the community, 3.6-19%
Women aged 70 years or older in a long-term care facility, 25-50%
Men aged 70 years or older in a long-term care facility, 15-50%
Women with diabetes, 10.8-16%
Men with diabetes, 0.7-11%
Individuals with spinal cord injury and intermittent cathetar use, 23-69%
Individuals with spinal cord injury and sphincterotomy/condom catheter, 57%
Individuals with long-term catheter use, 100%
Patient characteristics also influence the microbiology of ABU. Escherichia coli is the most common organism and is the most likely to occur in healthy persons. A variety of organisms may be found, however, including Enterobacteriaceae, Pseudomonas aeruginosa, Enterococcus species, and group B Streptococcus. In men, Enterococcus species and gram-negative bacilli are common. Catheterized nursing home residents may have polymicrobial ABU.
Laboratory criteria for the diagnosis of ABU in a midstream clean-catch urine specimen in patients without indwelling catheters are as follows
:
For women, 2 consecutive specimens with isolation of at least 100,000 colony-forming units (cfu) per mL of the same bacterial species
For men, a single specimen with isolation of at least 100,000 cfu/mL of a single bacterial species
For the diagnosis of ABU in a catheterized urine specimen of both men and women, organisms present in lower quantitative counts likely represent contamination of the urine specimen from organisms present in the biofilm along the device rather than true bacteriuria and, in these patients, ≥105 CFU/mL remains the most appropriate diagnostic criteria for bladder bacteriuria. Lower quantitative counts (≥102 to < 105 CFU/mL) isolated from urine specimens collected by “in and out” catheterization or following insertion of a new indwelling catheter suggest true bacteriuria, but the clinical significance of these lower quantitative counts in people without symptoms has not been evaluated.
In most patient populations, treatment of ABU is not clinically beneficial, and consequently, screening for ABU is not recommended.
The US Preventive Services Task Force advises against screening men and nonpregnant women for asymptomatic bacteriuria; there is adequate evidence to suggest that screening is ineffective in improving clinical outcomes. An important exception is pregnant women, for whom ABU carries significant risks and treatment provides important benefits.
Antibiotic treatment may also be valuable for children aged 5-6 years and before invasive genitourinary procedures.
However, the consensus is that catheterization has no clinical significance and that antibiotic prescription is not indicated in any of the following:
Elderly ABU patients
Healthy school girls and young women
Diabetic women
Patients who have indwelling catheters or undergo intermittent urinary catheterization
A study by Lin et al suggests the need for greater focus on optimizing the use of antibiotics in patients with enterococcal bacteriuria; overtreatment of ABU is common, especially in patients with pyuria.