MPA | Pharmacy News

Asymptomatic Bacteriuria

Posted on May 15, 2018 in: Patient Safety

By Jennifer Chou, PharmD, PGY2 infectious diseases pharmacy resident, Beaumont Hospital, Royal Oak


Overtreatment of asymptomatic bacteriuria (ASB) remains a common problem that can lead to increased antibiotic resistance, increased risk for C. difficile infection and adverse effects. ASB is the isolation of bacteria in a urine culture from a patient without symptoms such as dysuria, urinary frequency, urgency or suprapubic pain. According to the Infectious Diseases Society of America (IDSA) guidelines for asymptomatic bacteriuria, bacteriuria in women is defined as having two consecutive samples with the same isolate at quantities ≥ 105 CFU/mL.1 The definition in men is one sample with quantities ≥ 105 CFU/mL, and in catheterized patients, a cutoff of ≥ 102 CFU/mL is used for both men and women.1 However, there are a variety of definitions used in the literature. The prevalence of ASB in healthy, premenopausal women is one to five percent, in contrast to rates closer to 20 percent among those aged ≥ 70 years in the community. Rates are as high as 50 percent among elderly in long-term care facilities, and 100 percent among those with long-term indwelling catheters.1 The IDSA guidelines recommend treatment of ASB only in pregnant women, before transurethral resection of the prostate or before urologic procedures in which mucosal bleeding is expected.

Over treatment of ASB stems from the difficulty in assessing for true ASB versus urinary tract infection (UTI). The populations with the highest prevalence of ASB can also be the most difficult to assess for symptoms. Elderly patients frequently present with altered mental status as the only potential symptom or have an inability to report symptoms due to baseline cognitive impairment. While altered mental status can be a symptom of UTI in the elderly, it is important to assess for other potential culprits, such as new and/or recent medications (opioids, benzodiazepines, etc.). It is also important to note that an elderly patient presenting to the hospital after a fall is not an automatic indication to order a urine culture. In these gray-area cases when altered mental status is the only potential symptom, the decision to treat is on a case-by-case basis, relying on a thorough history and evaluation of alternative explanations.

In a meta-analysis including 30 studies, the rate of inappropriate ASB treatment was 45 percent in North America.2 Factors associated with a higher likelihood of treatment were patients with gram-negative isolates, female gender, pyuria and nitrite positivity.2 Overtreatment of ASB is often due to a reflexive action to order a urinalysis and/or urine culture, with subsequent reaction to treat a positive culture. One potential area for intervention is preventing the ordering of the initial culture. One study group at Veterans Affairs healthcare systems developed a catheter-associated urinary tract infection (CAUTI) diagnostic algorithm with audit and feedback at two decision points: ordering of urine culture and treating a positive urine culture.3 With this intervention, rates of urine culture ordering decreased significantly from 41 to 23 per 1000 bed-days. Overtreatment of ASB also decreased significantly, without affecting under treatment of CAUTI. These decreases were sustained during the one-year maintenance period.3 However, old habits may die hard, and another study evaluated a different approach for non-catheterized patients at an acute care hospital in Toronto. Rather than reporting positive urine culture results in non-catheterized patients, the following message was posted instead: “The majority of positive urine cultures from inpatients without an indwelling urinary catheter represent asymptomatic bacteriuria. If you strongly suspect that your patient has developed a urinary tract infection, please call the microbiology laboratory.”4 Of the positive urine cultures over a period of two months, UTI was present in only two percent of patients. The ASB treatment rate dropped from 48 percent to 12 percent and calls were only made on five of 37 patients. No clinical signs of UTI or sepsis were identified in those untreated.4 Stewardship interventions should be tailored based on site-specific preferences and practices in order to be most effective. In another meta-analysis of 50 studies, there was no apparent benefit with ASB treatment among patients with no risk factors, diabetes, postmenopausal women, elderly institutionalized patients and renal transplant patients.5


Overtreatment of ASB remains prevalent and has been a recent focus of antimicrobial stewardship initiatives. Provider education and a multi-pronged stewardship approach is likely necessary and will be most effective in reducing overtreatment of ASB.



1.      Nicolle LE, Bradley S, Colgan R, et al. Infectious Diseases Society of America Guideline for the diagnosis and treatment of asymptomatic bacteriuria in adults. Clin Infect Dis 2005;40:643–654.

2.      Flokas ME, Andreatos N, Alevizakos M, et al. Inappropriate management of asymptomatic patients with positive urine cultures: A systematic review and meta-analysis. Open Forum Infect Dis 2017;4(4).

3.      Trautner BW, Grigoryan L, Petersen NJ, et al. Effectiveness of an antimicrobial stewardship approach for urinary catheter-associated asymptomatic bacteriuria. JAMA Intern Med 2015;175:1120–7.

4.      Leis JA, Rebick GW, Daneman N, et al. Reducing antimicrobial therapy for asymptomatic bacteriuria among noncatheterized inpatients: a proof-of-concept study. Clin Infect Dis 2014;58(7):980-3.

5.      Köves B, Cai T, Veeratterapillay R, et al. Benefits and harms of treatment of asymptomatic bacteriuria: A systematic review and meta-analysis by the European Association of Urology Urological Infection Guidelines Panel. Eur Urol 2017;72(6):865-868.

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