> Table of Contents > Bacteriuria, Asymptomatic
Bacteriuria, Asymptomatic
Mony Fraer, MD, FACP, FASN
Kantima Phisitkul, MD
image BASICS
Asymptomatic bacteriuria (ASB) is diagnosed when significant bacteriuria is not accompanied by signs and symptoms attributable to urinary tract infection (UTI).
  • General population: 3.5%
  • Pregnancy: 7-10%
  • Older women: 16-18%
  • Variable, increased with age, female gender, sexual activity, and presence of genitourinary (GU) abnormalities
  • Pregnancy: 2-10%
  • Short- and long-term indwelling catheter 9-23% and 100%, respectively
  • Long-term care residents in women 25-50% and men 15-40%
  • Microbiology is similar to that of other UTI, with bacteria originating from periurethral area, vagina, or gut.
  • Organisms are less virulent in ASB than those causing UTI.
  • The most common organism is Escherichia coli. Other common organisms are Klebsiella pneumonia, Enterobacter, Proteus mirabilis, Staphylococcus aureus, group B Streptococcus (GBS), and Enterococcus.
Genetic variations that reduce toll-like receptor-4 function (TLR4) have been associated with ASB by lowering innate immune response and delaying bacterial clearance.
  • Older age
  • Female gender
  • Sexual activity, use of diaphragm with spermicide
  • GU abnormalities: neurogenic bladder, urinary retention, urinary catheter use (indwelling, intermittent, or condom catheter)
  • Institutionalized residents
  • Diabetes mellitus
  • Immunocompromised status
  • Spinal cord injuries or functional impairment
  • Hemodialysis
  • Pregnancy (decreased peristalsis of the urinary tract)
Depends on the risk factors
  • Afebrile
  • No suprapubic and costovertebral angle tenderness
  • UTI
  • Contaminated urine specimen
Initial Tests (lab, imaging)
  • Urinalysis (UA):
    • The presence of pyuria, leukocyte esterase, and nitrite in ASB is common.
  • Urine culture
  • Screening urine culture in asymptomatic patients is indicated in only two conditions:
    • Pregnancy: screening between 12 and 16 weeks' gestation or at first prenatal visit if later (1)[A]
    • Prior to transurethral resection of prostate (TURP) (1)[A] or any urologic interventions when mucosal bleeding is anticipated (1)[C].
  • Screening for ASB in men and nonpregnant women is not recommended.
Follow-Up Tests & Special Considerations
  • Noncontaminated urine specimen should be used for urine culture.
  • In pregnancy, periodic screening urine culture should be done after ASB treatment (1)[A] but not required in GBS bacteriuria (2,3)[C].
Test Interpretation
  • Patient with significant bacteriuria with or without pyuria and without symptoms referable to UTI should be diagnosed as ASB per Infectious Diseases Society of America.
    • Significant bacteriuria is defined based on type of urine specimen, sex, and the amount of bacteria.
    • By midstream, clean catch specimen
      • Male: >100,000 CFU/mL of single bacteria species
      • Female: the same criteria as male but needs two positive consecutive specimens
      • By catheterized specimen male and female: >100 CFU/mL of one bacterial species. Required one-time collection only
  • The presence of pyuria or leukocyte esterase is common but not a marker of infection.
  • Positive nitrite is an indicator of the presence of bacteriuria, but cannot differentiate UTI from ASB or poor collection technique.

  • Pregnancy
    • Intrapartum antibiotic prophylaxis with IV penicillin or clindamycin (penicillin allergy) is recommended for women with GBS bacteriuria occurring at any stage of pregnancy and of any colony count to prevent GBS disease in the newborn (2)[C].
    • No consensus on choice of antibiotics and duration of treatment in pregnancy; however, the cure rate is higher for the 4 to 7 days of treatment than one-day treatment (1)[A].
    • Choice of antibiotics should be guided by bacterial pathogen, local resistance rate, adverse effects, and comorbidities of patients (5).
    • Common oral antibiotics (FDA-B) that have been used
      • Nitrofurantoin 100 mg BID for 5 days (low level of resistance, may cause hemolysis in glucose-6-phosphate dehydrogenase deficiency)
      • Amoxicillin/clavulanate 500/125 BID for 5 to 7 days
      • Cefuroxime 250 mg BID for 5 days
      • Cephalexin 500 mg BID for 5 days
      • Fosfomycin 3 g for 1 single dose (not effective when glomerular filtration rate is less than 30 mL/min, may be used in highly resistant bacteria such as methicillin-resistant Staphylococcus aureus [MRSA], vancomycin-resistant enterococci [VRE], and extended-spectrum beta-lactamase [ESBL]-producing organism bacteria) (6)
    • Avoid trimethoprim in 1st trimester and near term. Avoid sulfa after 32 weeks' gestation.
    • Contraindicated: fluoroquinolones (FDA-C), tetracyclines (FDA-D)
  • Prior to invasive urologic interventions
    • Initiate antibiotic the night before or immediately before the procedure (1)[A].
    • Antibiotic should be continued until the indwelling catheter is removed postprocedure (1)[B].
No consensus on screening frequency of ASB in pregnancy, but monthly screening of urine culture after ASB treatment is recommended except GBS (1,2).
Patient Monitoring
Development of any signs/symptoms of UTI should warrant antibiotic treatment.
Daily cranberry juice may reduce the frequency of ASB during pregnancy, but it has not been confirmed in large study (see “Additional Reading”).
Patient should seek medical attention when UTI symptoms develop.
1. Nicolle LE, Bradley S, Colgan R, et al. Infectious Diseases Society of America guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults. Clin Infect Dis. 2005;40(5):643-654.
2. Zolotor AJ, Carlough MC. Update on prenatal care. Am Fam Physician. 2014;89(3):199-208.
3. Nicolle LE. Asymptomatic bacteriuria. Curr Opin Infect Dis. 2014;27(1):90-96.
4. Trautner BW, Grigoryan L. Approach to a positive urine culture in a patient without urinary symptoms. Infect Dis Clin North Am. 2014;28(1):15-31.
5. Mody L, Juthani-Mehta M. Urinary tract infections in older women: a clinical review. JAMA. 2014; 311(8):844-854.
6. Keating GM. Fosfomycin trometamol: a review of its use as a single-dose oral treatment for patients with acute lower urinary tract infections and pregnant women with asymptomatic bacteriuria. Drugs. 2013;73(17):1951-1966.
Additional Reading
  • Ragnarsdóttir B, Svanborg C. Susceptibility to acute pyelonephritis or asymptomatic bacteriuria: host-pathogen interaction in urinary tract infections. Pediatr Nephrol. 2012;27(11):2017-2029.
  • Wing DA, Rumney PJ, Preslicka CW, et al. Daily cranberry juice for the prevention of asymptomatic bacteriuria in pregnancy: a randomized, controlled pilot study. J Urol. 2008;180(4):1367-1372.
  • N39.0 Urinary tract infection, site not specified
  • B96.20 Unsp Escherichia coli as the cause of diseases classd elswhr
  • B96.1 Klebsiella pneumoniae as the cause of diseases classd elswhr
Clinical Pearls
  • ASB is a common and benign disorder for which treatment is not indicated in most patients.
  • The presence of pyuria, leukocyte esterase, and nitrite is common in ASB and not an indication for antimicrobial treatment.
  • Antibiotic treatment is indicated for ASB in pregnancy and patients who require urologic procedure in which mucosal bleeding is anticipated.
  • Treatment of ASB in other conditions does not decrease the frequency of UTI or improve outcome.
  • Overtreatment of ASB may result in negative consequences such as antimicrobial resistance, adverse drug reaction, and unnecessary cost.