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Bacteriuria, Asymptomatic

Basics

  • ASB: bacterial growth ≥10^5 CFU/mL in urine without UTI symptoms.
  • Applies to adults >18 years, men need one positive sample, women need two consecutive positives.
  • Most common organism: Escherichia coli; others include Klebsiella, Enterobacter, Proteus, Staph aureus, GBS, Enterococcus.

Epidemiology

  • Incidence varies: premenopausal females 1-6%, pregnancy 2-10%, older adults 4-19%.
  • Institutionalized elderly women 25-50%, men 15-40%.
  • Prevalence increases with age, female gender, sexual activity, neurogenic bladder, catheter use, diabetes, immunocompromise.

Etiology & Pathophysiology

  • Bacteria ascend from urethra to bladder.
  • Organisms in ASB less virulent than symptomatic UTI.
  • Genetic variants reducing TLR4 function may predispose to ASB.

Risk Factors

  • Pregnancy
  • Older age
  • Female gender
  • Sexual activity, diaphragm with spermicide use
  • GU abnormalities (neurogenic bladder, retention, catheters)
  • Institutionalized elderly
  • Diabetes mellitus
  • Immunocompromised state
  • Spinal cord injury
  • Hemodialysis

Diagnosis

History & Physical Exam

  • Asymptomatic: no fever, dysuria, urgency, frequency, or hematuria.
  • Afebrile, no suprapubic or costovertebral tenderness.

Diagnostic Tests

  • Urinalysis: pyuria, leukocyte esterase, nitrites common but nonspecific.
  • Urine culture (clean catch) required for diagnosis.
  • Screening recommended only in:
  • Pregnant women (12-16 weeks gestation or first prenatal visit)
  • Prior to transurethral resection of the prostate (TURP) or urologic procedures with mucosal bleeding risk.
  • Not recommended for screening men or nonpregnant women.

Treatment

Indications for Treatment

  • Pregnancy: reduces risk of pyelonephritis, low birth weight, preterm delivery.
  • Prior to TURP or invasive urologic procedures.

Medications in Pregnancy

  • Intrapartum IV penicillin or clindamycin (if penicillin allergic) for GBS bacteriuria.
  • Common oral antibiotics (FDA category B):
  • Nitrofurantoin 100 mg BID for 5 days (avoid in G6PD deficiency)
  • Amoxicillin/clavulanate 500/125 mg BID for 5-7 days
  • Cefuroxime 250 mg BID for 5 days
  • Cephalexin 500 mg BID for 5 days
  • Fosfomycin 3 g single dose (useful for resistant bacteria, avoid if GFR <30 mL/min)
  • Avoid trimethoprim in first trimester and near term; avoid sulfa after 32 weeks (risk of kernicterus).
  • Contraindicated: fluoroquinolones, tetracyclines.

Treatment Prior to Urologic Procedures

  • Antibiotics started night before or immediately prior to procedure.
  • Continue until catheter removal.

Follow-Up & Monitoring

  • Post-treatment urine culture in pregnancy recommended by ACOG.
  • Monitor for development of symptomatic UTI.
  • Cranberry products may reduce ASB frequency in pregnancy but evidence limited.

Complications

  • Untreated ASB in pregnancy leads to 20-35% pyelonephritis rate.
  • Pyelonephritis associated with premature delivery, low birth weight, neonatal GBS infection.
  • Untreated ASB before urologic procedures increases risk of bacteremia (up to 60%) and sepsis (5-10%).

Patient Education

  • ASB generally benign, treatment only in pregnancy or before specific procedures.
  • Pyuria and positive nitrites alone do not require antibiotics.
  • Seek care if symptoms of UTI develop.

Clinical Pearls

  • ASB treatment not recommended outside pregnancy or pre-urologic procedure setting.
  • Overtreatment increases antimicrobial resistance and side effects.
  • Screening and treatment of ASB in other populations do not reduce morbidity.