Asymptomatic Bacteriuria (ASB)

• General Prevalence:
  • Common among elderly patients in community, residential aged care facilities, and hospitals.
  • Increases with age.
• Men:
  • 0% in men aged 68-79 years.
  • 5.4% in men aged 90-103 years.
• Women:
  • 13.6% in women aged 68-79 years.
  • 22.4% in women aged 90-103 years.
• Institutionalized Patients:
  • Women: 25-50%.
  • Men: 15-35%.
• Hospitalized Elderly Patients:
  • Women: 32-50%.
  • Men: 30-34%.
• Stroke Patients:
  • 11.8% in subacute and chronic stroke patients.

Aetiology of ASB

• Common Pathogens:
  • Escherichia coli: Most common.
  • Klebsiella pneumoniae.
  • Proteus mirabilis.
  • Enterococcus faecalis.
  • Coagulase-negative Staphylococcus.
  • Group B Streptococcus.
• Institutionalized Patients:
  • Proteus mirabilis most frequently isolated.
• Long-term Urinary Catheters:
  • Polymicrobial bacteriuria common.
  • Includes Pseudomonas aeruginosa, Morganella morganii, Providencia stuartii.

Risk Factors for ASB

• Structural Abnormalities:
  • Renal calculi: Cause irritation, inflammation, urinary stasis, and obstruction.
• Comorbid Conditions:
  • Alzheimer’s dementia.
  • Parkinson’s disease.
  • Cerebrovascular disease: Affect bladder motility and continence.
  • Diabetes mellitus: Neurogenic bladder, diabetic microangiopathy, hyperglycemia-induced immune impairment.
  • Primary biliary cirrhosis: Increased ASB risk.
• High Postvoid Residual (PVR) Volume:
  • PVR >180 mL in asymptomatic men: 87% predictive value for positive urine culture.
  • Higher mean PVR associated with UTI in asymptomatic male patients.
• Indwelling Catheter:
  • Short-term catheterization: 9-23% ASB prevalence.
  • Long-term catheterization (>30 days): 100% ASB prevalence.
• Community Dwelling Elderly:
  • Urinary incontinence: OR 2.99.
  • Reduced mobility: OR 2.68.
  • Estrogen treatment: OR 2.20.
• Chronic Constipation:
  • Risk factor for lower urinary tract symptoms and ASB.
  • Potential to cause progressive neuropathy in the pelvic floor and urinary retention.
  • Associated with urinary incontinence (OR 1.46).
  • Can lead to overflow fecal incontinence and perineal soiling, increasing infection risk.

Diagnosis of Asymptomatic Bacteriuria (ASB) in Elderly Patients

• Challenges:
  • Difficult to diagnose ASB and decide against antibiotics in clinical practice, especially in elderly.
  • Elderly patients may have language barriers or cognitive impairments, making history-taking unreliable.
  • Nonspecific systemic symptoms (lethargy, weakness, loss of appetite) complicate diagnosis.
• Long-term Care Facilities:
  • Multiple triggers for urine cultures, including nonspecific symptoms (irritability, aggressiveness).
  • Reliance on nursing staff judgment for ordering urine cultures, but information may be incomplete or unreliable.
• Urine Sample Collection:
  • Difficult for elderly patients to produce clean-catch samples, leading to contaminated and hard-to-interpret results.
  • Fever and leukocytosis are less common in elderly, making infection detection challenging.
• Urine Dipstick:
  • Not reliable for diagnosing ASB or cystitis.
  • Useful as a ‘rule out’ test if nitrate and leukocyte esterase are both negative.
  • Positive leukocyte esterase correlates with bacteriuria in only 50% of patients.
  • Pyuria is not a sensitive or specific predictor of bacteriuria in the elderly.
• Urinary Cytokines:
  • Testing for urinary cytokines (e.g., IL-6) has shown promise but requires larger trials for validation.
  • IL-6: 81% sensitivity, 96% specificity.
  • Leukocyte esterase: 88% sensitivity, 79% specificity.

Complications of ASB in Elderly Patients

• Mortality:
  • Early studies suggested reduced survival, but recent studies show no significant difference in mortality.
  • ASB in men previously associated with increased cancer frequency, but not increased mortality.
• Morbidity:
  • No proven increase in morbidity from ASB.
  • Studies show no association between ASB and reduced creatinine clearance or new onset hypertension in diabetic women.
• Infection Risk:
  • Some association with acute cystitis in postmenopausal women and urosepsis in diabetic patients.
  • No proven benefit from antimicrobial treatment in reducing mortality or genitourinary morbidity.

Management of ASB

• Guidelines:
  • Infectious Disease Society of America (IDSA) and Australian guidelines recommend against routine screening and treatment of ASB in elderly, community dwellers, or institutionalized patients.
  • Antibiotics not recommended for patients with indwelling catheters, diabetic women, or those with spinal cord injury.
• Risks of Unnecessary Treatment:
  • Adverse effects of antibiotics.
  • Development of resistant organisms.
  • Increased risk of drug interactions and Clostridium difficile diarrhea.
• When to Treat:
  • Patients with abnormal urinary tracts or persistent bacteriuria 48 hours after clean intermittent catheterization, genitourinary manipulation, or instrumentation with high mucosal bleeding risk.
  • Symptomatic bacteriuria (bacteremia with same organism, acute pyelonephritis, acute lower tract symptoms, catheter trauma/obstruction).
• Prevention Measures:
  • Avoid long-term indwelling catheters.
  • Use sterile technique for catheter insertion.
  • Good catheter care, early detection of blockage, and prevention of constipation with oral laxatives.
  • Systemic antimicrobial agents not routinely used post-catheterization due to cost, side effects, and resistance.
  • Intravaginal estriol and cranberry juice may help prevent ASB.