12. Urinary Tract Infections

Definitions

  • Contamination: organisms are introduced during collection or processing of urine. No health care concerns.
  • Asymptomatic bacteriuria: colonization without illness or symptoms. IDSA defines as >100K CFU/mL of the same organism on two consecutive clean catch samples in women and one sample in men. The presence of pyuria (WBC) on urinalysis does not differentiate symptomatic from asymptomatic bacteriuria. Often does not require treatment except in special circumstances (see below).
  • Lower UTI: urethritis, cystitis.
  • Upper UTI: pyelonephritis, renal/perinephric abscess.
  • Uncomplicated UTI: lower UTI in a healthy, non-pregnant woman with normal GU anatomy and function.
  • Complicated UTI: anyone else including upper UTI in women, any UTI in men, pregnant women or women with structural or neurological GU disease.
    • Consider if patient has known outlet obstruction, stone disease, diverticulum, neurogenic bladder, VUR, has had recent instrumentation of urinary tract, has systemic disease (e.g. CKD, diabetes, immunodeficiency, organ transplantation), is pregnant, has known history of multi-drug resistant bacteria or if the current urinalysis suggests MDRO.
  • Recurrent UTI: occurring after documented infection that had resolved. Two or more infections in 6 months, or ≥3 infections in 12 months.
  • Reinfection UTI: a new event with reintroduction of bacteria into the urinary tract or by different bacteria.
  • Persistent UTI: UTI caused by same bacteria from focus of infection.
  • Catheter-associated UTI (CAUTI): patients with indwelling urinary catheter (IUC) will universally develop bacteriuria over time with 10-25% developing symptoms. Particularly common in women, elderly individuals, those with T2DM. Per IDSA, consider in those with IUC or within 48 hours of catheter removal with culture positive for 1000 CFU/mL and any of fever, suprapubic tenderness, CVA tenderness, mental status change, hypotension, SIRS.

Etiology and Risk Factors

  • Organisms: SEEEKS PP: Serratia, E. coli (80%), Enterobacter, Enterococcus, Klebsiella, S. saprophyticus (5-15% of outpatient UTIs), Proteus, Pseudomonas.
    • S. aureus, candida spp, and Mycobacterium tuberculosis can cause UTI via hematogenous spread.
    • Normal perineal flora: Lactobacillus, Corynebacterium, Staphylococcus, Streptococcus.
  • Risk factors: 
    • Ascending infection:
      • Reduced urine flow: outflow obstruction (BPH, prostate cancer, urethral stricture, pelvic organ prolapse, foreign body), neurogenic bladder, poor fluid intake, voiding dysfunction.
      • Promote colonization: short urethra (females), sexual activity, spermicide (increase bacterial binding), estrogen depletion, antimicrobial agents (decrease native flora).
      • Facilitate ascent: catheterization, urinary incontinence, fecal incontinence, residual urine with ischemia of bladder wall.
    • Hematogenous spread:
      • Uncommon except in those with immunocompromise, elderly, neonates.

Evaluation

History and physical exam:

  • Lower UTI: dysuria, frequency, urgency, suprapubic tenderness, hematuria, foul-smelling urine.
  • Upper UTI: costovertebral angle tenderness, fever, rigors, flank pain, nausea, vomiting.
  • If complicated by sepsis: hypotension, AMS.
  • Differential diagnosis: vulvovaginitis, pelvic inflammatory disease, prostatitis, epididymitis, orchitis, renal stone, chemotherapy (cyclophosphamide-induced hemorrhagic cystitis), interstitial cystitis, overactive bladder, vaginal atrophy, pelvic floor muscle dysfunction, candidal infection, urinary tuberculosis, intra-abdominal abscess, sepsis from non-GU source, STI (HSV, GC/CT, Trichomonas).
    • Recurrent/persistent UTI: lower urinary tract neoplasm, bladder outlet obstruction, diverticulum, fistula, vesicoureteral abnormality, infected stone, foreign body, voiding dysfunction, infected urachal cyst, chronic bacterial prostatitis.

Labs:

  • UA and culture: expect WBCs, bacteria, proteinuria, +/- hematuria. Leukocyte esterase indicates the presence of WBCs. Nitrites indicate the presence of gram-negative bacteria. WBC casts indicate renal involvement. High pH seen in Proteus infection.
    • Different UA collection methods: clean catch midstream voided urine (particularly in females, this method is susceptible to contamination), catheterized urine, suprapubic aspiration.
    • Presence of leukocyte esterase has 73-84% specificity and 80-92% sensitivity.
    • Presence of nitrites is 96-99% specific but only 41-57% sensitive.
    • Microscopy: >10WBC/hpf is 95% sensitive but not specific for UTI, more than 15-20/hpf of squamous epithelial cells is suggestive of contaminated specimen.
    • CFU by collection method: in general >100,000 CFU/mL of single species of bacteria from clean catch is suggestive of UTI; catheterized or aspirated specimens with lower CFU counts may also suggest UTI given they are more likely to be sterile and less likely to represent contamination.

Imaging:

  • Uncomplicated cystitis or uncomplicated pyelonephritis do not warrant imaging.
  • Imaging may be considered in those who do not respond to treatment, in patients with complicated UTIs, or recurrent UTIs.
  • Preferred imaging is with a kidney/bladder ultrasound or non-contrast CT abdomen and pelvis. Cystoscopy or ureteroscopy may be considered in cases of recurrent UTI to exclude bladder or upper tract pathology.

Management

  • Refer to your local antibiogram in addition to general recommendations below.
  • Asymptomatic bacteriuria: does not need treatment in the majority of patients. Treat in pregnant women, post renal transplant, in patients with neutropenia, and prior to urological surgery/instrumentation.
    • Otherwise, treatment has not been shown to decrease episodes of symptomatic infection and selects for antimicrobial resistance including in the elderly, patients with diabetes, or patients with indwelling catheters.
  • Uncomplicated UTI: TMP/SMX DS 1 pill BID for 3 days, fosfomycin 3g single PO dose for 1 day, nitrofurantoin (Macrobid) 100mg BID for 5 days, or cephalexin. Use fluoroquinolone (PO ciprofloxacin 250mg BID for 3 days) if local TMP/SMX resistance is >20%.
    • Recent studies show a one day regimen of 3rd or 4th generation fluoroquinolones may be sufficient.
  • Lower UTI in pregnant women: amoxicillin/clavulanate (Augmentin) and cephalexin are preferred.
  • Complicated UTI (including pyelonephritis):
    • If previous relevant microbiology is available, this can be used to guide antimicrobial choice. Also consider local resistance prevalence (e.g., TMP/SMX >20%, fluoroquinolones >10%) and patient risk factors for antibiotic resistance.
    • In patients who require hospitalization, empiric therapy can include: broad spectrum cephalosporin (e.g., ceftriaxone, cefepime) +/- aminoglycoside, combination beta-lactam and a beta-lactamase inhibitor (e.g., piperacillin-tazobactam), carbapenem, or fluoroquinolone.
    • Source control:
      • If patient has IUC, remove them, or if not possible to discontinue, replace catheter.
      • If urinary stent or renal stones are present, discuss removal with urology.
    • Switch from IV to PO after 48 hours of clinical improvement. Tailor antibiotics based on culture susceptibility data. Options include:
      • PO ciprofloxacin 500mg BID or PO cipro ER 1g for 5-7 days.
      • PO levofloxacin 750mg daily for 5-7 days.
      • PO TMP/SMX DS BID for 7-10 days (not for Enterococcus or Pseudomonas). 
      • Optimal duration of treatment is not well-established. Longer therapy is indicated if there is a nonremovable nidus of infection or delayed response to therapy. 
  • Bacterial prostatitis:
    • Organisms: E. coli, Enterobacter, Pseudomonas, Enterococcus.
    • Treat for 14 days.
    • 1st line: TMP/SMX or fluoroquinolone.
    • 2nd line: 2nd generation cephalosporin.
    • 3rd line: 3rd generation cephalosporin.
  • Antibiotic prophylaxis for persistent or recurrent UTI:
    • ID consult may be warranted.
    • Should be continued for at least 6 months.
    • Options: PO fosfomycin 3g q10days, Macrobid 50-100mg daily, cephalexin 125-250mg daily.
    • Post-coital prophylaxis: Macrobid 50-100mg single dose, TMP/SMX SS single dose, cefixime 400mg single dose.

 

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Kaplan, D, Yates, J, et al. Medical Student Curriculum: Adult UTI. 2020. American Urological Association Education and Research Inc. Accessed at https://www.auanet.org/education/auauniversity/for-medical-students/medical-students-curriculum/medical-student-curriculum/adult-uti

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