• Clinical science

Urinary tract infections

Abstract

Urinary tract infections (UTIs) are classified based on location as upper or lower UTIs, and based on presentation as complicated or uncomplicated. In particular, infection of the bladder is known as cystitis. UTIs are most commonly caused by Enterobacteriaceae, especially Escherichia coli. Women are at high risk of contracting UTIs due to a shorter urethra and the proximity of the anal and genital regions. Other risk factors include sexual intercourse, indwelling urinary catheters, pregnancy, and abnormalities of the urinary tract. Patients present with suprapubic pain, dysuria, urinary urgency and frequency. In typical presentations, clinical diagnosis is often possible and can be supported with findings of pyuria on urinalysis or positive leukocyte esterase and nitrites on a urine dipstick test. Further evaluation with urine culture and/or imaging may be required for patients with complicated cystitis. First-line empiric treatment options for uncomplicated cystitis include trimethoprim-sulfamethoxazole, nitrofurantoin, and fosfomycin. Pregnant women with cystitis should be screened and treated for asymptomatic bacteriuria.

Etiology

Pathogens

Predisposing factors

References:[1][2][3]][4]

Classification

Location

Type

Criteria
Uncomplicated UTI

Immunocompetent, premenopausal women that are neither pregnant nor have any condition that predisposes them to an increased risk of infection or failed therapy (see list below)

Complicated UTI

Any condition or comorbidity that may predispose a patient to an increased risk of infection or failed therapy such as:

Recurrent UTI

≥ 2 infections/6 months

or

≥ 3 infections/year

Nosocomial urinary tract infection

References:[1][5][6][7][8]

Clinical features

  • Dysuria, frequency, urgency
  • Suprapubic pain
  • Gross hematuria may be present

Fever is usually absent in lower UTIs; therefore, fever and flank pain should be taken as a sign of more serious infection, such as pyelonephritis.

References:[1][2]

Diagnostics

Clinical

  • Clinical diagnosis in healthy women with a typical presentation
  • In patients with an atypical presentation, urinalysis is the most important diagnostic test for cystitis.

Laboratory tests

Dipstick urine test

  • Best initial test
  • Findings indicative of UTI
    • Positive leukocyte esterase
    • Positive nitrites
    • Urine pH may be > 7 (alkaline) in Proteus mirabilis infections

Urinalysis with microscopy

  • Confirmatory test
  • Required in children and adolescents
  • Clean-catch midstream specimen is necessary to avoid contamination with vaginal or skin flora. Straight catheterization of the bladder or suprapubic aspiration can also be performed if a clean catch cannot be obtained without contamination (e.g., in children who are not toilet trained.)
  • Diagnostic criteria for UTI
    • Pyuria: ≥5-10 WBC/high power field (hpf)
    • Bacteriuria: presence of bacteria on Gram stain (most commonly, gram-negative rods)
  • Other possible findings include hematuria and mild proteinuria.
  • Leukocyte casts should be absent in lower UTIs.

Urine culture

Diagnostic imaging

References:[1][2][9][10][11][12][13][14][15]

Differential diagnoses

Interstitial cystitis (painful bladder syndrome)

  • Description: rare, chronic, noninfectious cystitis with an unknown etiology; that causes suprapubic pain and scarring of the bladder wall
  • Clinical findings
    • Suprapubic pain or discomfort
      • Relieved by voiding and worsened by bladder filling (most common feature)
      • Other exacerbating factors include sexual activity, exercise, alcohol use, and prolonged sitting
    • Urgency and frequency
    • Symptoms for at least 6 weeks
  • Diagnosis
  • Therapy
    • Behavior modification (first-line): avoid triggers, fluid management based on symptoms, bladder training
    • Oral medications (second-line): Amitriptyline is most commonly used and works as an analgesic and antidepressant.
    • Invasive procedures in the bladder (third-line)
      • Intravesical administration of lidocaine with either heparin or sodium bicarbonate can also be used for severe breakthrough pain
      • Bladder hydrodistention, which can also be diagnostic.
      • Removal or steroid injection of Hunner lesions

Other differential diagnoses

References:[16][17][18][19]

The differential diagnoses listed here are not exhaustive.

Treatment

Antibiotic therapy of uncomplicated UTIs

Principles of therapy

First-line treatment for acute uncomplicated cystitis in nonpregnant women

Second-line treatment

Antibiotic therapy of complicated UTIs

Therapy in pregnant women

Treatment of recurrent infections

  • If the patient becomes symptomatic within 2 weeks after treatment for a prior UTI has ceased, the patient can be restarted on the same treatment for 2 additional weeks and a urine culture should be obtained.
  • A single recurrent infection can be treated as an uncomplicated UTI.
  • Chemoprophylaxis can be given to patients with > 2 UTIs per year.
    • Postcoital prophylaxis or at the onset of initial symptoms with a single dose of TMP-SMX
    • Continuous prophylaxis with low-dose TMP-SMX for 6 months.

References:[1][13][20][19]

Complications

We list the most important complications. The selection is not exhaustive.

Prevention

  • Increased fluid intake
  • Postcoital voiding
  • Removal of urinary catheter if the patient is ambulatory and able to use the toilet independently
  • Intermittent straight catheterization is preferred in patients with neurogenic bladder.
  • Intermittent catheterization, instead of the placement of an indwelling catheter, also reduces catheter-associated UTIs
  • Prophylaxis in recurrent urinary tract infections (see “Treatment of recurrent infections” above)

References:[21]

Special patient groups

Pregnancy

Children and adolescents

  • Diagnosis
    • Urinalysis and urine culture
      • Criteria for diagnosis includes both a positive urinalysis; (pyuria; and/or bacteriuria; ) and urine culture (> 50,000 CFU/mL).
      • A clean-catch urine sample may be obtained if the child is toilet trained. If not trained, a straight catheterization is necessary.
      • Indicated in patients with suspected UTI that fulfill one of the following criteria:
        • Females and uncircumcised males of < 24 months of age with one of the following risk factors: either fever of unknown source or of duration > 24 hours, history of UTI, ill appearance, suprapubic tenderness, or nonblack race
        • Circumcised boys < 24 months of age with at least two of the above risk factors
        • Children older than 24 months with a suspected UTI based on urinary symptoms (see “Clinical features” section)
        • Any febrile infant or child with an abnormal urinary tract or family history of urinary tract disease
    • Renal and bladder ultrasound
      • Indications:
        • Infants aged 2–24 months with a febrile UTI
        • Children with either treatment failure, abnormal voiding, abdominal mass, recurrent UTI, or poor likelihood of follow-up
    • Voiding cystourethrography (VCUG)
  • Treatment

References:[11][22][23][24]